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DOI: 10.1055/s-0036-1590962
Stereospecific Nickel-Catalyzed Borylation of Secondary Benzyl Pivalates
MINECO (CTQ2015-65496-R & Severo Ochoa Excellence Accreditation 2014-2018, SEV-2013-0319) and Cellex Foundation.
Publication History
Received: 01 August 2017
Accepted after revision: 26 October 2017
Publication Date:
08 November 2017 (online)
Published as part of the Cluster C–O Activation
Abstract
A stereoselective nickel-catalyzed direct borylation of enantioenriched secondary benzyl pivalates is described. This methodology is characterized by an intriguing cooperativity of simple nickel and copper salts to promote the targeted C–B bond formation under mild reaction conditions. Unlike classical SN2-type processes, this protocol occurs with a neat retention of configuration, resulting in synthetically versatile benzyl boronic esters with excellent stereochemical fidelity.
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In recent years, C–O electrophiles have received considerable attention as counterparts in a myriad of metal-catalyzed cross-coupling reactions.[1] Such interest primarily arises from the lack of toxicity and readily accessibility of alcohols, as well as the possibility of implementing orthogonal techniques in the presence of organic halide partners, thus becoming powerful synthetic alternatives for building up molecular complexity. Despite the wealth of literature data when forging C–C bonds,[1] the design of enantioselective cross-coupling reactions via functionalization of C–O electrophiles other than particularly activated organic sulfonates such as aryl triflates or tosylates is still in its infancy (Scheme [1], paths b vs a).[2]
Although the employment of chiral ligands has become routine in enantioselective C–C bond-forming reactions,[3] an attractive alternative in these endeavours consists of the implementation of stereospecific coupling reactions.[4] In these rather appealing scenarios, the reaction outcome is dictated by the stereochemistry of the starting precursor, thus avoiding the need for sophisticated, oftentimes expensive, ancillary chiral ligands. Illustrative examples are the elegant protocols described by Jarvo[5] or Watson[6] that make use of enantioenriched benzyl C–O electrophiles to promote a variety of stereospecific C–C bond-forming reactions with well-defined organometallic reagents, allowing to reliably transfer the stereochemical information in the starting precursors with high fidelity. Despite the advances realized, stereoselective C–O bond-cleavage reactions remain predominantly confined to C–C bond formations (Scheme [1], path b).[5] [6] In sharp contrast, the paucity of stereoselective C–heteroatom bond-forming reactions of C–O electrophiles other than particularly activated organic sulfonates is certainly striking,[7] a rather surprising observation if one takes into consideration the prevalence of C–heteroatom bonds in pharmaceuticals.[8] A remarkable step forward has recently been described by Tobisu and Chatani,[9] in which 2-pyridyl benzyl ethers can be used for such purposes via chelation control. However, the stereoselective C–heteroatom bond formation of benzyl esters still remains elusive. Prompted by our ongoing interest in C–O bond functionalization[10] and by the versatility of organoboranes as synthons in organic synthesis,[11] we wondered whether a stereospecific borylation of enantioenriched benzyl pivalates could be implemented (Scheme [2]). Herein, we present our investigations towards this goal, demonstrating the synergy of Ni and Cu catalysts for promoting a stereoretentive borylation event of benzyl pivalates under mild conditions, constituting the first example of a stereospecific C–heteroatom bond formation of readily accessible organic ester derivatives.
a Reaction conditions: 1a (0.20 mmol), B2nep2 (0.30 mmol), Ni(COD)2 (7.5 mol%), PCy3 (7.5 mol%), CuF2 (30 mol%), CsF (30 mol%) in PhMe, 50 °C.
b GC yields using decane as internal standard.
c Calculated by HPLC of the corresponding oxidized alcohol due to the inherent instability of 2a.
We began our study by evaluating the borylation reaction of 1a (99% ee) with B2nep2 (B2nep2 =5,5,5′,5′-tetramethyl-2,2′-bi-1,3,2-dioxaborinane). After a systematic optimization of the reaction conditions,[12] we found that a cocktail containing Ni(COD)2 (7.5 mol%), PCy3 (7.5 mol%), CuF2 (30 mol%), and CsF (30 mol%) provided the best results at 50 °C, affording 2a in 95% yield and 95% ees (Table [1], entry 1).[13] HPLC analysis revealed that the borylation event occurred with a neat retention of configuration. As expected, an intimate interplay of all reaction parameters was critical for success (Table [1], entries 2–7). For instance, while the presence of CsF or CuF2 was not absolutely required, their inclusion led to improved yields and enantioselectivities (Table [1], entries 11 and 12).[14] The latter is particularly noteworthy, indicating that nickel and copper salts might cooperatively promote the targeted C–O bond cleavage/C–B bond formation in high yields and excellent stereochemical fidelity under mild reaction conditions.[15] As expected, the nature of the ligand exerted a profound influence on the reaction outcome, with PCy3 providing the best results (Table [1], entries 2–5). Note, however, that a slight increase on the catalyst loading of PCy3 had a deleterious effect, obtaining 2a in lower yields (Table [1], entry 8). Intriguingly, no reaction took place in the absence of ligand (Table [1], entry 14) whereas lower reactivity was found when using more sterically encumbered B2pin2 as the boron source. Control experiments in the absence of Ni(COD)2 revealed that no borylation occurred, recovering quantitatively 1a in 99% ee (Table [1], entry 17).
Bolstered by these initial results, we next turned our attention to study the generality of our stereoselective borylation via C–O bond cleavage of benzyl ester derivatives (Scheme [3]). As shown, a host of differently substituted enantioenriched benzyl pivalates, easily within reach from the corresponding benzyl alcohols obtained via Corey–Bakshi–Shibata (CBS) reduction,[16] delivered the targeted compounds in good yields and enantioselectivities. The reaction worked equally well regardless of whether electron-rich (2b) or electron-poor substituents were included on the aryl backbone (2c). Unfortunately, the employment of quinoline (2e) or phenanthrene analogues (2f) resulted in a markedly loss of enantiomeric excess; while the former might suggest competitive binding of the nitrogen atom to the metal center, the loss of fidelity in the latter can tentatively be ascribed to racemization of the enantioenriched oxidative addition species by bimolecular mechanisms with exogeneous low-valent Ni(0)Ln.[5e] Substrates possessing aliphatic side chains other than methyl groups resulted in lower enantioselectivities (2h–m). These observations suggest that transmetalation might be hampered by the presence of larger alkyl side chains, setting the basis for the low yields are tentatively attributed to parasitic β-hydride elimination events that might erode the chiral integrity by subsequent migratory insertion. In line with this notion, non-negligible amounts of homobenzyl borylation were observed in the crude reaction mixtures. Unfortunately, non-π-extended aryl pivalates were not suited as substrates for the targeted borylation event.[17]
Independently on the starting precursor utilized, the borylation of 1a–m invariably occurred with a neat retention of configuration. This observation was corroborated by direct comparison of the alcohols obtained by oxidation of 1a–m with authentic samples obtained by CBS reduction of the corresponding ketone derivatives. Taking into consideration that both transmetalation and reductive elimination should proceed with stereoretention,[18] our results suggest a scenario consisting of an initial oxidative addition occurring with retention of configuration. In line with recent literature reports,[6a] [5f] we propose that the pivalate motif initially binds the nickel catalyst, setting the stage for a directed SN2′ oxidative addition that generate a putative π-benzyl nickel(II) intermediate I (Scheme [4], top). Such observation tacitly explains the considerably higher reactivity of extended π-systems, as partial dearomatization is required en route to the corresponding π-benzyl species I. In line with this notion, little reactivity, if any, was found with regular arenes, a recurrent limitation found in a myriad of catalytic C–O bond-functionalization technologies.[19] [20] Consistent with a SN2′ oxidative addition by attack of the Ni(0)Ln at the ortho position, we found that benzyl pivalates containing ortho substituents (1n,o) failed to provide the targeted benzyl boronate intermediates. In these cases, a site selectivity switch en route to linear boronic esters 2n and 2o was obtained (Scheme [4], bottom). The formation of these products likely arises from a sequence consisting of a β-hydride elimination followed by a migratory insertion prior to a final C–B bond-forming reaction that takes place selectively at the periphery to avoid the clash with the proximal ortho substituent on the arene.
Prompted by the pivotal role of organoboron reagents as synthetic intermediates,[11] we next turned our attention to study the prospective impact of this protocol by exploring the reactivity of the corresponding benzyl boronic ester intermediates (Scheme [5]). Among the different alternatives, we found that in situ generated 2a could trigger a Suzuki–Miyaura reaction[21] with a catalytic protocol based on Pd2(dba)3/PPh3,[22] resulting in the formation of 3 in excellent overall yield from (S)-1a, thus constituting an alternative to existing methodologies for the preparation of enantioenriched diarylmethanes. Consistent with a well-precedented stereoretentive transmetalation,[18] the C–C bond formation occurred with retention of configuration. Inspired by the reaction conditions reported by Zweifel,[23] we next wondered whether α-vinyl arenes could be within reach from 2a. As shown in Scheme [4] (bottom, right), this turned out to be the case. Specifically, we found that a simple exposure of in situ generated 2a to vinylmagnesium bromide followed by addition of I2 and NaOMe/MeOH at –78 °C resulted in 4 in good overall yield and exquisite stereochemical fidelity.
In summary, we have developed a stereospecific nickel-catalyzed borylation of enantioenriched benzyl pivalates with neat retention of configuration.[24] This method is characterized by the cooperativity of Cu and Ni salts to effect the targeted C–B bond-forming event with excellent stereochemical fidelity by a mechanism consistent with a stereoretentive oxidative addition. This work constitutes the first C–heteroatom bond formation from enantioenriched benzyl ester derivatives. Current investigations are focused on extending the scope of these reactions beyond C–B bond-forming reactions.
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Acknowledgment
C. Zárate and R. Martin-Montero thank MINECO and La Caixa Foundation for predoctoral fellowships.
Supporting Information
- Supporting information for this article is available online at https://doi-org.accesdistant.sorbonne-universite.fr/10.1055/s-0036-1590962.
- Supporting Information
-
References and Notes
- 1a Zarate C. Van Gemmeren M. Somerville RJ. Martin R. Adv. Organomet. Chem. 2016; 66: 143
- 1b Tollefson EJ. Hanna LE. Jarvo ER. Acc. Chem. Res. 2015; 47: 2344
- 1c Su B. Cao Z.-C. Shi Z.-J. Acc. Chem. Res. 2015; 48: 886
- 1d Tobisu M. Chatani N. Acc. Chem. Res. 2015; 48: 1717
- 1e Cornella J. Zarate C. Martin R. Chem. Soc. Rev. 2014; 43: 8081
- 1f Yamaguchi J. Muto K. Itami K. Eur. J. Org. Chem. 2013; 19
- 1g Rosen BM. Quasdorf KW. Wilson DA. Zhang N. Resmerita A.-M. Garg N. Percec V. Chem. Rev. 2011; 111: 1346
- 2a Cornella J. Jackson EP. Martin R. Angew. Chem. Int. Ed. 2015; 54: 4075
- 2b Oelke AJ. Jianwei S. Fu GC. J. Am. Chem. Soc. 2012; 134: 2966
- 3 Chenery AH. Kadunce NT. Reisman SE. Chem. Rev. 2015; 115: 9587
- 4 Eliel EL. Wilen SH. Stereochemistry of Organic Compounds . John Wiley and Sons; New York: 1994
- 5a Erickson LW. Lucas EL. Tollefson EJ. Jarvo ER. J. Am. Chem. Soc. 2016; 138: 14006
- 5b Konev MO. Hanna LE. Jarvo ER. Angew. Chem. Int. Ed. 2016; 55: 6730
- 5c Tollefson EJ. Dawson DD. Osborne CA. Jarvo ER. J. Am. Chem. Soc. 2014; 136: 14951
- 5d Harris MR. Konev MO. Jarvo ER. J. Am. Chem. Soc. 2014; 136: 7825
- 5e Yonova IM. Johnson AG. Osborne CA. Moore CE. Morrissette NS. Jarvo ER. Angew. Chem. Int. Ed. 2014; 53: 2422
- 5f Harris MR. Hanna LE. Greene MA. Moore CE. Jarvo ER. J. Am. Chem. Soc. 2013; 135: 3303
- 5g Taylor BL. H. Swift EC. Waetzig JD. Jarvo ER. J. Am. Chem. Soc. 2011; 133: 389
- 6a Zhou Q. Cobb KM. Tan T. Watson MP. J. Am. Chem. Soc. 2016; 138: 12057
- 6b Zhou Q. Srnivas HD. Zhang S. Watson MP. J. Am. Chem. Soc. 2016; 138: 11989
- 6c Srnivas HD. Zhou Q. Watson MP. Org. Lett. 2014; 16: 3596
- 6d Zhou Q. Srinivas HD. Dasgupta S. Watson MP. J. Am. Chem. Soc. 2013; 135: 3307
- 7a Zarate C. Nakajima M. Martin R. J. Am. Chem. Soc. 2017; 139: 1191
- 7b Zarate C. Manzano R. Martin R. J. Am. Chem. Soc. 2015; 137: 6754
- 7c Zarate CM. Martin R. J. Am. Chem. Soc. 2014; 136: 7253
- 7d Tobisu M. Yasutome A. Yamakawa A. Yamakawa K. Shimasaki T. Chatani N. Tetrahedron 2012; 68: 5157
- 7e Tobisu M. Shimasaki T. Chatani N. Chem. Lett. 2009; 38: 710
- 8a Zhu X. Chiba S. Chem. Soc. Rev. 2016; 45: 4504
- 8b Surry DS. Buchwald SL. Chem. Sci. 2011; 2: 27
- 8c Catalyzed Carbon-Heteroatom Bond-Formation . Yudin AK. Wiley-VCH; Weinheim: 2010
- 8d Hartwig JF. Nature 2008; 455: 314
- 9 Tobisu M. Zhao J. Kinuta H. Furukawa T. Igarashi T. Chatani N. Adv. Synth. Catal. 2016; 358: 2417
- 10a ref. 2a and 7a,b.
- 10b Gu Y. Martin R. Angew. Chem. Int. Ed. 2017; 56: 3187
- 10c Correa A. Martin R. J. Am. Chem. Soc. 2014; 136: 7253
- 10d Correa A. León T. Martin R. J. Am. Chem. Soc. 2014; 136: 1062
- 10e Alvarez-Bercedo P. Martin R. J. Am. Chem. Soc. 2010; 132: 17352
- 10f Cornella J. Martin R. Org. Lett. 2013; 15: 6298
- 10g Cornella J. Gómez-Bengoa E. Martin R. J. Am. Chem. Soc. 2013; 135: 1997
- 11a Sandford C. Aggarwal VK. Chem. Commun. 2017; 53: 5481
- 11b Hall DG. Boronic Acids . Wiley-VCH; Weinheim: 2005
- 12 For details, see Supporting Information.
- 13 The mass balance of the reaction accounts for the formation of 2-ethylnaphthalene via protodeborylation and the corresponding homobenzylboronic ester obtained from the putative oxidative addition species by a β-hydride elimination/migratory insertion prior C–B bond formation at the terminal position.
- 14 The synergistic use of CuF2 and low-valent nickel species was initially demonstrated by our group when forging C–Si bonds, see ref. 7c. For the beneficial role of CsF in recent C–O bond-cleavage procedures, see: Schwarzer MC. Konno R. Hojo T. Ohtsuki A. Nakamura K. Yasutome A. Takahashi H. Shimasaki T. Tobisu M. Chatani N. Mori S. J. Am. Chem. Soc. 2017; 139: 10347
- 15a Gou L. Chatupheeraphat A. Rueping M. Angew. Chem. Int. Ed. 2016; 55: 11810
- 15b Semba K. Ohtagaki Y. Nakao Y. Org. Lett. 2016; 18: 3956
- 15c Pu X. Hu J. Zhao Y. Shi Z. ACS Catal. 2016; 6: 6692
- 16 Bakshi RK. Shibata S. Chen C. Singh VK. Corey EJ. J. Am. Chem. Soc. 1987; 109: 7925
- 17 Recovered starting material was observed when employing non-π-extended aryl pivalates.
- 18a Netherton MR. Fu GC. Angew. Chem. Int. Ed. 2002; 41: 3910
- 18b Stille JK. In The Chemistry of the Metal–Carbon Bond . Vol. 2. Hartley FR. Patai S. John Wiley and Sons; New York: 1985: 625
- 19a Guo L. Liu X. Baumann C. Rueping M. Angew. Chem. Int. Ed. 2016; 55: 15415
- 19b Zhao Y. Snieckus V. J. Am. Chem. Soc. 2014; 136: 11224
- 19c Yu D.-G. Shi Z.-J. Angew. Chem. Int. Ed. 2011; 50: 7097
- 19d Tobisu M. Yamakawa K. Shimasaki T. Chatani N. Chem. Commun. 2011; 47: 2946
- 19e Yu DG. Li BJ. Zheng SF. Guan BT. Wang BQ. Shi ZJ. Angew. Chem. Int. Ed. 2010; 49: 4566
- 19f Alvarez-Bercedo R. Martin R. J. Am. Chem. Soc. 2010; 132: 17352
- 19g Tobisu M. Shimasaki T. Chatani N. Angew. Chem. Int. Ed. 2008; 47: 4866
- 20 η2-Coordination of π-extended systems to low-valent metal complexes is known to be stronger than regular arenes due to the partial preservation of the aromaticity: Bauer DJ. Krueger C. Inorg. Chem. 1977; 16: 884
- 21 Martin R. Buchwald SL. Acc. Chem. Res. 2008; 41: 1461
- 22 Imao D. Glasspole BW. Laberge VS. Crudden CM. J. Am. Chem. Soc. 1987; 109: 4756
- 23a Zweifel G. Arzoumanian H. Whitney CC. J. Am. Chem. Soc. 1967; 89: 3652
- 23b Evans A. Crawford TC. Thomas RC. Walker JA. J. Org. Chem. 1976; 41: 3947
- 23c Sonawane RP. Jheengut V. Rabalakos C. Larouche-Gauthier R. Scott HK. Aggarwal VK. Angew. Chem. Int. Ed. 2011; 50: 3760
- 24 (R)-1-(6-fluoronaphthalen-2-yl)ethanol (2d) – Typical ProcedureA 5 mL oven-dried screw-capped test tube containing a stirring bar was charged with the benzyl pivalate 1d (54.8 mg, 0.2 mmol). The test tube was introduced in an argon-filled glovebox where B2nep2 (67.8 mg, 0.3 mmol, 1.5 equiv), CuF2 (6 mg, 30 mol%), CsF (9.1 mg, 30 mol%), Ni(COD)2 (304 μL, 7.5 mol%, 0.05 M in toluene), PCy3 (152 μL, 7.5 mol%, 0.1 M), and toluene (1 mL) were then added sequentially. The tube with the mixture was taken out of the glovebox and stirred at 50 °C for 15 h. The mixture was then allowed to warm to room temperature, diluted with EtOAc (5 mL), and filtered through a Celite® plug, eluting with additional EtOAc (5mL). The filtrate was concentrated removing the volatiles. Then the reaction was cooled to 0 °C (water/ice bath) and BHT (ca. 1 mg) was added followed by anhydrous THF (1 mL). An ice-cold degassed mixture of 3 M NaOH (1.2 mL) and 30% aq H2O2 (0.75 mL) was added all at once. The reaction mixture was stirred at room temperature for 2 h. Then, the reaction mixture was diluted with water (4 mL) and extracted with Et2O (3 × 10 mL). The combined organic layers were washed with brine and dried over MgSO4. The filtrate was concentrated and purified by silica gel chromatography to give the title product 2d (30.5 mg, 80%) as a white solid (mp 84–86 °C). The enantiomeric excess was determined to be 65% ee (88% ees) by chiral HPLC analysis (CHIRALPAK IB, 1 mL/min, 2% EtOH/hexane, λ = 220 nm): t R (minor) = 12.4 min, t R (major) = 13.9 min. [α]D 24 = 43.2 (c 0.06, CHCl3).1H NMR (500 MHz, CDCl3): δ = 7.83–7.76 (m, 3 H), 7.53 (dd, J = 2.0 Hz, 1 H), 7.44 (dd, J = 2.6 Hz, 1 H), 7.26 (td, J = 2.6 Hz, 1 H), 5.06 (q, J = 6.4 Hz, 1 H), 1.97 (s, 1 H, OH), 1.58 (d, J = 6.4 Hz, 3 H) ppm. 13C NMR (126 MHz, CDCl3): δ = 161.8, 159.4, 142.5, 133.6, 130.3, 127.7, 124.9, 123.8, 116.6, 110.7, 70.3, 25.2 ppm. 19F NMR (376 MHz, CDCl3): δ = –115.1 ppm.
For selected enantioselective, rather than stereospecific, cross-coupling reactions of C–O electrophiles other than particularly activated organic sulfonates, see:
For selected references, see:
For selected comprehensive reviews on C–heteroatom bond-forming reactions:
Selected references:
For recent examples of Ni/Cu cooperativity for effecting C–heteroatom bond-forming reactions, see:
For selected references limited to π-extended systems or to the presence of ortho- or para-activating groups, see:
-
References and Notes
- 1a Zarate C. Van Gemmeren M. Somerville RJ. Martin R. Adv. Organomet. Chem. 2016; 66: 143
- 1b Tollefson EJ. Hanna LE. Jarvo ER. Acc. Chem. Res. 2015; 47: 2344
- 1c Su B. Cao Z.-C. Shi Z.-J. Acc. Chem. Res. 2015; 48: 886
- 1d Tobisu M. Chatani N. Acc. Chem. Res. 2015; 48: 1717
- 1e Cornella J. Zarate C. Martin R. Chem. Soc. Rev. 2014; 43: 8081
- 1f Yamaguchi J. Muto K. Itami K. Eur. J. Org. Chem. 2013; 19
- 1g Rosen BM. Quasdorf KW. Wilson DA. Zhang N. Resmerita A.-M. Garg N. Percec V. Chem. Rev. 2011; 111: 1346
- 2a Cornella J. Jackson EP. Martin R. Angew. Chem. Int. Ed. 2015; 54: 4075
- 2b Oelke AJ. Jianwei S. Fu GC. J. Am. Chem. Soc. 2012; 134: 2966
- 3 Chenery AH. Kadunce NT. Reisman SE. Chem. Rev. 2015; 115: 9587
- 4 Eliel EL. Wilen SH. Stereochemistry of Organic Compounds . John Wiley and Sons; New York: 1994
- 5a Erickson LW. Lucas EL. Tollefson EJ. Jarvo ER. J. Am. Chem. Soc. 2016; 138: 14006
- 5b Konev MO. Hanna LE. Jarvo ER. Angew. Chem. Int. Ed. 2016; 55: 6730
- 5c Tollefson EJ. Dawson DD. Osborne CA. Jarvo ER. J. Am. Chem. Soc. 2014; 136: 14951
- 5d Harris MR. Konev MO. Jarvo ER. J. Am. Chem. Soc. 2014; 136: 7825
- 5e Yonova IM. Johnson AG. Osborne CA. Moore CE. Morrissette NS. Jarvo ER. Angew. Chem. Int. Ed. 2014; 53: 2422
- 5f Harris MR. Hanna LE. Greene MA. Moore CE. Jarvo ER. J. Am. Chem. Soc. 2013; 135: 3303
- 5g Taylor BL. H. Swift EC. Waetzig JD. Jarvo ER. J. Am. Chem. Soc. 2011; 133: 389
- 6a Zhou Q. Cobb KM. Tan T. Watson MP. J. Am. Chem. Soc. 2016; 138: 12057
- 6b Zhou Q. Srnivas HD. Zhang S. Watson MP. J. Am. Chem. Soc. 2016; 138: 11989
- 6c Srnivas HD. Zhou Q. Watson MP. Org. Lett. 2014; 16: 3596
- 6d Zhou Q. Srinivas HD. Dasgupta S. Watson MP. J. Am. Chem. Soc. 2013; 135: 3307
- 7a Zarate C. Nakajima M. Martin R. J. Am. Chem. Soc. 2017; 139: 1191
- 7b Zarate C. Manzano R. Martin R. J. Am. Chem. Soc. 2015; 137: 6754
- 7c Zarate CM. Martin R. J. Am. Chem. Soc. 2014; 136: 7253
- 7d Tobisu M. Yasutome A. Yamakawa A. Yamakawa K. Shimasaki T. Chatani N. Tetrahedron 2012; 68: 5157
- 7e Tobisu M. Shimasaki T. Chatani N. Chem. Lett. 2009; 38: 710
- 8a Zhu X. Chiba S. Chem. Soc. Rev. 2016; 45: 4504
- 8b Surry DS. Buchwald SL. Chem. Sci. 2011; 2: 27
- 8c Catalyzed Carbon-Heteroatom Bond-Formation . Yudin AK. Wiley-VCH; Weinheim: 2010
- 8d Hartwig JF. Nature 2008; 455: 314
- 9 Tobisu M. Zhao J. Kinuta H. Furukawa T. Igarashi T. Chatani N. Adv. Synth. Catal. 2016; 358: 2417
- 10a ref. 2a and 7a,b.
- 10b Gu Y. Martin R. Angew. Chem. Int. Ed. 2017; 56: 3187
- 10c Correa A. Martin R. J. Am. Chem. Soc. 2014; 136: 7253
- 10d Correa A. León T. Martin R. J. Am. Chem. Soc. 2014; 136: 1062
- 10e Alvarez-Bercedo P. Martin R. J. Am. Chem. Soc. 2010; 132: 17352
- 10f Cornella J. Martin R. Org. Lett. 2013; 15: 6298
- 10g Cornella J. Gómez-Bengoa E. Martin R. J. Am. Chem. Soc. 2013; 135: 1997
- 11a Sandford C. Aggarwal VK. Chem. Commun. 2017; 53: 5481
- 11b Hall DG. Boronic Acids . Wiley-VCH; Weinheim: 2005
- 12 For details, see Supporting Information.
- 13 The mass balance of the reaction accounts for the formation of 2-ethylnaphthalene via protodeborylation and the corresponding homobenzylboronic ester obtained from the putative oxidative addition species by a β-hydride elimination/migratory insertion prior C–B bond formation at the terminal position.
- 14 The synergistic use of CuF2 and low-valent nickel species was initially demonstrated by our group when forging C–Si bonds, see ref. 7c. For the beneficial role of CsF in recent C–O bond-cleavage procedures, see: Schwarzer MC. Konno R. Hojo T. Ohtsuki A. Nakamura K. Yasutome A. Takahashi H. Shimasaki T. Tobisu M. Chatani N. Mori S. J. Am. Chem. Soc. 2017; 139: 10347
- 15a Gou L. Chatupheeraphat A. Rueping M. Angew. Chem. Int. Ed. 2016; 55: 11810
- 15b Semba K. Ohtagaki Y. Nakao Y. Org. Lett. 2016; 18: 3956
- 15c Pu X. Hu J. Zhao Y. Shi Z. ACS Catal. 2016; 6: 6692
- 16 Bakshi RK. Shibata S. Chen C. Singh VK. Corey EJ. J. Am. Chem. Soc. 1987; 109: 7925
- 17 Recovered starting material was observed when employing non-π-extended aryl pivalates.
- 18a Netherton MR. Fu GC. Angew. Chem. Int. Ed. 2002; 41: 3910
- 18b Stille JK. In The Chemistry of the Metal–Carbon Bond . Vol. 2. Hartley FR. Patai S. John Wiley and Sons; New York: 1985: 625
- 19a Guo L. Liu X. Baumann C. Rueping M. Angew. Chem. Int. Ed. 2016; 55: 15415
- 19b Zhao Y. Snieckus V. J. Am. Chem. Soc. 2014; 136: 11224
- 19c Yu D.-G. Shi Z.-J. Angew. Chem. Int. Ed. 2011; 50: 7097
- 19d Tobisu M. Yamakawa K. Shimasaki T. Chatani N. Chem. Commun. 2011; 47: 2946
- 19e Yu DG. Li BJ. Zheng SF. Guan BT. Wang BQ. Shi ZJ. Angew. Chem. Int. Ed. 2010; 49: 4566
- 19f Alvarez-Bercedo R. Martin R. J. Am. Chem. Soc. 2010; 132: 17352
- 19g Tobisu M. Shimasaki T. Chatani N. Angew. Chem. Int. Ed. 2008; 47: 4866
- 20 η2-Coordination of π-extended systems to low-valent metal complexes is known to be stronger than regular arenes due to the partial preservation of the aromaticity: Bauer DJ. Krueger C. Inorg. Chem. 1977; 16: 884
- 21 Martin R. Buchwald SL. Acc. Chem. Res. 2008; 41: 1461
- 22 Imao D. Glasspole BW. Laberge VS. Crudden CM. J. Am. Chem. Soc. 1987; 109: 4756
- 23a Zweifel G. Arzoumanian H. Whitney CC. J. Am. Chem. Soc. 1967; 89: 3652
- 23b Evans A. Crawford TC. Thomas RC. Walker JA. J. Org. Chem. 1976; 41: 3947
- 23c Sonawane RP. Jheengut V. Rabalakos C. Larouche-Gauthier R. Scott HK. Aggarwal VK. Angew. Chem. Int. Ed. 2011; 50: 3760
- 24 (R)-1-(6-fluoronaphthalen-2-yl)ethanol (2d) – Typical ProcedureA 5 mL oven-dried screw-capped test tube containing a stirring bar was charged with the benzyl pivalate 1d (54.8 mg, 0.2 mmol). The test tube was introduced in an argon-filled glovebox where B2nep2 (67.8 mg, 0.3 mmol, 1.5 equiv), CuF2 (6 mg, 30 mol%), CsF (9.1 mg, 30 mol%), Ni(COD)2 (304 μL, 7.5 mol%, 0.05 M in toluene), PCy3 (152 μL, 7.5 mol%, 0.1 M), and toluene (1 mL) were then added sequentially. The tube with the mixture was taken out of the glovebox and stirred at 50 °C for 15 h. The mixture was then allowed to warm to room temperature, diluted with EtOAc (5 mL), and filtered through a Celite® plug, eluting with additional EtOAc (5mL). The filtrate was concentrated removing the volatiles. Then the reaction was cooled to 0 °C (water/ice bath) and BHT (ca. 1 mg) was added followed by anhydrous THF (1 mL). An ice-cold degassed mixture of 3 M NaOH (1.2 mL) and 30% aq H2O2 (0.75 mL) was added all at once. The reaction mixture was stirred at room temperature for 2 h. Then, the reaction mixture was diluted with water (4 mL) and extracted with Et2O (3 × 10 mL). The combined organic layers were washed with brine and dried over MgSO4. The filtrate was concentrated and purified by silica gel chromatography to give the title product 2d (30.5 mg, 80%) as a white solid (mp 84–86 °C). The enantiomeric excess was determined to be 65% ee (88% ees) by chiral HPLC analysis (CHIRALPAK IB, 1 mL/min, 2% EtOH/hexane, λ = 220 nm): t R (minor) = 12.4 min, t R (major) = 13.9 min. [α]D 24 = 43.2 (c 0.06, CHCl3).1H NMR (500 MHz, CDCl3): δ = 7.83–7.76 (m, 3 H), 7.53 (dd, J = 2.0 Hz, 1 H), 7.44 (dd, J = 2.6 Hz, 1 H), 7.26 (td, J = 2.6 Hz, 1 H), 5.06 (q, J = 6.4 Hz, 1 H), 1.97 (s, 1 H, OH), 1.58 (d, J = 6.4 Hz, 3 H) ppm. 13C NMR (126 MHz, CDCl3): δ = 161.8, 159.4, 142.5, 133.6, 130.3, 127.7, 124.9, 123.8, 116.6, 110.7, 70.3, 25.2 ppm. 19F NMR (376 MHz, CDCl3): δ = –115.1 ppm.
For selected enantioselective, rather than stereospecific, cross-coupling reactions of C–O electrophiles other than particularly activated organic sulfonates, see:
For selected references, see:
For selected comprehensive reviews on C–heteroatom bond-forming reactions:
Selected references:
For recent examples of Ni/Cu cooperativity for effecting C–heteroatom bond-forming reactions, see:
For selected references limited to π-extended systems or to the presence of ortho- or para-activating groups, see:
