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DOI: 10.1055/a-2314-1877
Modular Synthesis of Conjugated Aromatic Boronate Esters by Radical Xanthate Addition
We thank the China Scholarship Council (scholarship to C.H.), the National Natural Science Foundation of China (22322103 and 22271057), the Natural Science Foundation of Shanghai Municipality (22ZR1406000), and the State Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science, Fudan University for support.
Abstract
Conjugated aromatic boronate esters serve as crucial intermediates in the synthesis of pharmaceuticals and polymer materials. Traditional methods for their synthesis typically involve organoboration of aromatic ring compounds, where pre-constructions of aromatic rings are required. Here, we present a general strategy for the synthesis of diverse conjugated aromatic boronate esters based on the radical addition of xanthates. Through this method, we synthesized various boronate ester xanthates that could be utilized as a platform to furnish conjugated aromatic building blocks, including thiophenes, pyrroles, tetralones, naphthols, and naphthylamines. This cost-effective strategy holds promise as a viable method for the industrial-scale production of (hetero)aromatic boronate esters.
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Conjugated aromatic compounds traverse diverse scientific disciplines, rendering them a highly coveted class of chemical substances. Their exceptional electronic and structural properties have catalyzed groundbreaking advancements in electronics,[1] materials science,[2] medicine,[3] and renewable energy technologies.[4] For instance, they are key elements in conductive polymers, which paved the way for electronic devices, as well as in photothermal therapy and OLEDs.[5] Consequently, the development of practical synthetic methods for these compounds continues to be a worthwhile endeavor.
Xanthates and related dithiocarbonyl derivatives have emerged as unique mediators of various radical processes.[6] In particular, they exhibit the remarkable ability to add to unactivated, electronically unbiased alkenes.[6b] [7] The resulting adducts can be further employed in constructing aromatic rings such as pyridines,[8] pyrroles,[9] thiophenes,[10] tetralones, naphthalenes, and even higher aromatic structures.[11] Previous work from our laboratory has allowed the rational design and synthesis of various boronate-substituted xanthates, effectively enabling the construction of terminal or internal boronates[12] and boronate-containing pyrroles and furans.[13]
In pursuit of further research, we have successfully synthesized a series of xanthates bearing phenylboronate groups suitable for addition reactions. The adducts obtained proved to be general templates for synthesizing an array of boronate-containing conjugated aromatic compounds. Through these experiments, we have effectively demonstrated the feasibility of this innovative pathway and established the conditions that allow the desired transformations to take place without harm to the relatively fragile boronate substituent. These promising findings hold significant potential for advancing the field and opening up new possibilities in the realm of aromatic organoborons.
Considering the free-radical activity and the diversity of reactions, we chose acetophenone as the backbone of the xanthate partner, and equipped it with three different boronic acid/boronate esters, including a naked boronic acid, a highly coupling efficient N-methyliminodiacetic acid (MIDA) boronate ester,[14] and a widely used pinacol boronate ester. 4-(2-((Ethoxycarbonothioyl)thio)acetyl)phenylboronic acid (Xan-boronic, 1) was obtained from commercially available and inexpensive 4-acetylphenylboronic acid (4), which was brominated with N-bromosuccinimide in wet acetonitrile to give bromo ketone 5 [15] and the bromine displaced by potassium O-ethyl xanthate in excellent overall yield (Scheme [1]). 4-(2-((Ethoxycarbonothioyl)thio)acetyl)phenylboronate MIDA ester (Xan-BMIDA, 3) and 4-(2-((ethoxycarbonothioyl)thio)acetyl)phenylboronate pinacol ester (Xan-Bpin, 2) were prepared from Xan-boronic (1) through one-step condensation reactions in high yields. The two xanthates exhibit good air stability but have quite different polarities.
The additions of the three boronic acid/boronate ester xanthates to alkenes were conducted in refluxing ethyl acetate (EA) or dichloroethane (DCE) for 3–4 hours with dilauroyl peroxide (DLP) as the initiator, and silica gel chromatography was performed for purification (Scheme [2]). Whereas the addition of Xan-Bpin (2) and Xan-BMIDA (3) to various olefins showed wide applicability, Xan-boronic (1) remained, surprisingly, mostly intact. In general, the yields of the desired adducts from Xan-Bpin (2) were a little lower than those from Xan-BMIDA (Scheme [2]). We assume that it is because Bpin derivatives are easily adsorbed on silica gel, even with acidified silica gel, causing partial loss of product. Five equivalents of alkenes were added to obtain compounds 6 and 7 in comparable yield (>80%, except for 7b). Reducing the alkene amounts to 2–3 equivalents caused the yield of compounds 8 to 14 to drop to about 60%. In the case of product 13, the modest yield appears to be due to some double addition to the 1,7-octadiene partner.
After confirming the efficient addition to alkenes, we utilized adducts 12a/12b and their tetralone cyclized products 23a/23b to prepare a series of boronate-substituted (hetero)aromatic derivatives. The terminal carbon in adducts 12a/12b bearing the xanthate and pivaloyloxy groups has the oxidation level of an aldehyde, therefore making these compounds the synthetic equivalents of 1,4-keto aldehydes. In this respect, they could be converted in principle into pyrroles by a variation of the venerable Paal–Knorr reaction (Scheme [3]). We were pleased to find that the conditions required to liberate the latent aldehyde and induce condensation with the requisite amine did not affect the fragile boronate substituent, at least in the case of pinacolate esters. Thus, adducts 12a/12b were heated with a variety of amines in the presence of p-toluenesulfonic acid as a catalyst and using 1,4-dioxane as a solvent. From pinacolatoboronate adduct 12b, the corresponding pyrroles 15b–21b were successfully obtained in good yields (67–89%). In the case of pyrroles 19b and 20b derived from anilines, harsher conditions were required because of the lower nucleophilicity of anilines compared to primary aliphatic amines. A large excess of the respective aniline (12 equiv) had to be used and the reaction time was extended to 5 days. Unfortunately, the yields of (MIDA)boronate-substituted pyrroles 15a–21a from 12a were lower than those from 12b, presumably because of partial aminolysis of the (MIDA)boronate ester. Furthermore, no pyrroles 19a and 20a were obtained because the (MIDA)boronate ester did not survive the presence of a large excess of the anilines and the long heating period. Access to pyrroles 19a and 20a should nevertheless be possible by the well-known exchange of the pinacolatoboronate ester with an (MIDA)boronate by treatment with N-methyliminodiacetic acid. N-Unsubstituted pyrrole 18a could not be obtained pure due to its tendency to be oxidized in air.
We were also gratified to find that, at least in the case of pinacolatoboronate adduct 12b, the boron substituent survived the conditions needed for conversion into thiophene 22, which was obtained in quite a good yield (Scheme [4]A). Thus, heating compound 12b with potassium iodide and acetic acid in a microwave oven furnished thiophene 22 in 72% yield. The corresponding (MIDA)boronate-substituted analogue 12a, in contrast, was mostly decomposed under the same conditions, even if signals corresponding to thiophene could be observed in the 1H NMR spectrum of the crude product mixture.
In line with our previous work,[16] which established simple access to α-tetralones through further cyclization of adducts derived from phenacyl xanthates, we found that treatment of addition products 12a/12b with stoichiometric amounts of peroxide indeed furnished the corresponding tetralones (Scheme [4]B). Exposure of (MIDA)boronate-substituted adduct 12a to a stoichiometric amount of DLP in refluxing ethyl acetate (EA) induced clean cyclization into tetralone 23a in 77% yield. For adduct 12b, di-tert-butyl peroxide (DTBP) was used in place of DLP to avoid contamination by DLP-derived products, especially lauric acid. Because DTBP decomposes very slowly at 80 °C, the higher boiling chlorobenzene was chosen as the solvent instead of EA. Under these conditions, the desired tetralone 23b was produced in 50% yield alongside 38% of prematurely reduced side product 24, as calculated by 1H NMR. Because of unexpected difficulties in separating the two products, the subsequent transformations were performed on the mixture.
The acid-catalyzed aromatization was next examined on both tetralones 23a/23b (Scheme [5]). In the case of tetralone 23b, heating with p-toluenesulfonic acid, as in the original report,[16b] resulted in the decomposition of the boronate ester, whereas the use of the weaker acetic acid did not induce any reaction. After some experimentation, we found that treatment with AlCl3 and Et3N in toluene at 110 °C, in the presence of Na2SO4 to remove adventitious water, furnished the corresponding naphthol 25 in moderate yield (51%) (Scheme [5]A). Triethylamine is essential; without it, a black insoluble precipitate formed soon after the addition of the reagents. Unfortunately, none of these conditions were successful with tetralone 23a, and only decomposition was observed. Interestingly, prior formation of the Schiff bases by heating with various primary amines followed by the addition of AlCl3 produced the corresponding naphthylamines 26–29 (Scheme [5]B). The reaction yield is generally moderate, due in part to the strong adsorption of the products on silica gel.
Finally, we found that it was possible to brominate tetralone 23a in moderate yield by treatment with N-bromosuccinimide in acetic acid to afford bromotetralone 30 (Scheme [6]). The presence of bromine next to the ketone opens various avenues for further transformations using both ionic and radical methods. One possibility is its replacement with a xanthate, which would then allow intermolecular additions to various alkenes bearing a variety of functional groups.
In summary, we have defined conditions allowing the synthesis of boronate-substituted aromatic ketones by the metal-free radical addition of xanthates. These adducts could be converted into thiophene, various pyrrole, tetralone, naphthol, and naphthylamine derivatives. In general, the pinacolatoboronate was the better substituent as it was capable of surviving most of the experimental conditions. The starting material 4 and the reagents are commercially available and inexpensive. The presence of the boronate group opens up numerous opportunities for further diversification through the powerful Suzuki–Miyaura coupling, thus providing access to a plethora of compounds relevant to materials science and medicinal chemistry.
Commercial reagents and solvents were purchased from Sigma-Aldrich, Alfa Aesar, and Bidepharm, and were used without further purification. 1H NMR spectra were recorded at 400 MHz and coupling constants (J) are reported to ± 0.5 Hz. 13C NMR spectra were recorded at 100 MHz. High-resolution mass spectra were recorded by electron impact ionization (EI) on a JMS-GCMate II mass spectrometer or by electrospray ionization in positive mode (ESI+) on a timsTOF mass spectrometer (Bruker, France). Infra-red spectra were recorded on a Perkin-Elmer Spectrum Two FT-IR spectrometer. Melting points were recorded in degrees Celsius (°C), using a Stuart SMP40 automatic melting point apparatus.
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4-(2-((Ethoxycarbonothioyl)thio)acetyl)phenylboronic Acid (Xan-boronic, 1)
4-Acetylphenylboronic acid (4; 8.2 g, 50 mmol) and p-toluenesulfonic acid monohydrate (15.2 g, 80 mmol) were dissolved in mixed solvent (MeCN/H2O, 98:2; 150 mL). The solution was cooled to 0 °C, and then N-bromosuccinimide (10.7 g, 60 mmol) was added slowly. After being stirred overnight at room temperature, the solution was evaporated to remove the MeCN. The obtained white solid was extracted with ethyl acetate (EA)/H2O and the organics were evaporated to give the crude product as a white powder.
The obtained crude product was dissolved in acetone (500 mL) and the solution was cooled to 0 °C. Potassium O-ethyl xanthate (8.0 g, 50 mmol) was added slowly and the suspension was stirred at room temperature for 3 h. The acetone was removed in vacuo and the residue was extracted with EA/H2O. The EA layer was dried with Na2SO4 (do not use MgSO4). The target product was obtained as a white solid; yield: 12.6 g (89%); mp 136–137 °C.
IR (neat): 3382, 1681, 1401, 1346, 1308, 1288, 1222, 1145, 1111, 1047, 012, 989, 738, 709, 686, 630 cm–1.
1H NMR (400 MHz, DMSO-d 6): δ = 8.35 (s, 2 H), 7.97 (dd, J = 20.7, 8.3 Hz, 4 H), 4.86 (s, 2 H), 4.65–4.48 (m, 2 H), 1.25 (t, J = 7.1 Hz, 3 H).
13C NMR (101 MHz, DMSO-d 6): δ = 213.13, 192.57, 136.72, 134.29, 127.08, 70.59, 42.73, 13.39.
HRMS (EI+): m/z calcd for C11H14BO4S2 +: 285.0421; found: 285.0428.
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4-(2-((Ethoxycarbonothioyl)thio)acetyl)phenylboronate Pinacol Ester (Xan-Bpin, 2)
Xan-boronic (1; 5.7 g, 20 mmol) was dissolved in DCM (100 mL) and pinacol (3.5 g, 30 mmol) was added slowly. After being stirred at r.t. overnight, the solution was extracted with DCM/H2O. The organic layer was washed with saturated NaCl solution (5 times) and dried with Na2SO4. The target product was obtained by recrystallization (EA/PE, 1:1) as light yellow crystals; yield: 7.0 g (95%); mp 116–118 °C.
IR (neat): 1698, 1396, 1358, 1333, 1246, 1139, 1113, 1088, 1046, 995, 986, 960, 854, 822, 768, 736, 650 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.99 (d, J = 8.4 Hz, 2 H), 7.92 (d, J = 8.4 Hz, 2 H), 4.66 (s, 2 H), 4.62 (q, J = 7.1 Hz, 2 H), 1.38 (t, J = 7.1 Hz, 3 H), 1.36 (s, 12 H).
13C NMR (101 MHz, CDCl3): δ = 213.17, 192.66, 137.70, 135.09, 127.40, 84.31, 70.72, 43.60, 24.89, 13.74.
HRMS (EI+): m/z calcd for C17H24BO4S2 +: 367.1204; found: 367.1213.
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4-(2-((Ethoxycarbonothioyl)thio)acetyl)phenylboronate MIDA Ester (Xan-BMIDA, 3)
Xan-boronic (1; 6.3 g, 22 mmol), N-methyliminodiacetic acid (3.7 g, 25 mmol), and mixed solvent (toluene/DMSO, 95:5; 200 mL) were added to a bottle equipped with a Dean–Stark apparatus. After being stirred for 4 h at reflux temperature, the system turned dark yellow (or brown) with some sticky yellow solid. The toluene was removed in vacuo and then H2O was added to the bottle to form an off-white precipitate. The precipitate was filtered and washed several times with H2O to obtain the product as an off-white powder; yield: 7.5 g (86%); mp 131–133 °C.
IR (neat): 1748, 1675, 1451, 1339, 1300, 1219, 1113, 996, 984, 959, 890, 865, 850, 807, 770 cm–1.
1H NMR (400 MHz, DMSO-d 6): δ = 8.02 (d, J = 8.4 Hz, 2 H), 7.63 (d, J = 8.4 Hz, 2 H), 4.87 (s, 2 H), 4.56 (q, J = 7.1 Hz, 2 H), 4.38 (d, J = 17.2 Hz, 2 H), 4.16 (d, J = 17.1 Hz, 2 H), 2.53 (s, 3 H), 1.26 (t, J = 7.1 Hz, 3 H).
13C NMR (101 MHz, DMSO-d 6): δ = 213.22, 192.46, 169.27, 136.01, 132.87, 127.32, 70.61, 61.95, 47.63, 42.69, 13.40.
HRMS (EI+): m/z calcd for C16H19BNO6S2 +: 396.0741; found: 396.0749.
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Adducts 6–14; General Procedure for the Addition Reactions to Alkenes
A 5-mL vial equipped with a stirring bar was charged with xanthate (1 equiv), olefin (2–3 equiv), and dilauroyl peroxide (DLP, 15–20 mol% to xanthate) in EA or DCE (1.5 mL). Then, the vial was deoxygenated by pumping in nitrogen for 5 min and sealed with a cap. The reaction solution was then put into a preheated plate at 85 °C and heated for 3–4 h. The reaction mixture was then cooled to r.t. and purified by flash chromatography directly. The silica gel used for purifying boronate pinacol ester derivatives was acidified according to the literature.[17]
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4-(4-((Ethoxycarbonothioyl)thio)decanoyl)phenylboronate MIDA Ester (6a)
Xan-BMIDA (198 mg, 0.5 mmol), 1-octene (280 mg, 2.5 mmol), and DLP (40 mg, 0.1 mmol) were dissolved in EA (1.5 mL), and the solution was stirred at 85 °C for 3 h. Crude product was purified by flash chromatography (PE/EA, 3:2).
Yield: 217 mg (85%); white solid; mp 92–94 °C.
IR (neat): 1772, 1750, 1679, 1454, 1337, 1282, 1255, 1111, 1035, 992, 889, 871, 854, 831, 811 cm–1.
1H NMR (400 MHz, DMSO-d 6): δ = 7.92 (d, J = 8.3 Hz, 2 H), 7.59 (d, J = 8.2 Hz, 2 H), 4.63–4.49 (m, 2 H), 4.37 (d, J = 17.2 Hz, 2 H), 4.15 (d, J = 17.2 Hz, 2 H), 3.76 (dd, J = 9.5, 3.7 Hz, 1 H), 3.26–3.06 (m, 2 H), 2.54 (s, 3 H), 2.11 (td, J = 14.1, 7.1 Hz, 1 H), 1.92 (dt, J = 14.4, 7.2 Hz, 1 H), 1.79–1.57 (m, 1 H), 1.45–1.35 (m, 2 H), 1.30 (t, J = 7.1 Hz, 3 H), 1.25 (s, 7 H), 0.85 (t, J = 6.7 Hz, 3 H).
13C NMR (101 MHz, DMSO-d 6): δ = 213.77, 199.23, 169.24, 136.80, 132.73, 126.89, 70.02, 61.92, 50.46, 47.61, 35.29, 33.57, 31.05, 28.36, 28.01, 26.24, 21.99, 13.87, 13.45.
HRMS (EI+): m/z calcd for C24H35BNO6S2 +: 508.1993; found: 508.2004.
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4-(4-((Ethoxycarbonothioyl)thio)decanoyl)phenylboronate Pinacol Ester (6b)
Xan-Bpin (183 mg, 0.5 mmol), 1-octene (280 mg, 2.5 mmol), and DLP (30 mg, 0.075 mmol) were dissolved in DCE (1.5 mL), and the solution was stirred at 85 °C for 3 h. Crude product was purified by acidified flash chromatography (PE/EA, 97:3). The product was mixed with a little DLP residue.
Yield: 196 mg (82%); light yellow oil.
IR (neat): 2925, 2854, 1686, 1507, 1454, 1398, 1357, 1327, 1272, 1211, 1142, 1110, 1088, 1047, 1018, 962, 857, 824, 654 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.95–7.86 (m, 4 H), 4.69–4.53 (m, 2 H), 3.83 (m, 1 H), 3.13 (m, 2 H), 2.26 (m, 1 H), 2.06–1.91 (m, 1 H), 1.78–1.64 (m, 2 H), 1.39 (dd, J = 14.4, 7.2 Hz, 4 H), 1.36 (s, 12 H), 1.25 (s, 7 H), 0.88 (t, J = 6.8 Hz, 3 H).
13C NMR (101 MHz, CDCl3): δ = 214.52, 199.68, 138.69, 134.94, 127.03, 84.21, 69.86, 51.08, 36.01, 34.74, 31.68, 29.71, 29.11, 28.58, 26.85, 24.88, 22.59, 14.13, 14.08, 13.76.
HRMS (EI+): m/z calcd for C25H40BO4S2 +: 479.2456; found: 479.2474.
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4-(4-((Ethoxycarbonothioyl)thio)-4-(trimethylsilyl)butanoyl)phenylboronate MIDA Ester (7a)
Xan-BMIDA (198 mg, 0.5 mmol), vinyltrimethylsilane (250 mg, 2.5 mmol), and DLP (40 mg, 0.1 mmol) were dissolved in DCE (1.5 mL), and the solution was stirred at 85 °C for 3 h. Crude product was purified by flash chromatography (PE/EA, 3:2).
Yield: 207 mg (84%); white solid; mp 120–122 °C.
IR (neat): 1760, 1680, 1453, 1286, 1248, 1216, 1111, 1039, 990, 888, 836, 788, 752, 708, 647, 498 cm–1.
1H NMR (400 MHz, DMSO-d 6): δ = 7.88 (d, J = 8.3 Hz, 2 H), 7.58 (d, J = 8.3 Hz, 2 H), 4.60–4.43 (m, 2 H), 4.37 (d, J = 17.2 Hz, 2 H), 4.15 (d, J = 17.1 Hz, 2 H), 3.32 (s, 1 H), 3.24–3.14 (m, 2 H), 2.50 (s, 3 H), 2.35–2.17 (m, 1 H), 1.85–1.69 (m, 1 H), 1.26 (t, J = 7.1 Hz, 3 H), 0.12 (s, 9 H).
13C NMR (101 MHz, DMSO-d 6): δ = 215.36, 199.25, 169.24, 136.90, 132.74, 126.78, 70.52, 61.92, 47.60, 36.31, 35.89, 24.59, 13.43, –2.68.
HRMS (EI+): m/z calcd for C21H31BNO6S2Si+: 496.1450; found: 496.1464.
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4-(4-((Ethoxycarbonothioyl)thio)-4-(trimethylsilyl)butanoyl)phenylboronate Pinacol Ester (7b)
Xan-Bpin (183 mg, 0.5 mmol), vinyltrimethylsilane (250 mg, 2.5 mmol), and DLP (30.0 mg, 0.075 mmol) were dissolved in DCE (1.5 mL), and the solution was stirred at 85 °C for 3 h. Crude product was purified by acidified flash chromatography (PE/EA, 97:3).
Yield: 158 mg (68%); colorless oil.
IR (neat): 1685, 1507, 1397, 1355, 1327, 1249, 1210, 1142, 1110, 1088, 1043, 962, 837, 855, 652 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.92–7.85 (m, 4 H), 4.72–4.44 (m, 2 H), 3.25 (dd, J = 11.1, 3.5 Hz, 1 H), 3.22–3.05 (m, 2 H), 2.35 (m, 1 H), 1.83 (m, 1 H), 1.36 (t, J = 7.1 Hz, 3 H), 1.35 (s, 12 H), 0.19–0.12 (m, 9 H).
13C NMR (101 MHz, CDCl3): δ = 136.60, 134.83, 133.86, 128.25, 118.65, 108.58, 108.00, 83.84, 55.29, 34.94, 25.91, 25.44, 24.91.
HRMS (EI+): m/z calcd for C22H36BO4S2Si+: 467.1912; found: 467.1929.
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4-(4-((Ethoxycarbonothioyl)thio)-6,6-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)hexanoyl)phenylboronate MIDA Ester (8)
Xan-BMIDA (198 mg, 0.5 mmol), olefin but-3-ene-1,1,-diyldiboronate pinacol ester (308 mg, 1 mmol), and DLP (60.0 mg, 0.15 mmol) were dissolved in DCE (1.5 mL), and the solution was stirred at 85 °C for 3 h. Crude product was purified by flash chromatography (PE/EA, 3:2). Some product was absorbed on the silica gel.
Yield: 174 mg (50%); white solid; mp 158–160 °C.
IR (neat): 1765, 1681, 1451, 1367, 1295, 1216, 1166, 1136, 1111, 1041, 993, 968, 889, 865, 848, 829, 671, 578, 498 cm–1.
1H NMR (400 MHz, DMSO-d 6): δ = 7.91 (d, J = 8.3 Hz, 2 H), 7.59 (d, J = 8.2 Hz, 2 H), 4.63–4.46 (m, 2 H), 4.37 (d, J = 17.2 Hz, 2 H), 4.14 (d, J = 17.1 Hz, 2 H), 3.76–3.63 (m, 1 H), 3.12 (dd, J = 14.8, 7.9 Hz, 2 H), 2.50 (s, 3 H), 2.05 (m, 1 H), 1.97–1.84 (m, 2 H), 1.75 (m, 1 H), 1.29 (t, J = 7.1 Hz, 3 H), 1.23 (s, 1 H), 1.15 (m, 24 H).
13C NMR (101 MHz, DMSO-d 6): δ = 213.62, 199.05, 169.25, 136.83, 132.72, 126.84, 82.78, 69.97, 61.92, 52.82, 47.61, 35.26, 29.57, 28.34, 24.59, 24.57, 24.36, 24.24, 13.45.
HRMS (EI+): m/z calcd for C32H49B3NO10S2 +: 704.3072; found: 704.3092.
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4-(4-((Ethoxycarbonothioyl)thio)-5-(phthalimido)pentanoyl)phenylboronate MIDA Ester (9a)
Xan-BMIDA (79 mg, 0.2 mmol), N-allylphthalimide (112 mg, 0.6 mmol), and DLP (16 mg, 0.04 mmol) were dissolved in DCE (1 mL), and the solution was stirred at 85 °C for 3 h. Crude product was purified by flash chromatography (PE/EA, 3:2).
Yield: 66 mg (57%); white solid; mp 105–107 °C.
IR (neat): 1764, 1710, 1680, 1393, 1334, 1285, 1218, 1190, 1112, 1038, 888, 828, 723, 713, 530 cm–1.
1H NMR (400 MHz, DMSO-d 6): δ = 7.92 (d, J = 8.4 Hz, 2 H), 7.91–7.84 (m, 4 H), 7.58 (d, J = 8.4 Hz, 2 H), 4.54–4.41 (m, 2 H), 4.37 (d, J = 17.2 Hz, 2 H), 4.14 (d, J = 17.1 Hz, 2 H), 3.94 (d, J = 7.2 Hz, 2 H), 3.33 (s, 1 H), 3.28–3.19 (m, 2 H), 2.50 (s, 3 H), 2.17 (m, 1 H), 2.02–1.87 (m, 1 H), 1.28 (t, J = 7.1 Hz, 3 H).
13C NMR (101 MHz, DMSO-d 6): δ = 212.23, 198.93, 169.25, 167.70, 136.77, 134.58, 132.73, 131.35, 126.88, 123.18, 70.39, 61.92, 48.82, 47.62, 40.70, 35.19, 25.35, 13.27.
HRMS (EI+): m/z calcd for C27H28BN2O8S2 +: 583.1375; found: 583.1392.
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4-(4-((Ethoxycarbonothioyl)thio)-5-(phthalimido)pentanoyl)phenylboronate Pinacol Ester (9b)
Xan-Bpin (146 mg, 0.4 mmol), N-allylphthalimide (224 mg, 1.2 mmol), and DLP (32 mg, 0.08 mmol) were dissolved in DCE (1.5 mL), and the solution was stirred at 85 °C for 3 h. Crude product was purified by acidified flash chromatography (PE/EA, 4:1).
Yield: 117 mg (53%); colorless oil.
IR (neat): 1773, 1712, 1686, 1605, 1507, 1391, 1356, 1327, 1217, 1142, 1110, 1088, 1045, 855, 722, 714, 653 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.94–7.83 (m, 6 H), 7.72 (dd, J = 5.5, 3.0 Hz, 2 H), 4.57 (q, J = 7.1 Hz, 2 H), 4.25 (m, 1 H), 4.11–3.94 (m, 2 H), 3.30–3.12 (m, 2 H), 2.37–2.22 (m, 1 H), 2.08–1.93 (m, 1 H), 1.39 (t, J = 7.1 Hz, 3 H), 1.35 (s, 12 H).
13C NMR (101 MHz, CDCl3): δ = 211.28, 197.94, 167.10, 137.49, 133.91, 133.11, 130.83, 125.99, 122.47, 83.19, 69.32, 47.90, 40.10, 34.64, 24.70, 23.85, 12.62.
HRMS (EI+): m/z calcd for C28H33BNO6S2 +: 554.1835; found: 554.1850.
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4-(4-((Ethoxycarbonothioyl)thio)-6-phenylhexanoyl)phenylboronate MIDA Ester (10a)
Xan-BMIDA (158 mg, 0.4 mmol), 4-phenyl-1-butene (264 mg, 2 mmol), and DLP (24 mg, 0.06 mmol) were dissolved in DCE (1.5 mL), and the solution was stirred at 85 °C for 3 h. Crude product was purified by flash chromatography (PE/EA, 2:3).
Yield: 122 mg (58%); white powder; mp 80–82 °C.
IR (neat): 1760, 1679, 1452, 1334, 1284, 1215, 1111, 1038, 987, 888, 869, 813, 748, 699, 646 cm–1.
1H NMR (400 MHz, DMSO-d 6): δ = 7.93 (d, J = 8.2 Hz, 2 H), 7.59 (d, J = 8.2 Hz, 2 H), 7.33–7.13 (m, 5 H), 4.63–4.48 (m, 2 H), 4.37 (d, J = 17.3 Hz, 2 H), 4.14 (d, J = 17.2 Hz, 2 H), 3.85–3.70 (m, 1 H), 3.26–3.07 (m, 2 H), 2.72 (m, 2 H), 2.50 (s, 3 H), 2.18 (m, 1 H), 2.01 (m, 3 H), 1.27 (t, J = 7.1 Hz, 3 H).
13C NMR (101 MHz, DMSO-d 6): δ = 213.42, 199.22, 169.25, 141.11, 136.81, 132.73, 128.31, 126.91, 125.89, 70.08, 61.93, 50.00, 47.62, 35.38, 35.23, 32.50, 27.95, 13.43.
HRMS (EI+): m/z calcd for C26H31BNO6S2 +: 528.1680; found: 528.1694.
#
4-(4-((Ethoxycarbonothioyl)thio)-6-phenylhexanoyl)phenylboronate Pinacol Ester (10b)
Xan-Bpin (183 mg, 0.5 mmol), 4-phenyl-1-butene (265 mg, 2 mmol), and DLP (30 mg, 0.075 mmol) were dissolved in DCE (2 mL), and the solution was stirred at 85 °C for 3 h. Crude product was purified by acidified flash chromatography (PE/Et2O, 10:1).
Yield: 112 mg (46%); colorless oil.
IR (neat): 1684, 1506, 1452, 1397, 1356, 1326, 1272, 1210, 1142, 1110, 1088, 1046, 1018, 961, 856, 734, 699, 652 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.90 (q, J = 8.4 Hz, 4 H), 7.33–7.24 (m, 3 H), 7.19 (m, 2 H), 4.72–4.45 (m, 2 H), 3.95–3.78 (m, 1 H), 3.24–3.05 (m, 2 H), 2.90–2.69 (m, 2 H), 2.38–2.24 (m, 1 H), 2.13–1.94 (m, 3 H), 1.36 (t, J = 7.1 Hz, 3 H), 1.36 (s, 12 H).
13C NMR (101 MHz, CDCl3): δ = 214.00, 199.53, 141.31, 138.66, 134.97, 128.47, 128.42, 127.04, 126.06, 84.23, 69.98, 50.55, 36.71, 35.95, 33.23, 28.64, 24.90, 13.75.
HRMS (EI+): m/z calcd for C27H36BO4S2 +: 499.2143; found: 499.2153.
#
4-(4-((Ethoxycarbonothioyl)thio)-7-oxooctanoyl)phenylboronate MIDA Ester (11a)
Xan-BMIDA (80 mg, 0.2 mmol), 2-hexen-2-one (98 mg, 1 mmol), and DLP (16 mg, 0.04 mmol) were dissolved in DCE (1.0 mL), and the solution was stirred at 85 °C for 3 h. Crude product was purified by flash chromatography (PE/EA, 3:7).
Yield: 59 mg (60%); off-white solid; mp 80–82 °C.
IR (neat): 1760, 1710, 1679, 1451, 1363, 1335, 1283, 1215, 1111, 1037, 985, 888, 869, 813, 708, 646 cm–1.
1H NMR (400 MHz, DMSO-d 6): δ = 7.93 (d, J = 8.2 Hz, 2 H), 7.59 (d, J = 8.2 Hz, 2 H), 4.57 (m, 2 H), 4.37 (d, J = 17.2 Hz, 2 H), 4.14 (d, J = 17.2 Hz, 2 H), 3.84–3.67 (m, 1 H), 3.15 (dd, J = 15.3, 8.2 Hz, 2 H), 2.59 (dd, J = 8.9, 5.9 Hz, 2 H), 2.51 (s, 3 H), 2.09 (s, 3 H), 2.09 (t, J = 10.3 Hz, 1 H), 2.03–1.89 (m, 2 H), 1.83 (m, 1 H), 1.31 (t, J = 7.1 Hz, 3 H).
13C NMR (101 MHz, DMSO-d 6): δ = 213.49, 207.47, 199.17, 169.25, 136.81, 132.73, 126.89, 70.17, 61.92, 50.05, 47.62, 35.25, 29.77, 27.87, 27.41, 13.44.
HRMS (EI+): m/z calcd for C22H29BNO7S2 +: 494.1473; found: 494.1485.
#
4-(4-((Ethoxycarbonothioyl)thio)-7-oxooctanoyl)phenylboronate Pinacol Ester (11b)
Xan-Bpin (183 mg, 0.5 mmol), 2-hexen-2-one (197 mg, 2.0 mmol), and DLP (30 mg, 0.075 mmol) were dissolved in DCE (2 mL), and the solution was stirred at 85 °C for 3 h. Crude product was purified by acidified flash chromatography (PE/Et2O, 10:1).
Yield: 96 mg (42%); colorless oil.
IR (neat): 1715, 1683, 1507, 1398, 1355, 1327, 1211, 1142, 1110, 1088, 1044, 1018, 984, 962, 856, 734, 652 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.89 (q, J = 8.4 Hz, 4 H), 4.67–4.51 (m, 2 H), 3.81 (dt, J = 13.9, 4.5 Hz, 1 H), 3.15 (m, 2 H), 2.64 (t, J = 7.4 Hz, 2 H), 2.27–2.16 (m, 1 H), 2.15 (s, 3 H), 2.14–2.04 (m, 1 H), 2.04–1.84 (m, 2 H), 1.38 (t, J = 7.1 Hz, 3 H), 1.35 (s, 12 H).
13C NMR (101 MHz, CDCl3): δ = 212.98, 206.68, 198.40, 137.60, 133.93, 125.99, 83.20, 69.12, 49.60, 39.71, 34.88, 29.07, 27.79, 27.40, 23.86, 12.72.
HRMS (EI+): m/z calcd for C23H34BO5S2 +: 465.1935; found: 465.1941.
#
4-(4-((Ethoxycarbonothioyl)thio)-4-(pivaloyloxy)butanoyl)phenylboronate MIDA Ester (12a)
Xan-BMIDA (790 mg, 2.0 mmol), vinyl pivalate (1.3 g, 10.0 mmol), and DLP (80 mg, 0.2 mmol) were dissolved in EA (8 mL), and the solution was stirred at 85 °C for 3 h. Crude product was purified by flash chromatography (PE/EA, 2:3).
Yield: 744 mg (71%); off-white solid; mp 82–84 °C.
IR (neat): 1764, 1682, 1457, 1396, 1335, 1276, 1219, 1133, 1111, 1037, 986, 888, 869, 815, 766, 708, 498 cm–1.
1H NMR (400 MHz, DMSO-d 6): δ = 7.92 (d, J = 8.2 Hz, 2 H), 7.60 (d, J = 8.2 Hz, 2 H), 6.59 (t, J = 6.7 Hz, 1 H), 4.60 (dt, J = 6.9, 5.2 Hz, 2 H), 4.37 (d, J = 17.1 Hz, 2 H), 4.15 (d, J = 17.2 Hz, 2 H), 3.17 (t, J = 6.9 Hz, 2 H), 2.51 (s, 3 H), 2.29 (dt, J = 14.0, 6.8 Hz, 2 H), 1.33 (t, J = 7.1 Hz, 3 H), 1.12 (s, 9 H).
13C NMR (101 MHz, DMSO-d 6): δ = 209.84, 198.22, 175.84, 169.24, 136.56, 132.78, 126.91, 79.44, 70.65, 61.94, 47.62, 38.31, 33.65, 27.79, 26.78, 26.53, 13.39.
HRMS (EI+): m/z calcd for C23H30BNNaO8S2 +: 546.1398; found: 546.1408.
#
4-(4-((Ethoxycarbonothioyl)thio)-4-(pivaloyloxy)butanoyl)phenylboronate Pinacol Ester (12b)
Xan-Bpin (3.7 g, 10 mmol), vinyl pivalate (5.1 g, 40 mmol), and DLP (600.0 mg, 1.5 mmol) were dissolved in DCE (20.0 mL), and the solution was stirred at 85 °C for 3 h. Crude product was purified by acidified flash chromatography (PE/EA, 97:3). The product was mixed with a little DLP residue.
Yield: 3.4 g (69%); colorless oil.
IR (neat): 1736, 1687, 1507, 1397, 1357, 1328, 1272, 1221, 1139, 1110, 1088, 1047, 1031, 1001, 961, 856, 821, 652 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.93–7.87 (m, 4 H), 6.71 (t, J = 6.5 Hz, 1 H), 4.67–4.58 (m, 2 H), 3.13 (m, 2 H), 2.47–2.28 (m, 2 H), 1.41 (t, J = 7.1 Hz, 3 H), 1.35 (s, 12 H), 1.19 (s, 9 H).
13C NMR (101 MHz, CDCl3): δ = 210.10, 198.23, 176.78, 138.35, 135.00, 127.00, 84.26, 80.20, 70.27, 38.89, 34.37, 28.54, 26.98, 24.88, 13.69.
HRMS (EI+): m/z calcd for C24H35BNaO6S2 +: 517.1860; found: 517.1852.
#
4-(4-((Ethoxycarbonothioyl)thio)dec-9-enoyl)phenylboronate MIDA Ester (13)
Xan-BMIDA (79 mg, 0.2 mmol), 1,7-octadiene (220 mg, 2 mmol), and DLP (8.0 mg, 0.02 mmol) were dissolved in EA (1.5 mL), and the solution was stirred at 85 °C for 3 h. Crude product was purified by flash chromatography (PE/EA, 1:1).
Yield: 38 mg (38%); white solid; mp 71–73 °C.
IR (neat): 1758, 1679, 1453, 1336, 1283, 1215, 1111, 1038, 987, 908, 889, 870, 814, 708, 646, 456 cm–1.
1H NMR (400 MHz, DMSO-d 6): δ = 7.92 (d, J = 8.2 Hz, 2 H), 7.59 (d, J = 8.2 Hz, 2 H), 5.79 (ddt, J = 16.8, 10.1, 6.7 Hz, 1 H), 5.09–4.88 (m, 2 H), 4.66–4.48 (m, 2 H), 4.37 (d, J = 17.2 Hz, 2 H), 4.14 (d, J = 17.2 Hz, 2 H), 3.82–3.70 (m, 1 H), 3.26–3.06 (m, 2 H), 2.51 (s, 3 H), 2.20–1.86 (m, 4 H), 1.83–1.53 (m, 2 H), 1.39 (s, 4 H), 1.30 (t, J = 7.1 Hz, 3 H).
13C NMR (101 MHz, DMSO-d 6): δ = 213.74, 199.26, 169.24, 138.57, 136.81, 132.73, 126.90, 114.79, 70.04, 61.93, 50.42, 47.62, 35.29, 33.38, 32.93, 27.98, 27.90, 25.74, 13.46.
HRMS (EI+): m/z calcd for C24H33BNO6S2 +: 506.1836; found: 506.1854.
#
4-(4-((Ethoxycarbonothioyl)thio)-4-(6-methyl-4,8-dioxo-1,3,6,2-dioxazaborocan-2-yl)butanoyl)phenylboronate Pinacol Ester (14)
Xan-Bpin (293.0 mg, 0.8 mmol), vinylboronate MIDA ester (92.0 mg, 0.5 mmol), and DLP (64.0 mg, 0.16 mmol) were dissolved in EA (2.0 mL), and the solution was stirred at 85 °C for 3 h. Crude product was purified by acidified flash chromatography (PE/EA, 4:1).
Yield: 176 mg (64%); white solid; mp 95–96 °C.
IR (neat): 1765, 1680, 1508, 1450, 1398, 1357, 1276, 1211, 1142, 1088, 1032, 985, 961, 856, 822, 652 cm–1.
1H NMR (400 MHz, DMSO-d 6): δ = 7.90 (d, J = 8.4 Hz, 2 H), 7.80 (d, J = 8.3 Hz, 2 H), 4.61–4.43 (m, 2 H), 4.33 (dd, J = 27.7, 17.3 Hz, 2 H), 4.11 (dd, J = 31.6, 17.3 Hz, 2 H), 3.45 (dd, J = 8.3, 4.1 Hz, 1 H), 3.25–3.12 (m, 1 H), 3.05 (m, 1 H), 2.98 (s, 3 H), 2.31–2.20 (m, 1 H), 1.84 (m, 1 H), 1.33–1.26 (m, 15 H).
13C NMR (101 MHz, DMSO-d 6): δ = 214.68, 199.56, 168.43, 168.30, 138.63, 134.64, 126.90, 84.03, 70.47, 62.87, 62.70, 46.06, 35.94, 25.90, 24.63, 13.44.
HRMS (EI+): m/z calcd for C24H34B2NO8S2 +: 550.1906; found: 550.1926.
#
Boron-Containing Pyrroles 15–21; General Procedure
To a solution of xanthate adduct 12a/12b (1 equiv) in dioxane were added p-toluenesulfonic acid monohydrate (0.2–0.6 equiv) and the corresponding amine (1.1–4.0 equiv). The reaction mixture was stirred at 100 °C in a sealed bottle for 1 h, and then the solvent was evaporated under reduced pressure. There was a pungent smell in the bottle after the reaction. The residue was purified by chromatography on silica gel directly. All silica gel used here was not treated.
#
4-(1-Benzyl-1H-pyrrol-2-yl)phenylboronate MIDA Ester (15a)
Xanthate adduct 12a (157 mg, 0.3 mmol), benzylamine (48 mg, 0.45 mmol), and p-toluenesulfonic acid monohydrate (11 mg, 0.06 mmol) were dissolved in dioxane (1.6 mL). The sealed reaction mixture was stirred at 100 °C for 1 h, followed by evaporation of the solvent under reduced pressure. Crude product was purified by flash chromatography (PE/EA, 1:4).
Yield: 58 mg (50%); yellow solid; mp 85–87 °C.
IR (neat): 1759, 1607, 1453, 1334, 1284, 1219, 1192, 1035, 985, 888, 866, 828, 799, 717, 697 cm–1.
1H NMR (400 MHz, DMSO-d 6): δ = 7.40 (d, J = 8.2 Hz, 2 H), 7.33–7.29 (m, 2 H), 7.29–7.16 (m, 3 H), 6.98–6.90 (m, 3 H), 6.23 (dd, J = 3.6, 1.8 Hz, 1 H), 6.17 (dd, J = 3.5, 2.8 Hz, 1 H), 5.24 (s, 2 H), 4.32 (d, J = 17.2 Hz, 2 H), 4.11 (d, J = 17.1 Hz, 2 H), 2.50 (s, 3 H).
13C NMR (101 MHz, DMSO-d 6): δ = 169.31, 139.13, 133.70, 133.32, 132.53, 128.42, 127.20, 127.03, 126.19, 124.00, 109.05, 108.14, 61.73, 50.11, 47.52.
HRMS (EI+): m/z calcd for C22H22BN2O4 +: 389.1667; found: 389.1679.
#
4-(1-Benzyl-1H-pyrrol-2-yl)phenylboronate Pinacol Ester (15b)
Xanthate adduct 12b (148 mg, 0.3 mmol), benzylamine (64 mg, 0.6 mmol), and p-toluenesulfonic acid monohydrate (38 mg, 0.2 mmol) were dissolved in dioxane (1.6 mL). The sealed reaction mixture was stirred at 100 °C for 1 h, followed by evaporation of the solvent under reduced pressure. Crude product was purified by flash chromatography (PE/Et2O, 95:5).
Yield: 96 mg (89%); white solid; mp 107–108 °C.
IR (neat): 1608, 1496, 1452, 1393, 1354, 1321, 1304, 1263, 1140, 1090, 1070, 1018, 961, 857, 845, 729, 718, 698, 656 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.78 (d, J = 8.2 Hz, 2 H), 7.34 (d, J = 8.3 Hz, 2 H), 7.32–7.21 (m, 3 H), 7.06–6.99 (m, 2 H), 6.77 (dd, J = 2.7, 1.8 Hz, 1 H), 6.30 (m, 2 H), 5.16 (s, 2 H), 1.34 (s, 12 H).
13C NMR (101 MHz, CDCl3): δ = 138.73, 135.95, 134.89, 134.84, 128.67, 127.91, 127.33, 126.43, 123.50, 109.38, 108.67, 83.79, 50.80, 24.88.
HRMS (EI+): m/z calcd for C23H27BNO2 +: 360.2129; found: 360.2138.
#
4-(1-Cyclohexyl-1H-pyrrol-2-yl)phenylboronate MIDA Ester (16a)
Xanthate adduct 12a (209 mg, 0.4 mmol), cyclohexylamine (99 mg, 1 mmol), and p-toluenesulfonic acid monohydrate (38 mg, 0.2 mmol) were dissolved in dioxane (2 mL). The sealed reaction mixture was stirred at 100 °C for 1 h, followed by evaporation of the solvent under reduced pressure. Crude product was purified by flash chromatography (PE/EA, 2:3).
Yield: 62 mg (44%); colorless oil.
IR (neat): 1731, 1659, 1375, 1245, 1050, 1023, 1003, 822, 759, 672, 614 cm–1.
1H NMR (400 MHz, DMSO-d 6): δ = 7.49 (d, J = 7.6 Hz, 2 H), 7.31 (d, J = 7.6 Hz, 2 H), 7.02 (s, 1 H), 6.07 (d, J = 24.5 Hz, 2 H), 4.36 (d, J = 17.3 Hz, 2 H), 4.15 (d, J = 17.2 Hz, 2 H), 3.98 (t, J = 11.7 Hz, 1 H), 2.57 (s, 3 H), 2.00–1.54 (m, 6 H), 1.35–1.06 (m, 4 H).
13C NMR (101 MHz, DMSO-d 6): δ = 169.36, 133.74, 132.93, 132.66, 127.67, 118.83, 107.99, 107.82, 61.75, 54.69, 47.54, 34.21, 25.43, 24.76.
HRMS (EI+): m/z calcd for C21H26BN2O4 +: 381.1980; found: 381.1991.
#
4-(1-Cyclohexyl-1H-pyrrol-2-yl)phenylboronate Pinacol Ester (16b)
Xanthate adduct 12b (247 mg, 0.5 mmol), cyclohexylamine (99 mg, 1.0 mmol), and p-toluenesulfonic acid monohydrate (48 mg, 0.25 mmol) were dissolved in dioxane (2 mL). The sealed reaction mixture was stirred at 100 °C for 1 h, followed by evaporation of the solvent under reduced pressure. Crude product was purified by flash chromatography (PE/Et2O, 97:3).
Yield: 142.1 mg (81%); white solid; mp 68–70 °C.
IR (neat): 1607, 1396, 1370, 1358, 1324, 1264, 1140, 1092, 1068, 858, 844, 737, 717, 674, 657 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.85 (d, J = 8.1 Hz, 2 H), 7.36 (d, J = 8.1 Hz, 2 H), 6.89 (dd, J = 2.7, 1.9 Hz, 1 H), 6.33–6.11 (m, 2 H), 4.05 (m, 1 H), 2.00 (d, J = 11.5 Hz, 2 H), 1.82 (d, J = 11.9 Hz, 2 H), 1.75–1.55 (m, 4 H), 1.37 (s, 12 H), 1.31–1.11 (m, 2 H).
13C NMR (101 MHz, CDCl3): δ = 200.07, 138.79, 134.92, 127.01, 84.20, 70.41, 37.08, 36.51, 25.19, 24.88, 13.77.
HRMS (EI+): m/z calcd for C22H31BNO2 +: 352.2442; found: 352.2452.
#
4-(1-(Furan-2-ylmethyl)-1H-pyrrol-2-yl)phenylboronate MIDA Ester (17a)
Xanthate adduct 12a (261 mg, 0.5 mmol), furfurylamine (97 mg, 1 mmol), and p-toluenesulfonic acid monohydrate (19 mg, 0.1 mmol) were dissolved in dioxane (2 mL). The sealed reaction mixture was stirred at 100 °C for 1 h, followed by evaporation of the solvent under reduced pressure. Crude product was purified by flash chromatography (PE/EA, 5:1).
Yield: 114 mg (60%); yellow solid; mp 85–87 °C.
IR (neat): 1758, 1608, 1461, 1335, 1285, 1219, 1192, 1148, 1034, 987, 885, 867, 829, 792, 710, 691, 647 cm–1.
1H NMR (400 MHz, DMSO-d 6): δ = 7.58 (dd, J = 1.9, 0.9 Hz, 1 H), 7.51–7.46 (m, 2 H), 7.44–7.39 (m, 2 H), 6.89 (dd, J = 2.8, 1.8 Hz, 1 H), 6.37 (dd, J = 3.2, 1.9 Hz, 1 H), 6.19–6.14 (m, 2 H), 6.12 (dd, J = 3.5, 2.8 Hz, 1 H), 5.15 (s, 2 H), 4.35 (d, J = 17.2 Hz, 2 H), 4.14 (d, J = 17.1 Hz, 2 H), 2.54 (s, 3 H).
13C NMR (101 MHz, DMSO-d 6): δ = 169.36, 151.20, 142.79, 133.58, 133.12, 132.60, 127.48, 123.17, 110.52, 108.76, 108.16, 108.06, 61.74, 47.55, 43.26, 30.66.
HRMS (EI+): m/z calcd for C20H20BN2O5 +: 379.1460; found: 379.1470.
#
4-(1-(Furan-2-ylmethyl)-1H-pyrrol-2-yl)phenylboronate Pinacol Ester (17b)
Xanthate adduct 12b (296 mg, 0.6 mmol), furfurylamine (145 mg, 1.5 mmol), and p-toluenesulfonic acid monohydrate (57 mg, 0.3 mmol) were dissolved in dioxane (2.5 mL). The sealed reaction mixture was stirred at 100 °C for 1 h, followed by evaporation of the solvent under reduced pressure. Crude product was purified by flash chromatography (PE/Et2O, 97:3).
Yield: 174 mg (84%); white solid; mp 107–109 °C.
IR (neat): 1608, 1500, 1468, 1397, 1358, 1326, 1140, 1093, 1080, 1069, 1015, 962, 908, 850, 819, 800, 745, 729, 716, 654 cm–1.
1H NMR (400 MHz, CDCl3): δ = 8.19 (d, J = 8.3 Hz, 2 H), 7.77 (d, J = 8.3 Hz, 2 H), 7.70 (dd, J = 1.9, 0.9 Hz, 1 H), 7.18 (dd, J = 2.6, 1.9 Hz, 1 H), 6.64 (dd, J = 3.2, 1.9 Hz, 1 H), 6.59 (dd, J = 2.3, 1.7 Hz, 2 H), 6.46 (dd, J = 3.2, 0.8 Hz, 1 H), 5.39 (s, 2 H), 1.70 (s, 12 H).
13C NMR (101 MHz, CDCl3): δ = 151.14, 142.53, 135.79, 134.88, 134.60, 128.18, 122.99, 110.37, 109.28, 108.69, 108.01, 83.84, 43.93, 24.90.
HRMS (EI+): m/z calcd for C21H25BNO3 +: 350.1922; found: 350.1916.
#
4-(1H-Pyrrol-2-yl)phenylboronate Pinacol Ester (18b)
Xanthate adduct 12b (247 mg, 0.5 mmol), ammonium acetate (185 mg, 2.4 mmol), and p-toluenesulfonic acid monohydrate (48 mg, 0.25 mmol) were dissolved in dioxane (3 mL). The sealed reaction mixture was stirred at 100 °C for 1 h, followed by evaporation of the solvent under reduced pressure. Crude product was purified by flash chromatography (PE/Et2O, 95:5).
Yield: 94 mg (70%); unstable white solid.
IR (neat): 1701, 1606, 1357, 1317, 1300, 1269, 1139, 1120, 1106, 1086, 1031, 1014, 962, 916, 856, 807, 739, 668, 653 cm–1.
1H NMR (400 MHz, CDCl3): δ = 8.54 (s, 1 H), 7.80 (d, J = 8.3 Hz, 2 H), 7.48 (d, J = 8.3 Hz, 2 H), 6.88 (td, J = 2.7, 1.5 Hz, 1 H), 6.60 (m, J = 1.5 Hz, 1 H), 6.31 (dt, J = 3.5, 2.6 Hz, 1 H), 1.36 (s, 12 H).
13C NMR (101 MHz, CDCl3): δ = 135.43, 135.17, 131.94, 122.82, 119.32, 110.32, 106.76, 83.78, 24.89.
HRMS (EI+): m/z calcd for C16H21BNO2 +: 270.1660; found: 270.1673.
#
4-(1-Phenyl-1H-pyrrol-2-yl)phenylboronate Pinacol Ester (19b)
Xanthate adduct 12b (494 mg, 1 mmol), aniline (930 mg, 10 mmol), and p-toluenesulfonic acid monohydrate (95 mg, 0.5 mmol) were dissolved in dioxane (3 mL). The sealed reaction mixture was stirred at 100 °C for 5 d, followed by evaporation of the solvent under reduced pressure. Crude product was purified by flash chromatography (PE/Et2O, 97:3).
Yield: 231 mg (67%); white solid; mp 147–148 °C.
IR (neat): 1609, 1495, 1458, 1398, 1361, 1332, 1139, 1100, 1037, 859, 845, 762, 724, 670, 650 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.68–7.60 (m, 2 H), 7.30 (m, 3 H), 7.17 (dd, J = 6.9, 1.6 Hz, 2 H), 7.13 (d, J = 8.2 Hz, 2 H), 6.95 (dd, J = 2.7, 1.8 Hz, 1 H), 6.49 (dd, J = 3.6, 1.7 Hz, 1 H), 6.37 (dd, J = 3.4, 2.9 Hz, 1 H), 1.32 (s, 12 H).
13C NMR (101 MHz, CDCl3): δ = 140.51, 135.61, 134.49, 133.71, 129.07, 127.36, 126.67, 125.74, 124.92, 111.22, 109.39, 83.73, 24.88.
HRMS (EI+): m/z calcd for C22H25BNO2 +: 346.1973; found: 346.1981.
#
4-(1-(4-Bromophenyl)-1H-pyrrol-2-yl)phenylboronate Pinacol Ester (20b)
Xanthate adduct 12b (247 mg, 0.5 mmol), 4-bromoaniline (1.03 g, 6 mmol), and p-toluenesulfonic acid monohydrate (45 mg, 0.25 mmol) were dissolved in dioxane (2 mL). The sealed reaction mixture was stirred at 100 °C for 5 d, followed by evaporation of the solvent under reduced pressure. Crude product was purified by flash chromatography (PE/Et2O, 97:3).
Yield: 169 mg (80%); white solid; mp 86–88 °C.
IR (neat): 1608, 1591, 1488, 1453, 1395, 1356, 1340, 1317, 1268, 1138, 1098, 1088, 1066, 1009, 943, 858, 830, 792, 705, 654 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.66 (d, J = 8.3 Hz, 2 H), 7.43 (d, J = 8.8 Hz, 2 H), 7.11 (d, J = 8.3 Hz, 2 H), 7.03 (d, J = 8.8 Hz, 2 H), 6.91 (dd, J = 2.8, 1.7 Hz, 1 H), 6.48 (dd, J = 3.6, 1.7 Hz, 1 H), 6.37 (dd, J = 3.6, 2.9 Hz, 1 H), 1.33 (s, 12 H).
13C NMR (101 MHz, CDCl3): δ = 139.51, 135.23, 134.61, 133.72, 132.21, 127.45, 127.14, 124.62, 120.21, 111.60, 109.84, 83.80, 24.88.
HRMS (EI+): m/z calcd for C22H24BBrNO2 +: 424.1078; found: 424.1089.
#
4-(1-Cyclopropyl-1H-pyrrol-2-yl)phenylboronate MIDA Ester (21a)
Xanthate adduct 12a (261 mg, 0.5 mmol), cyclopropylamine (114 mg, 2.0 mmol), and p-toluenesulfonic acid monohydrate (19 mg, 0.1 mmol) were dissolved in dioxane (2 mL). The sealed reaction mixture was stirred at 100 °C for 1 h, followed by evaporation of the solvent under reduced pressure. Crude product was purified by flash chromatography (PE/EA, 2:3).
Yield: 62 mg (36%); yellow solid; mp 86–88 °C.
IR (neat): 1746, 1681, 1606, 1454, 1335, 1283, 1219, 1034, 986, 887, 865, 825, 790, 704, 668, 591 cm–1.
1H NMR (400 MHz, DMSO-d 6): δ = 7.58 (d, J = 8.4 Hz, 2 H), 7.45 (d, J = 8.4 Hz, 2 H), 6.86 (dd, J = 2.7, 1.9 Hz, 1 H), 6.19 (dd, J = 3.6, 1.9 Hz, 1 H), 6.02 (dd, J = 3.6, 2.8 Hz, 1 H), 4.35 (d, J = 17.2 Hz, 2 H), 4.14 (d, J = 17.1 Hz, 2 H), 3.60–3.51 (m, 1 H), 2.55 (s, 3 H), 0.91–0.84 (m, 2 H), 0.73 (m, 2 H).
13C NMR (101 MHz, DMSO-d 6): δ = 169.38, 134.30, 133.62, 132.31, 126.76, 122.91, 108.65, 107.31, 61.73, 47.52, 29.50, 8.09.
HRMS (EI+): m/z calcd for C18H20BN2O4 +: 339.1511; found: 339.1521.
#
4-(1-Cyclopropyl-1H-pyrrol-2-yl)phenylboronate Pinacol Ester (21b)
Xanthate adduct 12b (247 mg, 0.5 mmol), cyclopropylamine (114 mg, 2 mmol), and p-toluenesulfonic acid monohydrate (45 mg, 0.25 mmol) were dissolved in dioxane (2 mL). The sealed reaction mixture was stirred at 100 °C for 1 h, followed by evaporation of the solvent under reduced pressure. Crude product was purified by flash chromatography (PE/Et2O, 4:1).
Yield: 132 mg (86%); white solid; mp 69–71 °C.
IR (neat): 1608, 1454, 1395, 1357, 1317, 1262, 1140, 1102, 1088, 1018, 858, 841, 828, 783, 744, 708, 656 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.82 (d, J = 8.3 Hz, 2 H), 7.57 (d, J = 8.3 Hz, 2 H), 6.82 (dd, J = 2.7, 1.9 Hz, 1 H), 6.28 (dd, J = 3.6, 1.9 Hz, 1 H), 6.15 (dd, J = 3.6, 2.8 Hz, 1 H), 3.47 (m, 1 H), 1.37 (s, 12 H), 0.95–0.74 (m, 4 H).
13C NMR (101 MHz, CDCl3): δ = 136.32, 135.19, 134.61, 127.29, 123.35, 109.27, 107.68, 83.77, 29.78, 24.91, 8.41.
HRMS (EI+): m/z calcd for C19H25BNO2 +: 310.1973; found: 310.1982.
#
4-(Thiophen-2-yl)phenylboronate Pinacol Ester (22)
The reaction was performed in a sealed microwave tube. To a solution of xanthate adduct 12b (247 mg, 0.5 mmol) in acetic acid (1 mL) was added potassium iodide (232 mg, ca. 1.4 mmol). The suspension was heated under microwave irradiation to 140 °C for 4 h. After cooling to r.t., the suspension was taken for flash chromatography (PE/Et2O, 98:2).
Yield: 103 mg (72%); off-white solid; mp 61–63 °C.
IR (neat): 1605, 1396, 1356, 1320, 1301, 1262, 1211, 1140, 1090, 1016, 961, 857, 818, 740, 701, 669, 652 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.86–7.79 (m, 2 H), 7.68–7.59 (m, 2 H), 7.38 (dd, J = 3.6, 1.2 Hz, 1 H), 7.31 (dd, J = 5.1, 1.1 Hz, 1 H), 7.09 (dd, J = 5.1, 3.6 Hz, 1 H), 1.36 (s, 12 H).
13C NMR (101 MHz, CDCl3): δ = 144.28, 136.92, 135.39, 128.11, 125.35, 125.06, 123.63, 83.86, 24.90.
HRMS (EI+): m/z calcd for C16H20BO2S+: 287.1272; found: 287.1276.
#
(5-Oxo-8-(pivaloyloxy)-5,6,7,8-tetrahydronaphthalen-2-yl)boronate MIDA Ester (23a)
To a solution of xanthate adduct 12a (802 mg, 1.5 mmol) in refluxing EA (6 mL), DLP (160 mg, 0.4 mmol) was added every hour until total consumption of starting material. TLC was used to monitor the reaction progress. After reaction completion, the solution was evaporated to remove the EA. The obtained solid was dissolved in MeCN and the solution was washed several times with PE to remove the residue of DLP. The MeCN layer was concentrated and the crude product recrystallized (EA) to obtain pure product.
Yield: 472 mg (77%); white solid; mp 233–234 °C.
IR (neat): 1759, 1712, 1682, 1478, 1452, 1281, 1236, 1182, 1149, 1042, 1032, 1018, 1010, 892, 873, 835, 812, 790, 721, 674 cm–1.
1H NMR (400 MHz, DMSO-d 6): δ = 7.88 (d, J = 7.8 Hz, 1 H), 7.59 (d, J = 7.9 Hz, 1 H), 7.50 (s, 1 H), 6.17–5.93 (m, 1 H), 4.49–4.26 (m, 2 H), 4.21–4.06 (m, 2 H), 2.73 (t, J = 6.2 Hz, 2 H), 2.50 (s, 3 H), 2.35 (m, 1 H), 2.16 (m, 1 H), 1.17 (s, 9 H).
13C NMR (101 MHz, DMSO-d 6): δ = 196.42, 176.87, 169.27, 169.05, 140.26, 132.62, 131.78, 131.55, 125.30, 68.72, 61.90, 61.77, 47.55, 34.47, 28.02, 26.72.
HRMS (EI+): m/z calcd for C20H24BNNaO7 +: 424.1538; found: 424.1550.
#
(5-Oxo-8-(pivaloyloxy)-5,6,7,8-tetrahydronaphthalen-2-yl)boronate Pinacol Ester (23b)
To a solution of xanthate adduct 12b (494 mg, 1 mmol) in refluxing chlorobenzene (2 mL), di-tert-butyl peroxide (29.2 mg, 0.2 mmol) was added every hour until total consumption of starting material. TLC was used to monitor the reaction progress. After reaction completion, the solution was evaporated to remove as much PhCl as possible. Considering the difficulty in purification, the crude product was directly used for further reaction after being confirmed by NMR (product 23b: 50%, side product 24: 38%, calculated by 1H NMR).
Yield: 50% (calculated by 1H NMR); white solid; mp 117–119 °C (purified material).
IR (neat): 1718, 1683, 1392, 1364, 1347, 1336, 1308, 1272, 1200, 1140, 1093, 1031, 926, 852, 844, 687 cm–1.
1H NMR (400 MHz, CDCl3): δ = 8.03 (d, J = 7.8 Hz, 1 H), 7.89–7.85 (m, 1 H), 7.83 (s, 1 H), 6.10 (dd, J = 6.0, 3.8 Hz, 1 H), 2.90 (m, 1 H), 2.75–2.58 (m, 1 H), 2.49–2.17 (m, 2 H), 1.34 (s, 12 H), 1.22 (s, 9 H).
13C NMR (101 MHz, CDCl3): δ = 197.43, 177.83, 139.85, 134.97, 134.62, 133.69, 126.11, 84.33, 68.78, 39.01, 34.44, 28.34, 27.11, 24.89, 24.88.
HRMS (EI+): m/z calcd for C21H29BNaO5 +: 395.2000; found: 395.2007.
#
(5-Hydroxynaphthalen-2-yl)boronate Pinacol Ester (25)
To a solution of tetralone 23b (0.5 mmol) in toluene (3.0 mL), AlCl3 (100 mg, 0.75 mmol), Et3N (150 mg, 1.5 mmol), and Na2SO4 (200 mg) were added. The suspension was sealed in a 4-mL tube and stirred at 110 °C for 1 h. The suspension was taken for flash chromatography (PE/Et2O, 95:5).
Yield: 69 mg (51%); white solid; mp 198–200 °C.
IR (neat): 2928, 2854, 1731, 1680, 1518, 1451, 1360, 1275, 1212, 1144, 1090, 1033, 859, 825, 787, 744 cm–1.
1H NMR (400 MHz, CDCl3): δ = 8.34 (s, 1 H), 8.15 (d, J = 8.4 Hz, 1 H), 7.85 (dd, J = 8.4, 1.1 Hz, 1 H), 7.47 (d, J = 8.4 Hz, 1 H), 7.32–7.27 (m, 1 H), 6.86 (dd, J = 7.4, 0.9 Hz, 1 H), 1.40 (s, 12 H).
13C NMR (101 MHz, CDCl3): δ = 151.31, 136.01, 134.05, 129.84, 125.86, 125.75, 121.38, 120.62, 109.79, 84.04, 24.93.
HRMS (EI+): m/z calcd for C16H19BO3: 270.1652; found: 270.1658.
#
Naphthylamines 26–29; General Procedure
A solution of tetralone 23b (1 equiv) and amine (3–6 equiv) in toluene was sealed in a tube. Na2SO4 was added to the tube for removing the formed water. The solution was stirred at 110 °C for 2 h. Then, AlCl3 was added and the suspension was heated for another 1 h at 110 °C. After cooling to r.t., the suspension was taken for flash chromatography to obtain the target product. Both acidifying the silica gel or adding Et3N to the eluent could make the product adsorbed more easily on silica gel. However, some product was still adsorbed even using untreated silica gel.
#
(5-(Cyclopropylamino)naphthalen-2-yl)boronate Pinacol Ester (26)
Tetralone 23b (0.5 mmol) and cyclopropylamine (171 mg, 3 mmol) were dissolved in toluene (2 mL) and Na2SO4 (500 mg) was added. After being stirred at 110 °C for 2 h, AlCl3 (200 mg) was added and the suspension was heated for another 1 h at 110 °C. The suspension was taken for flash chromatography (PE/Et2O, 98:2).
Yield: 106 mg (69%); off-white paste colloid.
IR (neat): 1712, 1513, 1457, 1357, 1285, 1270, 1218, 1142, 1089, 1021, 963, 857, 824, 658 cm–1.
1H NMR (400 MHz, CDCl3): δ = 8.31 (s, 1 H), 7.77 (dd, J = 8.5, 1.3 Hz, 1 H), 7.70 (d, J = 8.5 Hz, 1 H), 7.39 (dd, J = 8.1, 7.5 Hz, 1 H), 7.32 (d, J = 8.2 Hz, 1 H), 7.10 (dd, J = 7.4, 1.2 Hz, 1 H), 4.90 (s, 1 H), 2.60–2.52 (m, 1 H), 1.39 (s, 12 H), 0.87–0.79 (m, 2 H), 0.69–0.60 (m, 2 H).
13C NMR (101 MHz, CDCl3): δ = 143.73, 137.00, 133.45, 129.34, 126.47, 124.66, 118.85, 118.51, 106.84, 83.91, 25.50, 24.95, 7.52.
HRMS (EI+): m/z calcd for C19H25BNO2 +: 310.1973; found: 310.1979.
#
(5-((4-Bromophenyl)amino)naphthalen-2-yl)boronate Pinacol Ester (27)
Tetralone 23b (0.5 mmol) and 4-bromoaniline (344 mg, 2 mmol) were dissolved in toluene (3 mL) and Na2SO4 (200 mg) was added. After being stirred at 110 °C for 2 h, AlCl3 (100 mg) was added and the suspension was heated for another 1 h at 110 °C. The suspension was taken for flash chromatography (PE/Et2O, 9:1).
Yield: 68 mg (32%); yellow paste colloid.
IR (neat): 3374, 2975, 1726, 1591, 1570, 1512, 1488, 1467, 1370, 1352, 1325, 1300, 1271, 1141, 1096, 1072, 963, 861, 850, 813, 794, 686 cm–1.
1H NMR (400 MHz, CDCl3): δ = 8.40 (s, 1 H), 7.95 (d, J = 8.5 Hz, 1 H), 7.83 (dd, J = 8.5, 1.2 Hz, 1 H), 7.67–7.63 (m, 1 H), 7.43–7.35 (m, 2 H), 7.35–7.28 (m, 2 H), 6.86–6.78 (m, 2 H), 5.92 (s, 1 H), 1.40 (s, 12 H).
13C NMR (101 MHz, CDCl3): δ = 144.12, 137.93, 136.91, 134.03, 132.14, 130.52, 129.50, 125.92, 124.50, 120.96, 118.47, 117.93, 111.99, 84.06, 24.96.
HRMS (EI+): m/z calcd for C22H24BBrNO2 +: 424.1078; found: 424.1069.
#
(5-(Cyclohexylamino)naphthalen-2-yl)boronate Pinacol Ester (28)
Tetralone 23b (0.5 mmol) and cyclohexylamine (150 mg, 1.5 mmol) were dissolved in toluene (3 mL) and Na2SO4 (200 mg) was added. After being stirred at 110 °C for 2 h, AlCl3 (100 mg) was added and the suspension was heated for another 1 h at 110 °C. The suspension was taken for flash chromatography (PE/Et2O, 95:5).
Yield: 82 mg (47%); yellow paste colloid.
IR (neat): 1712, 1513, 1457, 1357, 1324, 1286, 1217, 1140, 1088, 1021, 963, 858, 826, 658 cm–1.
1H NMR (400 MHz, CDCl3): δ = 8.29 (s, 1 H), 7.75 (s, 2 H), 7.32 (t, J = 7.9 Hz, 1 H), 7.23 (d, J = 7.9 Hz, 1 H), 6.66 (d, J = 7.4 Hz, 1 H), 3.47 (dt, J = 13.8, 6.5 Hz, 1 H), 2.19 (d, J = 9.9 Hz, 2 H), 1.90–1.77 (m, 2 H), 1.64 (dd, J = 48.7, 16.5 Hz, 4 H), 1.46–1.31 (m, 14 H).
13C NMR (101 MHz, CDCl3): δ = 142.22, 137.09, 133.81, 129.11, 126.51, 125.54, 124.86, 118.93, 117.36, 105.69, 83.88, 51.85, 33.29, 26.06, 25.10, 24.94.
HRMS (EI+): m/z calcd for C22H31BNO2 +: 352.2442; found: 352.2440.
#
(5-((Furan-2-ylmethyl)amino)naphthalen-2-yl)boronate Pinacol Ester (29)
Tetralone 23b (0.5 mmol) and furfurylamine (194 mg, 2 mmol) were dissolved in toluene (3 mL) and Na2SO4 (300 mg) was added. After being stirred at 110 °C for 2 h, AlCl3 (100 mg) was added and the suspension was heated for another 1 h at 110 °C. The suspension was taken for flash chromatography (PE/Et2O, 9:1).
Yield: 101 mg (58%); yellow paste colloid.
IR (neat): 1726, 1518, 1371, 1356, 1327, 1274, 1142, 1119, 1088, 1012, 964, 855, 744, 686 cm–1.
1H NMR (400 MHz, CDCl3): δ = 8.32 (s, 1 H), 7.80 (s, 2 H), 7.42 (dd, J = 1.8, 0.9 Hz, 1 H), 7.34 (m, 2 H), 6.73 (dd, J = 6.6, 2.0 Hz, 1 H), 6.35 (ddd, J = 4.0, 3.2, 1.3 Hz, 2 H), 4.49 (s, 2 H), 1.40 (s, 12 H).
13C NMR (101 MHz, CDCl3): δ = 152.35, 142.66, 142.14, 137.00, 133.54, 129.56, 126.36, 125.09, 119.09, 118.86, 110.45, 107.40, 105.93, 83.94, 41.72, 24.95.
HRMS (EI+): m/z calcd for C21H25BNO3 +: 350.1922; found: 350.1916.
#
(6-Bromo-5-oxo-8-(pivaloyloxy)-5,6,7,8-tetrahydronaphthalen-2-yl)boronate MIDA Ester (30)
To a solution of tetralone 23a (401.0 mg, 1 mmol) and acetic acid (120 mg, 2 mmol) in MeCN (4 mL), N-bromosuccinimide (196 mg, 1.1 mmol) was added slowly at 0 °C. Upon finishing the addition, the solution was warmed to r.t. and stirred for 4 h. Then, the reaction solution was taken for flash chromatography (PE/EA, 2:3).
Yield: 196 mg (41%); brown oil.
IR (neat): 1760, 1721, 1682, 1280, 1239, 1148, 1038, 1003, 989, 961, 891, 873, 843, 817, 772 cm–1.
1H NMR (400 MHz, (CD3)2CO): δ = 8.03 (d, J = 7.8 Hz, 1 H), 7.77–7.72 (m, 1 H), 7.67 (s, 1 H), 6.34 (dd, J = 8.0, 4.8 Hz, 1 H), 5.09–5.04 (m, 1 H), 4.43 (dd, J = 17.1, 11.2 Hz, 2 H), 4.21 (dd, J = 20.3, 17.1 Hz, 2 H), 2.89–2.71 (m, 5 H), 1.25 (s, 9 H).
13C NMR (101 MHz, (CD3)2CO): δ = 189.88, 177.96, 169.19, 168.92, 141.01, 133.85, 132.28, 130.48, 127.90, 68.22, 62.97, 62.81, 48.71, 48.37, 39.49, 38.42, 27.37.
HRMS (EI+): m/z calcd for C20H23BBrNNaO7 +: 502.0643; found: 502.0640.
#
#
Conflict of Interest
The authors declare no conflict of interest.
Supporting Information
- Supporting information for this article is available online at https://doi-org.accesdistant.sorbonne-universite.fr/10.1055/a-2314-1877.
- Supporting Information
-
References
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Corresponding Authors
Publication History
Received: 21 March 2024
Accepted after revision: 25 April 2024
Accepted Manuscript online:
25 April 2024
Article published online:
21 May 2024
© 2024. Thieme. All rights reserved
Georg Thieme Verlag KG
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-
References
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- 2c Xu C, He C, Li N, Yang S, Du Y, Matyjaszewski K, Pan X. Nat. Commun. 2021; 12: 5853
- 3 Jung HS, Verwilst P, Sharma A, Shin J, Sessler JL, Kim JS. Chem. Soc. Rev. 2018; 47: 2280
- 4 Hendsbee AD, McAfee SM, Sun J.-P, McCormick TM, Hill IG, Welch GC. J. Mater. Chem. C 2015; 3: 8904
- 5a Brédas J.-L, Beljonne D, Coropceanu V, Cornil J. Chem. Rev. 2004; 104: 4971
- 5b Murphy AR, Fréchet JM. J. Chem. Rev. 2007; 107: 1066
- 5c Mdluli SB, Ramoroka ME, Yussuf ST, Modibane KD, John-Denk VS, Iwuoha EI. Polymers 2022; 14: 716
- 5d Kertesz M, Choi CH, Yang S. Chem. Rev. 2005; 105: 3448
- 5e Zhen X, Pu K, Jiang X. Small 2021; 17: e2004723
- 6a Nanjo T, Matsugasako T, Maruo Y, Takemoto Y. Org. Lett. 2022; 24: 359
- 6b Guo H.-M, He B.-Q, Wu X. Org. Lett. 2022; 24: 3199
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- 6d López-Mendoza P, Miranda LD. Org. Biomol. Chem. 2020; 18: 3487
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- 7b Quiclet-Sire B, Zard SZ. Pure Appl. Chem. 2011; 83: 519
- 8 Zard SZ. Tetrahedron 2020; 76: 130802
- 9 Quiclet-Sire B, Zard SZ. Synlett 2017; 28: 2685
- 10a Jullien H, Quiclet-Sire B, Tetart T, Zard SZ. Org. Lett. 2014; 16: 302
- 10b Huang G, Li J, Li J, Li J, Sun M, Zhou P, Chen L, Huang Y, Jiang S, Li Y. J. Org. Chem. 2020; 85: 13037
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- 11d Zhang Z, Gevorgyan V. Org. Lett. 2020; 22: 8500
- 11e Zhou T, Chen H, Liu Y, Wang H, Yan Q, Wang W, Chen F. J. Org. Chem. 2022; 87: 15582
- 11f Muthupandi P, Sundaravelu N, Sekar G. J. Org. Chem. 2017; 82: 1936
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