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DOI: 10.1055/a-2063-0221
An Intramolecular Radical C–N Coupling by N-Iodosuccinimide
S.K.B. and R.B. thank DST (INSPIRE) and CSIR (India) for fellowships.
Abstract
A useful method for the formation of benzimidazole-fused phenanthridines through an intramolecular coupling of unactivated C(sp2)–H and N(sp3)–H bonds using N-iodosuccinimide (NIS) in trifluoroethanol (TFE) is presented. The synthesis of benzo[4,5]imidazo[1,2-f]phenanthridines from 2-([1,1′-biphenyl]-2-yl)-1H-benzo[d]imidazole derivatives is mild, efficient, and sustainable, with high yields and minimal waste generation. The control experiments and EPR studies were aimed at rationalizing the radical pathway of the reaction. Specifically, the use of 1,1-diphenylethylene, TEMPO, BHT, and DMPO as a free-radical spin-trapping reagent in EPR studies, allowed us to conceive a radical pathway. The gram-scale synthesis further supported the practical utility of the methodology for the field of synthetic chemistry.
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Key words
benzimidazole-fused phenanthridines - C–N coupling - TFE - N-iodosuccinimide - radical cyclizationThe development of sustainable synthetic methods for the production of Active Pharmaceutical Ingredients (APIs)[1] and other materials is becoming increasingly important due to the need for environmentally friendly and cost-effective manufacturing processes. By adopting atom- and step-economical approaches, synthetic chemists can minimize waste, reduce the use of hazardous reagents, and optimize reaction conditions to improve yields and selectivity.[2] The use of metal-free techniques in organic synthesis has gained significant attention in recent years due to several reasons. One of the main reasons is the concern over the toxicity of transition metals and their potential environmental impact. In addition, metal-free techniques are often cheaper and more accessible than transition-metal-catalyzed methods.[3] The metal-free techniques in organic synthesis include a range of reactions such as the use of organocatalysis,[4] photoredox catalysis,[5] and biocatalysis.[6]
Nitrogenous compounds are prevalent in many biologically active molecules, including pharmaceuticals,[7] natural products,[8] and synthetic intermediates.[9] Therefore, developing efficient and selective methodologies for the formation of C–N bonds is of great importance to synthetic chemistry and pharmaceutical industry.[10] Cross-coupling reactions,[11] such as the Suzuki–Miyaura[12] and Buchwald–Hartwig reactions,[13] are powerful methods for the formation of C–N bonds.[14] In the current context, N-iodosuccinimide (NIS) is a mild and versatile oxidizing agent that has been widely used in organic synthesis for the generation of heterocyclic scaffolds.[15]
Benzimidazole-fused phenanthridines are a class of heterocyclic compounds that consist of a core structure composed of benzimidazole, quinolinone, and isoquinoline scaffolds. These compounds have unique electronic and structural properties that make them useful in a range of applications in pharmaceutical chemistry and material science.[16] In material science, benzimidazole-fused phenanthridines have been studied for their electroluminescent properties (Scheme [1a]).[17] The Pd(II)-catalyzed intermolecular C–H arylation of 2-arylbenzimidazoles followed by an intramolecular N-arylation reaction is a commonly used method for synthesizing benzimidazole-fused phenanthridines.[18] Mal and co-workers developed two methods for the synthesis of benzimidazole-fused phenanthridines, including a radical-mediated catalyst-free photoinduced intramolecular C–N cross-coupling reaction (Scheme [1b])[19] and an iodine(III) reagent PIFA [phenyliodine bis(trifluoroacetate)]-mediated C–N coupling.[20] However, the work reported herein (Scheme [1c]), is an intramolecular radical C–N coupling reaction mediated by N-iodosuccinimide (NIS) in trifluoroethanol (TFE). In this reaction, the unactivated C(sp2)–H bond and N(sp3)–H bond of 2-([1,1′-biphenyl]-2-yl)-1H-benzo[d]imidazoles undergo a coupling reaction, resulting in an intramolecular radical C–N coupling and subsequent cyclization to form the benzo[4,5]imidazo[1,2-f]phenanthridine. When hypervalent iodine reagents like NIS is used in TFE,[9] [21] it can increase the solubility of NIS, allowing for better contact between the reagent and the substrate. Additionally, TFE can act as a hydrogen bond donor, which can stabilize reactive intermediates and transition states during the reaction.[22]
a Reaction conditions: 1a (0.294 mmol) and NIS (0.589 mmol, 2 equiv) in TFE (2.0 mL) at rt for 22 h.
b Yield of the isolated product after purification by silica gel column chromatography.
Towards the optimization of the reaction condition, 2-([1,1′-biphenyl]-2-yl)-5,6-dichloro-1H-benzo[d]imidazole (1a) was used as a model substrate (Table [1]). Initially, 1.0 equivalent of NIS was used in TFE, and the cyclized product 2a was obtained in 77% yield (Table [1], entry 1). Increasing the equivalent of NIS from 1.0 to 1.5 equivalents led to an increase in the yield of the desired product from 77 to 88% (entry 2). The maximum yield of 97% was obtained when 2 equivalents of NIS was used as an oxidant in TFE for 22 hours (entry 3). 1,1,1,3,3,3-Hexafluoroisopropyl alcohol (HFIP) showed similar efficiency to TFE and delivered 92% of the cyclized product (entry 4). Several non-fluorinated solvents, including MeCN (acetonitrile), DCE (1,2-dichloroethane), DCM (dichloromethane), THF (tetrahydrofuran), EtOH (ethanol), DMF (N,N-dimethylformamide), 1,4-dioxane, nitromethane, etc. were screened, but none of them produced superior results compared to TFE (entries 5–12). No product formation was identified when molecular iodine was used as an oxidant (entry 13). The oxidants NBS and NCS produced 2a in 88% and 61% yield, respectively (entries 14, 15). However, the reaction failed with tetra-butylammonium iodide in TFE (entry 16). The optimized condition was identified as: use of 0.294 mmol of 1a and 0.589 mmol of NIS (2 equiv) in 2.0 mL TFE at room temperature for 22 hours to isolate 2a in 97% yield.
Various substituted benzimidazole derivatives were successfully converted to their corresponding products in high yields, demonstrating the broad substrate scope of the reaction (Schemes 2 and 3). Additionally, symmetrically di-substituted benzimidazole derivatives were converted to their corresponding products as single isomers, indicating high regioselectivity in the reaction. The cyclized product 2a was isolated in 97% yield, indicating the high efficiency of the intramolecular radical C–N coupling reaction. We also observed the successful conversion of various substituted 5,6-dichlorobenzimidazoles to their corresponding benzimidazole-fused phenanthridine products 2b–f in good yields, including derivatives with electron-donating (methyl, ethyl, tert-butyl) and electron-withdrawing (fluoro, trifluoromethyl) groups at the aryl moiety. The 5,6-dichlorobenzimidazoles with fluoro substitution in the biphenyl moiety successfully produced 2g in a high yield of 96%. Moreover, unsubstituted benzimidazoles with fluoro, acetyl (COCH3), and methoxy (OMe) group at the p-position of aryl moiety were also efficiently converted to the corresponding products 2i–k in good yields. However, o-substituted aryl moiety containing benzimidazole 1l was smoothly converted to 2l in 86% yield. The unsubstituted aryl skeleton of benzimidazoles 1h also produced the expected product 2h in a high yield of 94%. Similarly, 5,6-dimethylbenzimidazole with the unsubstituted aryl skeleton 1m was successfully cyclized to form product 2m with a yield of 95%. Similarly, 5,6-dimethylbenzimidazoles with tert-butyl, fluoro, CF3, and chloro group at the aryl moiety also produced the corresponding products 2n–2q in excellent yields. 5,6-Dimethylbenzimidazoles with methoxy and acetyl substitution at the biphenyl moiety resulted in the products 2r and 2s in 81% and 84% yield, respectively. The unsubstituted aryl skeleton of 5,6-difluorobenzimidazoles led to 2t with a yield of 91%. The 5,6-difluorobenzimidazoles with an ethyl group at the aryl skeleton delivered 2u with a yield of 93%.
In Scheme [3], we have examined the substrate scope of the intramolecular radical C–N coupling reaction of mono-substituted benzimidazole derivatives. The unsymmetrically substituted or mono-substituted benzimidazoles gave a mixture of regioisomers due to the possibility of forming two products: 11-substituted and 12-substituted (hetero)aryl-fused phenanthridines. However, it was observed that the bromo- and chloro-substituted benzimidazoles produced a single isomer as the major product. Contrastingly, the 3-nitro-substituted benzimidazole with an unsubstituted biphenyl moiety produced regioisomeric mixtures (10:3) of 2a′ in a yield of 89%. On the other hand, the 3-nitro-substituted benzimidazole with an ethyl group at the biphenyl moiety delivered 2b′ with a regioisomeric ratio of 2:1 and a yield of 92%. Similarly, 3-methyl-substituted benzimidazole having unsubstituted biphenyl moiety 1c′ also resulted in the isomeric mixtures 2c′ in a 5:2 ratio. The methyl-substituted benzimidazole bearing methyl and ethyl group at the biphenyl moiety were converted to the desired products with a mixture of regioisomers 2d′ and 2e′. The reaction using bromobenzimidazole containing ethyl, fluoro, and methyl group led to the isolation of single isomeric products with excellent yields of 2f′, 2g′, and 2h′, respectively. Similarly, chloro-substituted benzimidazoles containing electron-donating and electron-withdrawing groups attached to biphenyl moieties produced single isomer in good yields of 2i′, 2j′, and 2k′.
Control experiments were performed to understand the mechanism of the NIS-mediated cyclization reaction (Scheme [4]). The substrate 2-([1,1′-biphenyl]-2-yl)-5,6-dichloro-1-methyl-1H-benzo[d]imidazole (3a) was unreacted under the standard reaction condition (Scheme [4a]). This result indicated that the presence of the NH functional group was essential for this cyclization reaction. Furthermore, when the reaction was performed in the presence of radical scavengers such as TEMPO and BHT, no product formation was observed, as shown in Scheme [4b]. This suggests that the reaction proceeded through a radical pathway. The involvement of a radical pathway[23] was further supported by the reaction carried out using 1,1-diphenylethylene (Scheme [4b]). The EPR experiment was performed using a free-radical spin-trapping reagent DMPO (5,5-dimethyl-1-pyrroline N-oxide) under the standard reaction condition (Scheme [4c]).[24] The EPR experiment also supported the radical-based mechanism, while the reaction with highly oxidizing PIFA proceeded via an antiaromatic endocyclic nitrenium ion (Scheme [4d]).[20]
Based on literature reports[24a] [25] and control experiments, a plausible mechanism is proposed in Scheme [5]. Initially, the succinimide and iodide radicals were generated via the homolytic cleavage of N-iodosuccinimide. Then succinimide radical reacted with substrate 1a to form the radical intermediate I, which led to an intramolecular cyclization to produce intermediate II. Finally, 2a was produced via aromatization.
The synthetic application of the compound 2-bromobenzo[4,5]imidazo[1,2-f]phenanthridine (2v) is shown in Scheme [6]. The Suzuki coupling reaction of 2v with phenylboronic acid resulted in the 2-phenylbenzo[4,5]imidazo[1,2-f]phenanthridine (4) in 91% yield (Scheme [6a]). The Heck coupling of 2v and styrene delivered compound 5 in a 93% yield (Scheme [6b]). The methodology was further extended by performing the gram-scale synthesis (Scheme [6c]). Under the standard reaction condition, 3.9 mmol of 2-(4′-fluoro-[1,1′-biphenyl]-2-yl)-1H-benzo[d]imidazole (1i) and 3.35 mmol of 2-(4′-bromo-[1,1′-biphenyl]-2-yl)-1H-benzo[d]imidazole (1v) were reacted with 2.0 equivalents of NIS, leading to 2-fluorobenzo[4,5]imidazo[1,2-f]phenanthridine (2i) and 2-bromobenzo[4,5]imidazo[1,2-f]phenanthridine (2v) in 94% and 96% yield, respectively.
In summary, the described method involves the intramolecular radical C–N coupling reaction of 2-arylbenzimidazoles, which is mediated by NIS in trifluoroethanol. This reaction proceeds through the generation of a nitrogen center radical from the 2-arylbenzimidazole, which then undergoes intramolecular coupling with an N–H bond to form a new C–N bond and initiate cyclization to afford the benzimidazole-fused phenanthridine product. The method was shown to be effective for a range of substituted benzimidazole derivatives, including symmetrically di-substituted and mono-substituted derivatives, and could be used to selectively access both 11- and 12-substituted regioisomers in some cases. The use of NIS as an oxidizing agent in this reaction offers a mild and efficient alternative to other transition metal-catalyzed methods for the synthesis of (hetero)aryl-fused phenanthridine derivatives.
Commercially available reagents and solvents were used as received. Column chromatographic purifications of the compounds were performed using silica gel (mesh 230–400, 100–200) and hexane/EtOAc solvent mixtures. NMR spectra were recorded on a 400 MHz or 700 MHz instrument at 25 °C. The chemical shift values are reported in parts per million (ppm) with respect to residual CHCl3 (7.26 ppm for 1H and 77.16 ppm for 13C) or dimethyl sulfoxide (2.50 ppm for 1H and 39.52 ppm for 13C). The peak patterns are designated as follows: s: singlet; d: doublet; t: triplet; q: quartet; m: multiplet; dd: doublet of doublets; td: triplet of doublets; br s: broad singlet. The coupling constants (J) are reported in hertz (Hz).
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Preparation of 2-(4′-Bromo-[1,1′-biphenyl]-2-yl)-1H-benzo[d]imidazole (1v);[20] Typical Procedure
Step 1, Synthesis of 4′-Bromo-[1,1′-biphenyl]-2-carbaldehyde : In an oven-dried sealed tube, 2-bromobenzaldehyde (5.4 mmol), (4-bromophenyl)boronic acid (7.02 mmol, 1.3 equiv), Pd(PPh3)4 (0.27 mmol, 0.05 equiv), and K2CO3 (21.6 mmol, 4 equiv) were taken in a mixture of solvent toluene, EtOH, and H2O (9 mL + 3 mL + 6 mL) under an argon atmosphere. Then the sealed tube was immersed into a preheated oil bath at 90 °C and the reaction mixture was stirred until all the starting material was completely consumed (~12 h). Next, the mixture was diluted with brine (25 mL) and extracted with EtOAc (2 × 25 mL). The combined organic layers were collected and dried (anhyd Na2SO4). The concentrated crude product was purified by column chromatography to afford 4′-bromo-[1,1′-biphenyl]-2-carbaldehyde, which was used directly in the next step.
Step 2, Synthesis of 2-(4′-Bromo-[1,1′-biphenyl]-2-yl)-1H-benzo[d]imidazole (1v) : In a 100 mL round-bottomed flask, o-phenylenediamine (3.93 mmol, 1 equiv) and 4′-bromo-[1,1′-biphenyl]-2-carbaldehyde (3.93 mmol, 1 equiv) were taken in DMF/H2O (9:1) at rt condition. Then the reaction mixture was stirred at 80 °C (in a preheated oil bath) for 8 h. The resulting solution was cooled to rt. Then the mixture was diluted with brine (25 mL) and the aqueous layer was extracted with EtOAc. The combined organic layers were dried (anhyd Na2SO4) and concentrated under reduced pressure. The crude product was purified by column chromatography to afford the 2-(4′-bromo-[1,1′-biphenyl]-2-yl)-1H-benzo[d]imidazole (1v) in 94% yield.
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Synthesis of 2-Phenylbenzo[4,5]imidazo[1,2-f]phenanthridine (4)
In a 15 mL oven-dried sealed tube, a mixture of 2-bromobenzo[4,5]imidazo[1,2-f]phenanthridine (2v; 0.28 mmol, 1.0 equiv), phenylboronic acid (0.37 mmol, 1.3 equiv), K2CO3 (1.15 mmol, 4.0 equiv), and Pd(PPh3)4 (0.014 mmol, 16 mg) was taken in a mixture of toluene/EtOH/H2O (3:2:1) under an argon atmosphere. Then the sealed tube was immersed into a preheated oil bath at 95 °C. After 24 h, the reaction mixture was cooled to rt, diluted with brine (25 mL), and extracted with EtOAc (2 × 25 mL). The combined organic layers were dried (anhyd Na2SO4), filtered, and concentrated in vacuum. The crude product was purified by column chromatography to afford 4 in 91% yield.
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Synthesis of (E)-2-Styrylbenzo[4,5]imidazo[1,2-f]phenanthridine (5)
A 15 mL sealed tube containing a magnetic bar was charged with 2-bromobenzo[4,5]imidazo[1,2-f]phenanthridine (2v; 0.28 mmol, 1.0 equiv), styrene (0.34 mmol, 1.2 equiv), PPh3 (0.028 mmol, 7.5 mg), and Pd(OAc)2 (5 mol %, 3.2 mg) in Et3N solvent (6 mL) under an argon atmosphere. Then the reaction mixture was vigorously stirred at 95 °C. After 24 h, the mixture was cooled to rt and the solvent was evaporated in vacuum. Then the mixture was diluted with brine and EtOAc. After that, the organic layer was dried (anhyd Na2SO4). The resulting residue was purified by column chromatography to afford 5 in 93% yield.
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Synthesis of 11,12-Dichlorobenzo[4,5]imidazo[1,2-f]phenanthridine (2a); Typical Procedure
To a solution of 2-([1,1′-biphenyl]-2-yl)-5,6-dichloro-1H-benzo[d]imidazole (1a; 60 mg, 1 equiv) in TFE (1.5 mL) was added NIS (79.64 mg, 2 equiv) under open atmosphere. The reaction mixture was stirred at rt (27 °C). The progress of the reaction was monitored by TLC using EtOAc and hexane as eluent. After complete consumption of the reactant, the resulting solution was evaporated to dryness. The mixture was then quenched with aq Na2S2O3 and diluted with EtOAc (15 mL). The layers were separated, and the aqueous layer was extracted with EtOAc (2 × 15 mL). The combined organic extracts were dried (anhyd Na2SO4), filtered, and concentrated under vacuo. The crude residue was purified by silica gel column chromatography (20% EtOAc in hexane) to afford the pure product 2a; yield: 55.5 mg (93%).
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2-(2′-Methyl-[1,1′-biphenyl]-2-yl)-1H-benzo[d]imidazole (1l)
Rf = 0.50 (hexane/EtOAc 4:1); white solid; yield: 91% (196 mg); mp 145–147 °C.
1H NMR (700 MHz, DMSO-d 6): δ = 11.86 (s, 1 H), 7.80 (d, J = 7.7 Hz, 1 H), 7.56 (dt, J = 20.0, 7.0 Hz, 2 H), 7.48 (d, J = 7.0 Hz, 1 H), 7.33 (d, J = 7.0 Hz, 2 H), 7.16 (s, 1 H), 7.11 (t, J = 7.7 Hz, 4 H), 7.08 (s, 1 H), 1.93 (s, 3 H).
13C NMR (175 MHz, DMSO-d 6): δ = 151.8, 143.4, 140.7, 140.3, 135.3, 134.5, 130.8, 130.7, 130.2, 129.7, 129.6, 129.4, 127.4, 127.2, 125.4, 122.0, 121.2, 118.9, 111.3, 19.9.
IR (KBr): 3049, 2921, 1474, 1272, 1004, 956, 743 cm–1.
HRMS (ESI-TOF): m/z calcd for C20H17N2 [M + H]+: 285.1392; found: 285.1349.
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2-(4′-Bromo-[1,1′-biphenyl]-2-yl)-1H-benzo[d]imidazole (1v)
Rf = 0.50 (hexane/EtOAc 4:1); white solid; yield: 94%; mp >300 °C.
1H NMR (400 MHz, DMSO-d 6): δ = 12.20 (s, 1 H), 7.73 (dd, J = 7.6, 1.2 Hz, 1 H), 7.62 (td, J = 7.6, 1.2 Hz, 1 H), 7.55 (td, J = 7.6, 1.2 Hz, 2 H), 7.51 (d, J = 7.6 Hz, 1 H), 7.45 (s, 1 H), 7.43 (s, 1 H), 7.36 (s, 1 H), 7.18–7.12 (m, 3 H), 7.11 (s, 1 H).
13C NMR (100 MHz, DMSO-d 6): δ = 151.8, 143.5, 139.8, 139.5, 134.6, 131.2, 131.2, 131.1, 130.6, 130.2, 130.0, 127.9, 122.4, 121.5, 120.8, 119.0, 111.5.
IR (KBr): 3050, 2622, 1440, 1273, 1097, 1002, 741 cm–1.
HRMS (ESI-TOF): m/z calcd for C19H14 79BrN2 [M + H]+: 349.0340; found: 349.0353; C19H14 81BrN2 [M + H]+: 351.0340; found: 351.0320.
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11,12-Dichlorobenzo[4,5]imidazo[1,2-f]phenanthridine (2a)[19]
Rf = 0.55 (hexane/EtOAc 4:1); white solid; yield: 97% (57.9 mg); mp 230–232 °C.
1H NMR (400 MHz, CDCl3): δ = 8.71 (d, J = 8.0 Hz, 1 H), 8.41 (d, J = 8.0 Hz, 1 H), 8.33–8.27 (m, 2 H), 8.22 (d, J = 8.4 Hz, 1 H), 7.98 (s, 1 H), 7.73 (t, J = 7.2 Hz, 1 H), 7.66 (dd, J = 11.6, 7.2 Hz, 2 H), 7.50 (t, J = 7.6 Hz, 1 H).
13C NMR (100 MHz, CDCl3): δ = 149.2, 144.0, 133.7, 131.2, 130.8, 129.7, 129.5, 128.9, 128.3, 126.5, 126.3, 125.2, 124.5, 122.9, 122.4, 121.8, 121.1, 115.7, 115.2.
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11,12-Dichloro-2-methylbenzo[4,5]imidazo[1,2-f]phenanthridine (2b)[19]
Rf = 0.50 (hexane/EtOAc 4:1); white solid; yield: 94% (70 mg); mp 235–236 °C.
1H NMR (400 MHz, CDCl3): δ = 8.74 (d, J = 8.0 Hz, 1 H), 8.34 (s, 1 H), 8.32 (s, 1 H), 8.30 (s, 1 H), 8.05 (s, 1 H), 8.03 (s, 1 H), 7.77–7.69 (m, 1 H), 7.64 (t, J = 7.6 Hz, 1 H), 7.33 (d, J = 8.0 Hz, 1 H), 2.63 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 149.5, 144.1, 140.2, 133.9, 131.2, 130.9, 129.9, 128.5, 128.3, 126.4, 126.3 (× 2), 124.4, 122.6, 122.2, 121.1, 119.4, 116.0, 115.3, 22.2.
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11,12-Dichloro-2-ethylbenzo[4,5]imidazo[1,2-f]phenanthridine (2c)[19]
Rf = 0.60 (hexane/EtOAc 4:1); white solid; yield: 92% (54.9 mg); mp 240–242 °C.
1H NMR (700 MHz, CDCl3): δ = 8.64 (d, J = 8.0 Hz, 1 H), 8.24 (d, J = 8.0 Hz, 1 H), 8.22 (d, J = 8.0 Hz, 1 H), 8.20 (s, 1 H), 7.94 (s, 1 H), 7.93 (s, 1 H), 7.69 (t, J = 7.6 Hz, 1 H), 7.59 (t, J = 7.6 Hz, 1 H), 7.30 (d, J = 8.0 Hz, 1 H), 2.87 (q, J = 7.6 Hz, 2 H), 1.40 (t, J = 7.6 Hz, 3 H).
13C NMR (175 MHz, CDCl3): δ = 149.2, 146.3, 143.9, 133.7, 131.1, 130.7, 129.8, 128.4, 128.2, 126.3, 126.2, 125.0, 124.4, 122.3, 122.2, 120.9, 119.4, 115.2, 114.7, 29.2, 15.6.
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2-(tert-Butyl)-11,12-dichlorobenzo[4,5]imidazo[1,2-f]phenanthridine (2d)[19]
Rf = 0.60 (hexane/EtOAc 4:1); white solid; yield: 90% (53.6 mg); mp 233–234 °C.
1H NMR (400 MHz, CDCl3): δ = 8.66 (d, J = 8.0 Hz, 1 H), 8.31 (d, J = 8.4 Hz, 1 H), 8.27 (s, 1 H), 8.25 (s, 2 H), 7.95 (s, 1 H), 7.67 (t, J = 7.6 Hz, 1 H), 7.58 (d, J = 7.6 Hz, 1 H), 7.53 (d, J = 8.4 Hz, 1 H), 1.46 (s, 9 H).
13C NMR (100 MHz, CDCl3): δ = 153.4, 149.5, 144.2, 133.7, 131.2, 130.9, 129.9, 128.5, 128.2, 126.4, 126.3, 124.3, 122.9, 122.7, 122.3, 121.2, 119.3, 115.3, 112.5, 35.6, 31.5.
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11,12-Dichloro-2-fluorobenzo[4,5]imidazo[1,2-f]phenanthridine (2e)[19]
Rf = 0.60 (hexane/EtOAc 4:1); white solid; yield: 86% (51.3 mg); mp 262–264 °C.
1H NMR (400 MHz, CDCl3 + TFA-D): δ = 8.83 (d, J = 8.0 Hz, 1 H), 8.75 (dd, J = 9.2, 5.6 Hz, 1 H), 8.63 (s, 1 H), 8.58 (d, J = 8.4 Hz, 1 H), 8.31 (dd, J = 9.2, 2.0 Hz, 1 H), 8.24 (s, 1 H), 8.12 (t, J = 7.6 Hz, 1 H), 7.96 (t, J = 7.6 Hz, 1 H), 7.67–7.59 (m, 1 H).
13C NMR (100 MHz, CDCl3 + TFA-D): δ = 163.7 (d, J = 255.2 Hz), 145.2, 135.9, 134.2, 132.0, 131.9 (d, J = 10.5 Hz), 131.6, 131.3, 130.9, 127.8 (d, J = 4.1 Hz), 127.7, 126.9, 123.3, 119.2 (d, J = 2.9 Hz), 117.2, 116.9 (d, J = 22.2 Hz), 116.6, 115.3, 104.8 (d, J = 27.6 Hz).
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11,12-Dichloro-2-(trifluoromethyl)benzo[4,5]imidazo[1,2-f]phenanthridine (2f)[19]
Rf = 0.70 (hexane/EtOAc 4:1); white solid; yield: 83% (49.6 mg); mp 274–275 °C.
1H NMR (700 MHz, CDCl3): δ = 8.77 (d, J = 7.8 Hz, 1 H), 8.58 (d, J = 8.4 Hz, 1 H), 8.51 (s, 1 H), 8.39 (d, J = 8.1 Hz, 1 H), 8.28 (s, 1 H), 8.03 (s, 1 H), 7.82 (d, J = 7.4 Hz, 1 H), 7.79 (d, J = 8.6 Hz, 1 H), 7.75 (t, J = 7.5 Hz, 1 H).
13C NMR (175 MHz, CDCl3): δ = 148.9, 144.1, 133.6, 131.6, 131.2 (q, J = 32.8 Hz), 130.3, 129.0, 128.6, 127.4, 126.6 (q, J = 272 Hz)., 125.4, 124.9, 124.6, 123.6, 123.0, 121.7 (q, J = 3.2 Hz)., 121.6, 114.9, 112.8 (q, J = 3.6 Hz).
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11,12-Dichloro-7-fluorobenzo[4,5]imidazo[1,2-f]phenanthridine (2g)[19]
Rf = 0.65 (hexane/EtOAc 4:1); white solid; yield: 96% (57.3 mg); mp 278–280 °C.
1H NMR (400 MHz, CDCl3 + TFA-D): δ = 8.56 (d, J = 5.2 Hz, 2 H), 8.53 (s, 1 H), 8.46 (d, J = 8.4 Hz, 1 H), 8.40 (dd, J = 8.0, 2.4 Hz, 1 H), 8.10 (s, 1 H), 7.91 (t, J = 7.6 Hz, 1 H), 7.80 (t, J = 7.6 Hz, 1 H), 7.76–7.68 (m, 1 H).
13C NMR (100 MHz, CDCl3 + TFA-D): δ = 162.9 (d, J = 255.2 Hz), 143.9 (d, J = 3.5 Hz), 133.4, 132.7, 131.5, 131.2, 130.7, 128.5, 127.9, 127.8 (d, J = 2.3 Hz), 126.2 (d, J = 8.7 Hz), 125.0, 123.8 (d, J = 23.3 Hz), 121.7, 117.7 (d, J = 9.6 Hz), 117.4, 116.9, 116.8, 112.3 (d, J = 24.9 Hz).
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Benzo[4,5]imidazo[1,2-f]phenanthridine (2h)[19]
Rf = 0.40 (hexane/EtOAc 9:1); white solid; yield: 94% (56 mg); mp 145–146 °C.
1H NMR (700 MHz, CDCl3): δ = 8.84 (d, J = 8.0 Hz, 1 H), 8.48 (d, J = 8.4 Hz, 1 H), 8.39 (d, J = 8.0 Hz, 1 H), 8.30 (d, J = 8.0 Hz, 1 H), 8.28 (s, 1 H), 8.05 (d, J = 7.6 Hz, 1 H), 7.69 (t, J = 7.2 Hz, 1 H), 7.66–7.61 (m, 2 H), 7.51 (t, J = 7.6 Hz, 1 H), 7.48–7.43 (m, 2 H).
13C NMR (175 MHz, CDCl3): δ = 147.6, 144.4, 134.4, 131.9, 130.6, 129.6, 129.3, 128.7, 126.2, 124.6, 124.3 (× 2), 123.4, 123.1, 122.4, 121.8, 120.5, 116.1, 114.1.
#
2-Fluorobenzo[4,5]imidazo[1,2-f]phenanthridine (2i)[19]
Rf = 0.55 (hexane/EtOAc 4:1); white solid; yield: 91% (54.2 mg); mp 188–190 °C.
1H NMR (400 MHz, CDCl3): δ = 8.79 (d, J = 8.0 Hz, 1 H), 8.37 (dd, J = 8.8, 6.2 Hz, 1 H), 8.21 (t, J = 8.4 Hz, 2 H), 8.18–8.13 (m, 1 H), 8.03 (d, J = 8.0 Hz, 1 H), 7.69 (t, J = 7.6 Hz, 1 H), 7.63 (t, J = 7.6 Hz, 1 H), 7.53 (t, J = 7.6 Hz, 1 H), 7.50–7.45 (m, 1 H), 7.19 (dd, J = 11.6, 4.4 Hz, 1 H).
13C NMR (100 MHz, CDCl3): δ = 162.9 (d, J = 248.7 Hz), 147.7, 144.6, 135.3 (d, J = 10.6 Hz), 131.7, 130.8, 129.1, 128.6, 126.2, 126.1, 124.6, 123.4, 122.9, 122.2, 120.6, 118.2 (d, J = 2.9 Hz), 113.6, 112.2 (d, J = 22.1 Hz), 103.4 (d, J = 27.0 Hz).
#
1-(Benzo[4,5]imidazo[1,2-f]phenanthridin-2-yl)ethan-1-one (2j)[20]
Rf = 0.70 (hexane/EtOAc 7:3); white solid; yield: 88% (52.5 mg); mp 220–222 °C.
1H NMR (700 MHz, CDCl3): δ = 9.08 (s, 1 H), 8.87–8.80 (m, 1 H), 8.44 (d, J = 8.4 Hz, 1 H), 8.36 (d, J = 7.7 Hz, 1 H), 8.32 (d, J = 7.7 Hz, 1 H), 8.04 (d, J = 7.7 Hz, 1 H), 7.95 (d, J = 7.7 Hz, 1 H), 7.80–7.67 (m, 2 H), 7.57–7.48 (m, 2 H), 2.76 (s, 3 H).
13C NMR (175 MHz, CDCl3): δ = 196.8, 147.4, 144.6, 136.9, 134.5, 131.9, 130.8, 129.9, 128.6, 126.3, 125.7, 124.7, 124.5, 124.4, 124.2, 123.8, 123.2, 120.7, 115.7, 114.1, 26.9.
#
2-Methoxybenzo[4,5]imidazo[1,2-f]phenanthridine (2k)[19]
Rf = 0.60 (hexane/EtOAc 4:1); white solid; yield: 82% (49 mg); mp 219–221 °C.
1H NMR (400 MHz, CDCl3): δ = 8.69 (d, J = 7.6 Hz, 1 H), 8.08–8.01 (m, 2 H), 8.01–7.95 (m, 2 H), 7.68 (d, J = 1.2 Hz, 1 H), 7.59–7.49 (m, 2 H), 7.46 (t, J = 8.0 Hz, 1 H), 7.36 (t, J = 7.6 Hz, 1 H), 6.76 (dd, J = 8.8, 1.6 Hz, 1 H), 3.83 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 160.2, 147.8, 144.5, 135.2, 131.7, 130.3, 129.6, 127.4, 125.9, 125.2, 124.1, 122.8, 122.1, 121.6, 120.3, 114.8, 113.7, 110.6, 101.1, 55.6.
#
4-Methylbenzo[4,5]imidazo[1,2-f]phenanthridine (2l)
Rf = 0.50 (hexane/EtOAc 4:1); white solid; yield: 86% (68 mg); mp 148–150 °C.
1H NMR (700 MHz, CDCl3): δ = 8.56 (d, J = 7.7 Hz, 1 H), 7.57–7.51 (m, 2 H), 7.44 (t, J = 7.7 Hz, 2 H), 7.38 (d, J = 7.0 Hz, 1 H), 7.36–7.27 (m, 3 H), 7.19 (dd, J = 5.6, 2.8 Hz, 2 H), 1.95 (s, 3 H).
13C NMR (175 MHz, CDCl3): δ = 151.3, 140.6, 139.6, 137.1, 131.3, 130.9, 130.5, 130.5, 129.8, 129.2, 128.6, 128.2, 128.1, 127.2, 125.9, 123.3, 121.1, 121.0, 114.6, 20.2.
IR (KBr): 3048, 2883, 1452, 1368, 1220, 964, 764 cm–1.
HRMS (ESI-TOF): m/z calcd for C20H15N2 [M + H]+: 283.1235; found: 283.1208.
#
11,12-Dimethylbenzo[4,5]imidazo[1,2-f]phenanthridine (2m)[19]
Rf = 0.60 (hexane/EtOAc 4:1); white solid; yield: 95% (56.6 mg); mp 160–161 °C.
1H NMR (400 MHz, CDCl3): δ = 8.83 (d, J = 7.7 Hz, 1 H), 8.52 (d, J = 8.3 Hz, 1 H), 8.46 (d, J = 8.0 Hz, 1 H), 8.36 (d, J = 7.8 Hz, 1 H), 8.07 (s, 1 H), 7.78 (s, 1 H), 7.74–7.59 (m, 3 H), 7.48 (t, J = 7.6 Hz, 1 H), 2.53 (s, 3 H), 2.46 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 147.0, 143.3, 134.7, 133.3, 132.2, 130.5, 130.2, 129.4, 129.2, 128.7, 126.0, 124.3, 123.9 (× 2), 122.4, 121.8, 120.5, 116.1, 114.3, 21.2, 20.6.
#
2-(tert-Butyl)-11,12-dimethylbenzo[4,5]imidazo[1,2-f]phenanthridine (2n)[19]
Rf = 0.65 (hexane/EtOAc 4:1); white solid; yield: 87% (52 mg); mp 206–208 °C.
1H NMR (400 MHz, CDCl3): δ = 8.85 (d, J = 7.6 Hz, 1 H), 8.56 (s, 1 H), 8.39 (d, J = 8.4 Hz, 1 H), 8.34 (d, J = 7.6 Hz, 1 H), 8.07 (s, 1 H), 7.81 (s, 1 H), 7.67 (dd, J = 16.0, 7.2 Hz, 2 H), 7.56 (d, J = 8.0 Hz, 1 H), 2.54 (s, 3 H), 2.46 (s, 3 H), 1.54 (s, 9 H).
13C NMR (100 MHz, CDCl3): δ = 152.9, 146.9, 142.7, 134.4, 133.4, 132.2, 130.3, 130.3, 129.6, 128.3, 126.1, 124.0, 123.1, 122.2, 122.1, 120.2, 119.2, 114.4, 112.9, 35.5, 31.5, 21.5, 20.6.
#
2-Fluoro-11,12-dimethylbenzo[4,5]imidazo[1,2-f]phenanthridine (2o)[19]
Rf = 0.60 (hexane/EtOAc 4:1); white solid; yield: 83% (50 mg); mp 207–209 °C.
1H NMR (700 MHz, CDCl3): δ = 8.72 (d, J = 7.7 Hz, 1 H), 8.29 (dd, J = 8.4, 6.3 Hz, 1 H), 8.16 (d, J = 7.7 Hz, 1 H), 8.02 (dd, J = 10.5, 2.1 Hz, 1 H), 7.81 (s, 1 H), 7.69 (s, 1 H), 7.64 (t, J = 7.7 Hz, 1 H), 7.59 (t, J = 7.7 Hz, 1 H), 7.14–7.08 (m, 1 H), 2.48 (s, 3 H), 2.42 (s, 3 H).
13C NMR (175 MHz, CDCl3): δ = 162.8 (d, J = 248.2 Hz), 146.8, 143.0, 135.3 (d, J = 10.9 Hz), 133.6, 132.5, 130.3, 130.0, 128.8, 128.4, 125.9, 125.9 (d, J = 9.8 Hz), 122.9, 122.0, 120.4, 118.0 (d, J = 2.4 Hz), 113.8, 111.7 (d, J = 22.0 Hz), 103.1 (d, J = 26.9 Hz), 21.1, 20.5.
#
11,12-Dimethyl-2-(trifluoromethyl)benzo[4,5]imidazo[1,2-f]phenanthridine (2p)[19]
Rf = 0.60 (hexane/EtOAc 4:1); white solid; yield: 81% (48.4 mg); mp 252–253 °C.
1H NMR (400 MHz, CDCl3): δ = 8.72 (d, J = 7.2 Hz, 1 H), 8.59 (s, 1 H), 8.43 (d, J = 8.4 Hz, 1 H), 8.26 (d, J = 7.6 Hz, 1 H), 7.83 (s, 1 H), 7.71 (s, 1 H), 7.70 – 7.62 (m, 3 H), 2.50 (s, 3 H), 2.42 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 145.9, 141.6, 134.5, 133.8, 133.4, 130.9, 130.8 (q, J = 33.0 Hz), 129.9, 129.7, 128.2, 126.3, 124.9, 124.5, 123.9 (q, J = 272.5 Hz), 123.3, 122.8, 120.9 (q, J = 3.3 Hz), 120.2, 113.9, 113.1 (q, J = 4.2 Hz), 21.3, 20.5.
#
3-Chloro-11,12-dimethylbenzo[4,5]imidazo[1,2-f]phenanthridine (2q)[19]
Rf = 0.65 (hexane/EtOAc 4:1); white solid; yield: 85% (51 mg); mp 208–210 °C.
1H NMR (400 MHz, CDCl3): δ = 8.83–8.77 (m, 1 H), 8.41 (s, 1 H), 8.40–8.36 (m, 1 H), 8.27 (d, J = 8.0 Hz, 1 H), 7.96 (s, 1 H), 7.76 (s, 1 H), 7.73–7.64 (m, 2 H), 7.60 (dd, J = 8.8, 2.0 Hz, 1 H), 2.52 (s, 3 H), 2.46 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 146.7, 143.3, 133.6, 133.1, 132.5, 130.3, 130.3, 129.9, 129.4, 128.9, 128.3, 126.1, 124.1, 124.1, 123.4, 122.5, 120.6, 117.3, 114.0, 21.2, 20.6.
#
2-Methoxy-11,12-dimethylbenzo[4,5]imidazo[1,2-f]phenanthridine (2r)[19]
Rf = 0.40 (hexane/EtOAc 4:1); white solid; yield: 81% (48.3 mg); mp 180–182 °C.
1H NMR (400 MHz, CDCl3): δ = 8.78 (d, J = 8.0 Hz, 1 H), 8.30 (d, J = 8.8 Hz, 1 H), 8.21 (d, J = 8.0 Hz, 1 H), 7.96 (s, 1 H), 7.93 (s, 1 H), 7.76 (s, 1 H), 7.65 (t, J = 7.6 Hz, 1 H), 7.58 (t, J = 7.6 Hz, 1 H), 7.00 (d, J = 8.0 Hz, 1 H), 3.99 (s, 3 H), 2.50 (s, 3 H), 2.45 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 160.4, 147.3, 143.3, 135.7, 133.3, 132.0, 130.4, 130.2, 129.6, 127.6, 125.9, 125.5, 122.6, 121.7, 120.4, 115.2, 114.1, 110.3, 101.7, 55.8, 21.2, 20.5.
#
1-(11,12-Dimethylbenzo[4,5]imidazo[1,2-f]phenanthridin-2-yl)ethan-1-one (2s)[20]
Rf = 0.70 (hexane/EtOAc 7:3); white solid; yield: 84% (50 mg); mp 197–199 °C.
1H NMR (400 MHz, CDCl3): δ = 8.23 (dd, J = 5.6, 3.6 Hz, 1 H), 8.01 (s, 1 H), 7.99 (s, 1 H), 7.54 (dd, J = 5.6, 3.6 Hz, 2 H), 7.45 (s, 1 H), 7.44–7.38 (m, 2 H), 7.26 (s, 1 H), 2.62 (s, 3 H), 2.45 (s, 3 H), 2.41 (s, 3 H).
#
11,12-Difluorobenzo[4,5]imidazo[1,2-f]phenanthridine (2t)[19]
Rf = 0.60 (hexane/EtOAc 4:1); white solid; yield: 91% (90 mg); mp 239–240 °C.
1H NMR (400 MHz, CDCl3): δ = 8.68 (d, J = 7.6 Hz, 1 H), 8.37 (d, J = 8.0 Hz, 1 H), 8.27 (d, J = 8.0 Hz, 1 H), 8.16 (d, J = 8.4 Hz, 1 H), 7.99 (dd, J = 10.8, 7.0 Hz, 1 H), 7.75–7.66 (m, 2 H), 7.62 (dd, J = 14.0, 7.2 Hz, 2 H), 7.46 (t, J = 7.6 Hz, 1 H).
13C NMR (100 MHz, CDCl3): δ = 148.8 (d, J = 14.8 Hz), 148.7 (d, J = 242.5 Hz), 148.5 (d, J = 242.5 Hz), 146.4 (d, J = 14.4 Hz), 140.4 (d, J = 11.2 Hz), 133.7, 130.8, 129.4, 129.3, 128.9, 126.7 (d, J = 10.5 Hz), 125.9, 124.7 (d, J = 52.3 Hz), 123.1, 122.4, 121.7, 115.3, 107.3 (d, J = 19.2 Hz), 102.3 (d, J = 24.7 Hz).
#
2-Ethyl-11,12-difluorobenzo[4,5]imidazo[1,2-f]phenanthridine (2u)[19]
Rf = 0.60 (hexane/EtOAc 4:1); white solid; yield: 93% (64.7 mg); mp 250–251 °C.
1H NMR (400 MHz, CDCl3): δ = 8.74 (d, J = 7.6 Hz, 1 H), 8.35 (d, J = 8.4 Hz, 1 H), 8.32 (d, J = 8.0 Hz, 1 H), 8.10 (d, J = 11.2 Hz, 2 H), 7.73 (dd, J = 17.2, 9.2 Hz, 2 H), 7.64 (t, J = 7.2 Hz, 1 H), 7.36 (d, J = 8.0 Hz, 1 H), 2.92 (dd, J = 14.8, 7.2 Hz, 2 H), 1.42 (t, J = 7.6 Hz, 3 H).
13C NMR (100 MHz, CDCl3): δ = 149.3 (d, J = 2.5 Hz), 148.8 (d, J = 14.9 Hz), 148.7 (d, J = 243.3 Hz), 148.5 (d, J = 243.1 Hz), 146.3, 140.5 (d, J = 9.7 Hz), 133.9, 130.8, 129.7, 128.5, 126.8 (d, J = 10.5 Hz), 125.9, 125.0, 124.5, 122.8, 122.3, 119.6, 114.6, 107.3 (d, J = 19.2 Hz), 102.5 (d, J = 24.5 Hz), 29.3, 15.7.
#
2-Bromobenzo[4,5]imidazo[1,2-f]phenanthridine (2v)
Rf = 0.50 (hexane/EtOAc 4:1); white solid; yield: 96%; mp 214–216 °C.
1H NMR (400 MHz, CDCl3): δ = 8.72 (s, 1 H), 8.48 (s, 1 H), 8.11 (s, 3 H), 7.99 (d, J = 6.2 Hz, 1 H), 7.61 (s, 2 H), 7.54–7.36 (m, 3 H).
13C NMR (100 MHz, CDCl3): δ = 147.2, 144.2, 134.9, 131.4, 130.7, 129.0, 128.7, 127.8, 127.5, 126.2, 125.4, 124.6, 123.4, 123.1, 122.9, 122.1, 120.5, 118.9, 113.7.
IR (KBr): 3054, 2920, 1533, 1446, 1085, 815, 724 cm–1.
HRMS (ESI-TOF): m/z calcd for C19H12 79BrN2 [M + H]+: 347.0184; found: 347.0215; C19H12 81BrN2 [M + H]+: 349.0184; found: 349.0200.
#
Mixture of 11-Nitrobenzo[4,5]imidazo[1,2-f]phenanthridine and 12-Nitrobenzo[4,5]imidazo[1,2-f]phenanthridine (2a′)[19]
Rf = 0.55 (hexane/EtOAc 4:1); inseparable pale yellow solid (10:3); yield: 89% (53 mg); mp 254–256 °C.
1H NMR (400 MHz, CDCl3): δ = 9.27 (s, 1 H), 8.84 (d, J = 7.1 Hz, 1.3 H), 8.52 (d, J = 8.1 Hz, 2.3 H), 8.47–8.30 (m, 3.2 H), 8.01 (d, J = 8.9 Hz, 1.3 H), 7.80 (dd, J = 14.5, 7.9 Hz, 2.3 H), 7.73 (t, J = 7.2 Hz, 1.6 H), 7.61 (t, J = 7.2 Hz, 1.3 H).
13C NMR (100 MHz, CDCl3): δ = 151.8, 149.2, 142.9, 133.6, 131.9, 131.7, 130.9, 130.3, 130.1, 129.9, 129.7, 129.2, 126.7, 125.8, 124.7, 122.7, 122.6, 122.0, 120.2, 120.0, 118.1, 116.5, 116.2, 113.8, 110.9.
#
Mixture of 2-Ethyl-11-nitrobenzo[4,5]imidazo[1,2-f]phenanthridine and 2-Ethyl-12-nitrobenzo[4,5]imidazo[1,2-f]phenanthridine (2b′)[20]
Rf = 0.50 (hexane/EtOAc 4:1); inseparable pale yellow solid (2:1); yield: 92% (64 mg); mp 241–243 °C.
1H NMR (400 MHz, CDCl3): δ = 8.94 (s, 1 H), 8.59 (dd, J = 18.0, 8.3 Hz, 2 H), 8.27 (d, J = 8.4 Hz, 1 H), 8.15 (dd, J = 13.8, 7.6 Hz, 3.5 H), 8.02 (d, J = 9.1 Hz, 0.5 H), 7.96 (d, J = 9.7 Hz, 0.5 H), 7.81 (d, J = 8.9 Hz, 1 H), 7.74–7.64 (m, 1.5 H), 7.63–7.51 (m, 1.5 H), 7.27 (d, J = 10.7 Hz, 1.5 H), 2.91–2.80 (m, 3 H), 1.41 (t, J = 7.5 Hz, 4.5 H).
#
Mixture of 11-Methylbenzo[4,5]imidazo[1,2-f]phenanthridine and 12-Methylbenzo[4,5]imidazo[1,2-f]phenanthridine (2c′)[19]
Rf = 0.60 (hexane/EtOAc 7:3); inseparable white solid (5:2); yield: 94% (93.3 mg); mp 161–163 °C.
1H NMR (400 MHz, CDCl3 + TFA-D): δ = 9.06 (d, J = 16.4 Hz, 1 H), 8.89–8.78 (m, 1.4 H), 8.78–8.70 (m, 2.8 H), 8.69–8.61 (m, 1.4 H), 8.40 (d, J = 14.4 Hz, 0.4 H), 8.11 (dd, J = 16.8, 8.6 Hz, 1.4 H), 8.03 (d, J = 8.9 Hz, 1.4 H), 8.01–7.94 (m, 2.4 H), 7.90 (d, J = 8.3 Hz, 1.4 H), 7.68–7.61 (m, 0.4 H), 2.76–2.68 (m, 4.2 H).
#
Mixture of 2,11-Dimethylbenzo[4,5]imidazo[1,2-f]phenanthridine and 2,12-Dimethylbenzo[4,5]imidazo[1,2-f]phenanthridine (2d′)[19]
Rf = 0.45 (hexane/EtOAc 4:1); inseparable white solid (2:1); yield: 96% (57.2 mg); mp 185–187 °C.
1H NMR (400 MHz, CDCl3): δ = 8.78 (s, 0.5 H), 8.76 (s, 1 H), 8.24–8.10 (m, 4.5 H), 8.07 (d, J = 5.2 Hz, 1 H), 7.98 (s, 0.5 H), 7.88 (d, J = 8.2 Hz, 0.5 H), 7.77 (s, 1 H), 7.68–7.52 (m, 3 H), 7.30 (d, J = 8.1 Hz, 0.5 H), 7.21 (d, J = 8.4 Hz, 1 H), 7.16 (s, 1.5 H), 2.63 (s, 1.5 H), 2.56 (s, 3 H), 2.52 (s, 4.5 H).
13C NMR (100 MHz, CDCl3): δ = 147.7, 147.4, 144.9, 142.7, 139.5, 134.6, 134.5, 134.4, 133.9, 132.7, 132.1, 130.2, 130.2, 129.9, 129.6, 129.5, 128.1, 125.9, 125.9, 125.7, 125.4, 124.3, 123.9, 123.2, 123.1, 122.0, 120.1, 119.8, 119.2, 119.1, 116.2, 116.2, 114.1, 113.5, 22.5, 22.1, 22.0, 21.7.
#
Mixture of 2-Ethyl-11-methylbenzo[4,5]imidazo[1,2-f]phenanthridine and 2-Ethyl-12-methylbenzo[4,5]imidazo[1,2-f]phenanthridine (2e′)[19]
Rf = 0.60 (hexane/EtOAc 4:1); inseparable white solid (2:1); yield: 93% (55.4 mg); mp 274–176 °C.
1H NMR (400 MHz, CDCl3): δ = 8.75 (d, J = 7.2 Hz, 1.5 H), 8.22–8.11 (m, 4.5 H), 8.05 (d, J = 8.4 Hz, 1 H), 7.96 (s, 0.5 H), 7.87 (d, J = 8.0 Hz, 0.5 H), 7.76 (s, 1 H), 7.58 (dd, J = 16.8, 8.0 Hz, 3 H), 7.29 (d, J = 8.4 Hz, 0.5 H), 7.19 (t, J = 8.0 Hz, 2 H), 2.81 (dd, J = 14.0, 7.2 Hz, 3 H), 2.62 (s, 1.5 H), 2.55 (s, 3 H), 1.36 (t, J = 7.6 Hz, 4.5 H).
#
11-Bromo-2-ethylbenzo[4,5]imidazo[1,2-f]phenanthridine or 12-Bromo-2-ethylbenzo[4,5]imidazo[1,2-f]phenanthridine (2f′)[19]
Rf = 0.70 (hexane/EtOAc 4:1); white solid; yield: 90% (54 mg); mp 194–196 °C.
1H NMR (400 MHz, CDCl3): δ = 8.72 (d, J = 8.0 Hz, 1 H), 8.25 (t, J = 8.0 Hz, 2 H), 8.11 (s, 1 H), 8.09 (d, J = 1.6 Hz, 1 H), 8.06 (d, J = 8.8 Hz, 1 H), 7.68 (t, J = 7.6 Hz, 1 H), 7.60 (t, J = 7.6 Hz, 1 H), 7.49 (dd, J = 8.8, 1.6 Hz, 1 H), 7.29 (d, J = 8.0 Hz, 1 H), 2.87 (q, J = 7.6 Hz, 2 H), 1.39 (t, J = 7.6 Hz, 3 H).
13C NMR (100 MHz, CDCl3): δ = 148.6, 146.1, 145.9, 134.1, 130.8, 130.8, 129.9, 128.3, 126.2, 125.6, 124.8, 124.3, 123.1, 122.7, 122.1, 119.5, 117.2, 115.0, 114.9, 29.2, 15.6.
#
11-Bromo-2-fluorobenzo[4,5]imidazo[1,2-f]phenanthridine or 12-Bromo-2-fluorobenzo[4,5]imidazo[1,2-f]phenanthridine (2g′)[19]
Rf = 0.60 (hexane/EtOAc 4:1); white solid; yield: 88% (52.6 mg); mp 234–236 °C.
1H NMR (400 MHz, CDCl3): δ = 8.80 (s, 1 H), 8.46 (s, 1 H), 8.31 (s, 1 H), 8.14 (s, 3 H), 7.77 (s, 1 H), 7.69 (s, 1 H), 7.57 (s, 1 H), 7.26 (s, 1 H).
#
11-Bromo-2-methylbenzo[4,5]imidazo[1,2-f]phenanthridine or 12-Bromo-2-methylbenzo[4,5]imidazo[1,2-f]phenanthridine (2h′)[19]
Rf = 0.55 (hexane/EtOAc 4:1); white solid; yield: 91% (54.3 mg); mp 200–201 °C.
1H NMR (400 MHz, CDCl3): δ = 8.73 (d, J = 8.0 Hz, 1 H), 8.25 (d, J = 4.8 Hz, 1 H), 8.23 (d, J = 5.2 Hz, 1 H), 8.08 (d, J = 5.2 Hz, 2 H), 8.05 (s, 1 H), 7.69 (t, J = 7.6 Hz, 1 H), 7.61 (t, J = 7.6 Hz, 1 H), 7.48 (d, J = 8.8 Hz, 1 H), 7.24 (s, 1 H), 2.56 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 148.6, 145.9, 139.9, 134.0, 130.8, 129.8, 128.3, 126.2, 126.0, 125.6, 124.6, 124.2, 123.1, 122.7, 122.1, 119.3, 117.2, 116.1, 115.1, 22.1.
#
11-Chloro-2-methylbenzo[4,5]imidazo[1,2-f]phenanthridine and 12-Chloro-2-methylbenzo[4,5]imidazo[1,2-f]phenanthridine (2i′)[19]
Rf = 0.40 (hexane/EtOAc 9:1); white solid; yield: 93% (55.4 mg); mp 222–223 °C.
1H NMR (400 MHz, CDCl3): δ = 8.75 (d, J = 7.6 Hz, 1 H), 8.21 (t, J = 7.6 Hz, 2 H), 8.08 (d, J = 8.8 Hz, 1 H), 8.04 (s, 1 H), 7.93 (s, 1 H), 7.69 (t, J = 7.6 Hz, 1 H), 7.61 (t, J = 7.6 Hz, 1 H), 7.35 (d, J = 8.4 Hz, 1 H), 7.23 (d, J = 8.0 Hz, 1 H), 2.54 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 148.4, 144.7, 142.2, 139.9, 133.8, 131.0, 130.2, 129.9, 129.8, 128.4, 126.3, 126.2, 124.2, 123.2, 122.1, 119.7, 119.2, 116.1, 114.7, 22.1.
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2-(tert-Butyl)-11-chlorobenzo[4,5]imidazo[1,2-f]phenanthridine or 2-(tert-Butyl)-12-chlorobenzo[4,5]imidazo[1,2-f]phenanthridine (2j′)[19]
Rf = 0.60 (hexane/EtOAc 4:1); white solid; yield: 91% (54.3 mg); mp 199–200 °C.
1H NMR (400 MHz, CDCl3): δ = 8.77 (d, J = 8.0 Hz, 1 H), 8.44 (s, 1 H), 8.38 (d, J = 8.4 Hz, 1 H), 8.32 (d, J = 8.0 Hz, 1 H), 8.16 (d, J = 8.8 Hz, 1 H), 7.96 (d, J = 1.6 Hz, 1 H), 7.71 (t, J = 7.6 Hz, 1 H), 7.62 (t, J = 7.6 Hz, 1 H), 7.57 (d, J = 8.4 Hz, 1 H), 7.40 (dd, J = 8.8, 1.6 Hz, 1 H), 1.53 (s, 9 H).
13C NMR (100 MHz, CDCl3): δ = 153.2, 148.9, 145.7, 134.1, 130.8, 130.5, 129.8, 129.7, 128.4, 126.2, 124.2, 123.1, 122.9, 122.6, 122.2, 120.1, 119.3, 114.5, 112.7, 35.5, 31.6.
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11-Chloro-2-fluorobenzo[4,5]imidazo[1,2-f]phenanthridine or 12-chloro-2-fluorobenzo[4,5]imidazo[1,2-f]phenanthridine (2k′)[19]
Rf = 0.50 (hexane/EtOAc 4:1); white solid; yield: 86% (51.3 mg); mp 238–240 °C.
1H NMR (400 MHz, CDCl3): δ = 8.76 (d, J = 7.8 Hz, 1 H), 8.42 (dd, J = 8.9, 6.0 Hz, 1 H), 8.26 (d, J = 8.2 Hz, 1 H), 8.11–8.03 (m, 2 H), 7.98 (d, J = 1.5 Hz, 1 H), 7.75 (t, J = 7.5 Hz, 1 H), 7.67 (t, J = 7.5 Hz, 1 H), 7.42 (dd, J = 8.8, 1.6 Hz, 1 H), 7.23 (d, J = 2.2 Hz, 1 H).
13C NMR (100 MHz, CDCl3): δ = 162.9 (d, J = 249.7 Hz), 148.4, 144.7, 134.6 (d, J = 10.5 Hz), 131.4, 130.6, 129.9, 129.3, 128.9, 126.5, 126.4, 123.8, 122.3, 121.9, 119.9, 118.3 (d, J = 2.5 Hz), 114.3, 112.8 (d, J = 22.1 Hz), 103.4 (d, J = 27.0 Hz).
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2-Phenylbenzo[4,5]imidazo[1,2-f]phenanthridine (3)
Rf = 0.50 (hexane/EtOAc 4:1); white solid; yield: 91% (90 mg); mp 227–228 °C.
1H NMR (400 MHz, CDCl3): δ = 8.79 (d, J = 7.6 Hz, 1 H), 8.60 (s, 1 H), 8.34 (d, J = 8.4 Hz, 1 H), 8.25 (t, J = 7.6 Hz, 2 H), 8.03 (d, J = 8.0 Hz, 1 H), 7.71 (d, J = 7.6 Hz, 2 H), 7.68–7.57 (m, 3 H), 7.54 (t, J = 7.6 Hz, 2 H), 7.51–7.41 (m, 3 H).
13C NMR (100 MHz, CDCl3): δ = 147.6, 144.4, 142.1, 140.1, 134.8, 131.8, 130.6, 129.4, 129.3, 128.6, 128.3, 127.4, 126.2, 124.6, 124.3, 123.3, 123.2, 123.2, 122.3, 120.7, 120.5, 114.4, 114.0.
IR (KBr): 3047, 1607, 1445, 1417, 1350, 752, 726 cm–1.
HRMS (ESI-TOF): m/z calcd for C25H17N2 [M + H]+: 345.1392; found: 345.1425.
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(E)-2-Styrylbenzo[4,5]imidazo[1,2-f]phenanthridine (4)
Rf = 0.50 (hexane/EtOAc 4:1); white solid; yield: 93% (99 mg); mp 242–244 °C.
1H NMR (400 MHz, CDCl3): δ = 8.82 (d, J = 7.6 Hz, 1 H), 8.41 (s, 1 H), 8.26 (dd, J = 11.8, 8.1 Hz, 2 H), 8.20 (d, J = 7.9 Hz, 1 H), 8.07–8.00 (m, 1 H), 7.69–7.61 (m, 2 H), 7.60 (d, J = 7.4 Hz, 2 H), 7.55–7.52 (m, 1 H), 7.51–7.45 (m, 2 H), 7.43 (t, J = 7.6 Hz, 2 H), 7.34 (t, J = 7.3 Hz, 1 H), 7.23 (d, J = 16.4 Hz, 1 H), 7.17 (d, J = 16.3 Hz, 1 H).
13C NMR (100 MHz, CDCl3): δ = 147.4, 144.1, 138.5, 136.8, 134.7, 131.8, 130.9, 130.7, 129.5, 128.9, 128.8, 128.7, 128.4, 127.6, 127.0, 126.3, 124.5, 123.2, 122.9, 122.3, 122.2, 120.9, 120.4, 114.2, 114.1.
IR (KBr): 3021, 1604, 1446, 1357, 1258, 959, 723 cm–1.
HRMS (ESI-TOF): m/z calcd for C27H19N2 [M + H]+: 371.1548; found: 371.1545.
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Radical Trapping Experiments with TEMPO/BHT/Diphenylethylene
To an oven-dried round-bottomed flask, 2-([1,1′-biphenyl]-2-yl)-5,6-dichloro-1H-benzo[d]imidazole (1a; 60 mg, 0.176 mmol), NIS (80 mg, 0.356 mmol), and TEMPO (28 mg, 0.176 mmol) were taken in THF (1.5 mL) solvent. Then the reaction mixture was stirred at rt for 22 h. After completion of the reaction, no product formation took place. Similar experiments were performed using other radical trapping reagents such as BHT (39 mg, 0.176 mmol) and 1,1-diphenylethylene (64 mg, 0.353 mmol) under the standard reaction conditions. Unfortunately, in all these cases no desired product was formed.
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EPR Experiments
In a 10 mL round-bottomed flask, 2-([1,1′-biphenyl]-2-yl)-5,6-dichloro-1H-benzo[d]imidazole (1a; 60 mg, 0.176 mmol) and NIS (80 mg, 0.356 mmol) were dissolved in TFE (1.5 mL). After the addition of DMPO (20 μL), the reaction mixture was stirred at rt for 6 h and the EPR experiment was performed.
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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-2063-0221.
Control experiments, characterization data, and NMR spectra are included.
- Supporting Information
-
References
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- 20 Bera SK, Alam MT, Mal P. J. Org. Chem. 2019; 84: 12009
- 21 Bal A, Maiti S, Mal P. Chem. Asian J. 2020; 15: 624
- 22 Colomer I, Chamberlain AE. R, Haughey MB, Donohoe TJ. Nat. Rev. Chem. 2017; 1: 0088
- 23 Parida SK, Mandal T, Das S, Hota SK, De Sarkar S, Murarka S. ACS Catal. 2021; 11: 1640
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Corresponding Author
Publication History
Received: 14 February 2023
Accepted after revision: 27 March 2023
Accepted Manuscript online:
27 March 2023
Article published online:
20 April 2023
© 2024. Thieme. All rights reserved
Georg Thieme Verlag KG
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References
- 1 Colacino E, Porcheddu A, Charnay C, Delogu F. React. Chem. Eng. 2019; 4: 1179
- 2a Choudhuri K, Pramanik M, Mal P. J. Org. Chem. 2020; 85: 11997
- 2b Maertens G, Deruer E, Denis M, Canesi S. J. Org. Chem. 2020; 85: 6098
- 2c Bayeh L, Le PQ, Tambar UK. Nature 2017; 547: 196
- 2d Duchemin N, Aubert S, de Souza JV, Bethge L, Vonhoff S, Bronowska AK, Smietana M, Arseniyadis S. JACS Au 2022; 2: 1910
- 3a Dahiya A, Sahoo AK, Chakraborty N, Das B, Patel BK. Org. Biomol. Chem. 2022; 20: 2005
- 3b Singh FV, Wirth T. ARKIVOC 2021; (vii): : 12
- 3c Ghosh D, Ghosh S, Hajra A. Adv. Synth. Catal. 2021; 363: 5047
- 3d Borah B, Chowhan LR. RSC Adv. 2021; 11: 37325
- 3e Bagdi AK, Rahman M, Bhattacherjee D, Zyryanov GV, Ghosh S, Chupakhin ON, Hajra A. Green Chem. 2020; 22: 6632
- 3f Pal S, Chatterjee R, Santra S, Zyryanov GV, Majee A. Adv. Synth. Catal. 2021; 363: 5300
- 4 van der Helm MP, Klemm B, Eelkema R. Nat. Rev. Chem. 2019; 3: 491
- 5a Chan AY, Perry IB, Bissonnette NB, Buksh BF, Edwards GA, Frye LI, Garry OL, Lavagnino MN, Li BX, Liang Y, Mao E, Millet A, Oakley JV, Reed NL, Sakai HA, Seath CP, MacMillan DW. C. Chem. Rev. 2022; 122: 1485
- 5b De Vos D, Gadde K, Maes BU. W. Synthesis 2023; 55: 193
- 5c Vanderghinste J, Das S. Synthesis 2022; 54: 3383
- 6 Yi D, Bayer T, Badenhorst CP. S, Wu S, Doerr M, Höhne M, Bornscheuer UT. Chem. Soc. Rev. 2021; 50: 8003
- 7 Kerru N, Gummidi L, Maddila S, Gangu KK, Jonnalagadda SB. Molecules 2020; 25: 1909
- 8 Joule JA. Adv. Heterocycl. Chem. 2016; 119: 81
- 9 Maiti S, Alam MT, Bal A, Mal P. Adv. Synth. Catal. 2019; 361: 4401
- 10 Bariwal J, Van der Eycken E. Chem. Soc. Rev. 2013; 42: 9283
- 11 Ruiz-Castillo P, Buchwald SL. Chem. Rev. 2016; 116: 12564
- 12 Farhang M, Akbarzadeh AR, Rabbani M, Ghadiri AM. Polyhedron 2022; 227: 116124
- 13 Heravi MM, Kheilkordi Z, Zadsirjan V, Heydari M, Malmir M. J. Organomet. Chem. 2018; 861: 17
- 14 Li J, Zhang Y, Kuruvinashetti K, Kornienko N. Nat. Rev. Chem. 2022; 6: 303
- 15a O’Broin CQ, Fernández P, Martínez C, Muñiz K. Org. Lett. 2016; 18: 436
- 15b Cao H, Cheng Q, Studer A. Science 2022; 378: 779
- 15c Sosnicki JG, Borzyszkowska-Ledwig A, Idzik TJ, Lubowicz MM, Maciejewska G, Struk L. Org. Lett. 2022; 24: 8498
- 15d Sun L, Cui J, Nie S, Xie L, Wang Y, Wu L. Eur. J. Org. Chem. 2022; e202200505
- 15e Yang M, Hua J, Wang H, Ma T, Liu C, He W, Zhu N, Hu Y, Fang Z, Guo K. J. Org. Chem. 2022; 87: 8445
- 16 Horton DA, Bourne GT, Smythe ML. Chem. Rev. 2003; 103: 893
- 17a Yan L, Zhao D, Lan J, Cheng Y, Guo Q, Li X, Wu N, You J. Org. Biomol. Chem. 2013; 11: 7966
- 17b Chen Y.-H, Chen C.-H, Chang C.-M, Fan B.-A, Chen D.-G, Lee J.-H, Chiu T.-L, Chou P.-T, Leung M.-k. J. Mater. Chem. C 2020; 8: 3571
- 17c Gao Z, Liu Y, Wang Z, Shen F, Liu H, Sun G, Yao L, Lv Y, Lu P, Ma Y. Chem. Eur. J. 2013; 19: 2602
- 17d Ohsawa T, Sasabe H, Watanabe T, Nakao K, Komatsu R, Hayashi Y, Hayasaka Y, Kido J. Adv. Opt. Mater. 2019; 7: 1801282
- 18a Chen C, Shang G, Zhou J, Yu Y, Li B, Peng J. Org. Lett. 2014; 16: 1872
- 18b Zhao G, Chen C, Yue Y, Yu Y, Peng J. J. Org. Chem. 2015; 80: 2827
- 19 Bera SK, Boruah PJ, Parida SS, Paul AK, Mal P. J. Org. Chem. 2021; 86: 9587
- 20 Bera SK, Alam MT, Mal P. J. Org. Chem. 2019; 84: 12009
- 21 Bal A, Maiti S, Mal P. Chem. Asian J. 2020; 15: 624
- 22 Colomer I, Chamberlain AE. R, Haughey MB, Donohoe TJ. Nat. Rev. Chem. 2017; 1: 0088
- 23 Parida SK, Mandal T, Das S, Hota SK, De Sarkar S, Murarka S. ACS Catal. 2021; 11: 1640
- 24a Bera SK, Mal P. J. Org. Chem. 2021; 86: 14144
- 24b Bhanja R, Bera SK, Mal P. Chem. Commun. 2023; 59: 4455
- 24c Wang H, Li Y, Tang Z, Wang S, Zhang H, Cong H, Lei A. ACS Catal. 2018; 8: 10599
