Letter pubs.acs.org/acscatalysis
Ketene Aminal Phosphates: Competent Substrates for Enantioselective Pd(0)-Catalyzed C−H Functionalizations Daria Grosheva and Nicolai Cramer* Laboratory of Asymmetric Catalysis and Synthesis, Institute of Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne, EPFL SB ISIC LCSA, BCH 4305, CH-1015 Lausanne, Switzerland S Supporting Information *
ABSTRACT: Enantioselective Pd(0)-catalyzed C−H functionalizations of ketene aminal phosphates provide isoindoline scaffolds with high enantioselectivity at ambient temperature. The high level of enantiocontrol is enabled by a tailored monodentate electron-rich phosphine ligand featuring a pointchiral phospholane module and a bulky atropchiral binaphthyl backbone. KEYWORDS: asymmetric catalysis, C−H functionalization, palladium, ligand design, enantioselectivity
A
mong nitrogen-containing heterocycles, indolizidine alkaloids are an important class of natural products, displaying a very broad range of biological activities (Figure 1).1
Scheme 1. Enantioselective C−H Functionalizations of Ketene Aminal Phosphates
Figure 1. Selected examples of indolizidine alkaloids.
chloride, are stable compounds.14 They have been used for few Pd-catalyzed couplings, suggesting their potential suitability for C−H functionalizations.14−16 The influence of chiral phosphate counterions on the enantioselectivity of a Pd-catalyzed CMDprocess was recently reported by Baudoin et al.10n Therefore, the behavior of a built-in phosphate moiety in the electrophile is an intriguing additional query. Could it directly serve as competent coordinated base for the CMD step? Herein, we report a Pd(0)-catalyzed enantioselective C−H functionalization of ketene aminal phosphates providing access to chiral isoindolines. Oxidative addition of alkenyl phosphates to Pd(0) complexes at ambient temperature is accelerated by electron-rich phosphine ligands. We have previously reported the SagePhos ligands combining an 2′,6′-dialkoxybiaryl core with the C2symmetric electron-rich phospholane moiety.10e An additional modification handle to further tune the selectivity and reactivity would be highly desirable. In this context, merging the pointchiral dimethyl phospholane module with the powerful atropchiral biaryl unit of the MOP ligand would result in a modular and tunable ligand class (Scheme 2).
Consequently, different synthetic strategies for the construction of the indolizidine scaffold have been developed,2,3 but only few of them are catalytic enantioselective methods. These consist of metal-catalyzed [2+2+2]-cycloadditions,4 allylic aminations,5 Heck-cyclizations,6 and organocatalytic transformations.7 An efficient C−H functionalization is lacking and would be a valuable complementary strategy. Metal-catalyzed C−H functionalizations have become powerful tools for the rapid generation of structural complexity from simple precursors.8,9 For instance, a variety of enantioselective Pd(0)-catalyzed transformations to access nitrogen-containing heterocycles using direct arylation strategies have been developed.10,11 While a strong focus has been placed on different C−H bonds toward functionalization, the electrophilic part consisted mainly of aryl bromides, iodides, and triflates. Surprisingly, related C−H alkenylations remain far less developed. Scattered reports utilize alkenyl bromides12 or alkenyl triflates.13 Our envisioned asymmetric functionalization to access the indolizidine core required an elaborate ketene aminal electrophile (Scheme 1). Ketene aminal triflates are unstable and rapidly decompose upon isolation attempts. In stark contrast, related ketene aminal phosphates, accessible by deprotonation of imides and trapping with a phosphoryl © XXXX American Chemical Society
Received: August 16, 2017 Revised: September 22, 2017 Published: September 26, 2017 7417
DOI: 10.1021/acscatal.7b02783 ACS Catal. 2017, 7, 7417−7420
Letter
ACS Catalysis Scheme 2. Merging the Design of SagePhos and MOP
Table 1. Optimization of the Enantioselective Ketene Aminal Phosphate Cyclizationa
The methoxy-substituted derivative L1 is known;17 however, its previous synthesis is low yielding and rather inconvenient, largely due to a sensitive intermediate primary phosphane. We were aiming for a route with an emphasis on flexibility with respect to the introduction of the substituent R on the lower ring and stable secondary phospholane oxide 2 as chiral module (Scheme 3). In this context, Pd(0)-catalyzed coupling of binol Scheme 3. Synthesis of the Ligands L1−L8
entry
[Pd]
L*
acid
2b
er
1 2 3 4 5 6 7 8 9 10 11c 12c 13 14 15 16 17 18d 19d,e 20f
Pd(dba)2 Pd(dba)2 Pd(dba)2 Pd(dba)2 Pd(dba)2 Pd(dba)2 Pd(dba)2 Pd(dba)2 Pd(dba)2 Pd(dba)2 Pd(dba)2 Pd(dba)2 Pd(dba)2 Pd(dba)2 Pd(dba)2 Pd(OAc)2 Pd(OPiv)2 Pd(OPiv)2 Pd(OPiv)2 Pd(OPiv)2
L9 L10 L1 L2 L3 L4 L5 L6 L7 L8 L11 L12 L6 L6 L6 L6 L6 L6 L6 L6
Ph2MeCCO2H Ph2MeCCO2H Ph2MeCCO2H Ph2MeCCO2H Ph2MeCCO2H Ph2MeCCO2H Ph2MeCCO2H Ph2MeCCO2H Ph2MeCCO2H Ph2MeCCO2H Ph2MeCCO2H Ph2MeCCO2H PhCO2H PivOH − PivOH − PivOH PivOH PivOH
19% 82% 78% 65% 48% 32% 16% 29% 43% 38% 12% 60% 37% 36% 21% 82% 90% 93% 8% 80%g
51:49 89:11 78.5:21.5 87:13 87:13 90:10 77.5:12.5 90.5:9.5 70:30 86.5:13.5 70.5:29.5 79.5:20.5 93:7 93.5:6.5 73:27 75.5:24.5 92:8 94.5:5.5 nd 95.5:4.5
a Conditions: 0.05 mmol 1a, 20 mol % acid, 1.5 equiv of Cs2CO3, 0.1 M in toluene for 14 h at 40 °C. bDetermined by 1H NMR with an internal standard. cAt 80 °C. dWith 5 mol % [Pd], 10 mol % L* at 0.5 M concentration and 23 °C. e1a′ instead of 1a at 80 °C. f5 mmol 1a [2.56 g], 5 mol % Pd(OPiv)2, 10 mol % L6, 7.5 mmol Cs2CO3, 0.5 M in toluene, 48 h. gIsolated yield.
bistriflate 1 with 2 provided selectively monocoupled phosphine oxide.18 After saponification of the remaining OTf residue, the revealed hydroxyl group of 3 was alkylated or silylated with a group of variable steric demand. A final reduction of phosphine oxide with Cl3SiH provided phosphine ligands L2−L8. Overall, the route proved to be scalable and reproducible and provided as well access to ligand diastereomers L7 and L8. Ketene aminal phosphate 4a was used as the prototype substrate for the enantioselective arylation and to evaluate the influence of the different ligands and reaction parameters (Table 1, for additional optimization studies, see SI). The axial chiral Cy-MOP ligand (L9) provided 5a in low yield and a very low enantioselectivity of 51:49 er (entry 1). SagePhos (L10) was significantly more reactive and selective (89:11 er) (entry 2). The phospholane ligands L1−L6 showed a general trend: increasing the steric demand of the substituent R provided higher enantioselectivities, accompanied by a loss in reactivity, with TBDPS-substituted L6 being the most selective (entries 3−8). The dominant portion of the enantioselectivity arose from the phospholane unit, while the axial chirality played a minor role. Nevertheless, ligands L7 and L8 with opposite configuration of the axial stereogenic centers were the
mismatched combination and resulted in lower enantioselectivity (entries 9 and 10). In comparison, taddol-derived phosphoramidites L11 and L12 that have provided for a number of highly enantioselective Pd(0)-catalyzed C−H functionalizations,19 were not suitable. These ligands required a higher reaction temperature and, in addition, displayed only modest enantiocontrol (entries 11−12). Pivalic acid gave superior results, compared to other carboxylic acids (entries 6, 13−14). Carboxylate-free conditions (no external carboxylic acid and carboxylate free Pd-source) were significantly inferior in terms of conversion and enantioselectivity (entry 15). This finding suggests that the diphenyl phosphate anion is a poor promotor of the CMD in comparison to a carboxylate. Cesium carbonate was the base of choice (for detailed optimization studies, see SI). Among the Pd sources that were screened, Pd(OPiv)2 was optimal in terms of both reactivity and enantioselectivity (entries 14, 16−17). Supplementing the pivalate content originating from Pd(OPiv)2 with 20 mol % pivalic acid allows reduction of the catalyst loading to 5 mol % with a simultaneous reduction of the reaction temperature to 7418
DOI: 10.1021/acscatal.7b02783 ACS Catal. 2017, 7, 7417−7420
Letter
ACS Catalysis 23 °C (entry 18). The substituents of the phosphate ester have a large impact on the reactivity. In contrast to the diphenyl phosphate 4a, diethyl phosphate 4a′ was largely inert, even at 80 °C (entry 19). The transformation scaled well and could be performed on a gram-scale (2.56 g of 4a) while retaining a good yield and enantioselectivity (entry 20). Next, we evaluated the scope of the transformation (Scheme 4). A wide range of para-substituted arene substrates reacted
electron-poor and electron-rich aryl groups react at relatively comparable rates, a parallel kinetic resolution of racemic substrates rac-4 bearing two different aryl groups was feasible (Table 2). Examples for parallel kinetic resolutions with C−H Table 2. Parallel Kinetic Resolution of Racemic Unsymmetrical Diaryl Ketene Aminal Phosphates 1a
Scheme 4. Scope of the Asymmetric Isoindoline Synthesisa
entry
4 (R)
yield 5 + 5′
5:5′
er 5
er 5′
1 2 3 4
4n (F) 4o (CF3) 4p (OMe) 4r (Me)
90% 96% 93% 94%
1:1.31 1:1.13 1:1.11 1:1.09
98:2 97.5:2.5 97:3 95:5
88:12 92:8 92:8 94.5:5.5
Conditions: 0.1 mmol 1, 5 μmol Pd(OPiv)2, 10 μmol L6, 20 μmol PivOH, 0.15 mmol Cs2CO3, 0.5 M at 23 °C for 14 h. a
functionalizations are scarce.10c,20 Regardless of the electronic bias of the targeted aryl groups (Ph vs electronically modified aryl), the functionalization operated in a complete regiodivergent fashion with remarkable levels of enantioselectivity. Both products 5 and 5′ were formed in very good yields and with high enantioselectivities of up to 98:2 er. Enamide 5a could be selectively hydrogenated (eq 1). Reduction with H2 and Pd/C occurred from the less-hindered
face, resulting in the formation of single diastereoisomer 6a. The lactam moiety of 6a could be further reduced with a nickel catalyst and PhSiH321 delivering indolizidine 7a. In summary, we have reported a flexible and modular route to sterically hindered monodentate phospholane ligands with atropchiral biaryl backbone. These ligands were key to the successful development of an enantioselective C−H alkenylation at ambient temperature. For the first time, ketene aminal phosphates are shown to be competent electrophiles in Pd(0)catalyzed C−H functionalizations. Moreover, the transformation was successfully extended to parallel kinetic resolutions.
Conditions: 0.1 mmol 1, 5 μmol Pd(OPiv)2, 10 μmol L6, 20 μmol PivOH, 0.15 mmol Cs2CO3, 0.5 M at 23 °C for 14 h; isolated yields. b 10 μmol Pd(OPiv)2, 20 μmol L6. cAt 60 °C. a
well and provided similarly high levels of enantioselectivity (5b−5g). Both electron-poor and electron-rich substrates furnished corresponding heterocycles in comparable yields with little electronic influence on the enantioselectivity (5f and 5g). Notably, an aryl chloride was tolerated and remained intact during the Pd-catalyzed functionalization, enabling the possibility for orthogonal cross-coupling reactions. Moreover, the absolute configuration of chlorinated product 5e was determined to be S by X-ray crystallographic analysis. Substrates bearing a meta-substituent reacted highly selectively with the less hindered ortho-C−H group (5h and 5i). orthoSubstitution (5k) was tolerated, although the reaction required higher temperature and was therefore less selective. Electronrich heterocycle-bearing substrates such as 4j reacted well and thienyl-substituted product 5j was obtained in high enantioselectivity. Seemingly remote and innocent modifications of the glutarimide-derived part of the substrates (4l and 4m) had little influence on the reactivity, but caused slightly lower selectivities for 5l and 5m. Next, we aimed to broaden the substrate range and to enhance the utility of the transformation. Having observed that
■
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acscatal.7b02783. Experimental procedures, analytical, and spectral data for all new compounds (PDF) X-ray data for L6 (CIF) X-ray data for 5e (CIF)
■
AUTHOR INFORMATION
Corresponding Author
*E-mail: nicolai.cramer@epfl.ch. ORCID
Nicolai Cramer: 0000-0001-5740-8494 7419
DOI: 10.1021/acscatal.7b02783 ACS Catal. 2017, 7, 7417−7420
Letter
ACS Catalysis Notes
7441. (c) Katayev, D.; Nakanishi, M.; Burgi, T.; Kundig, E. P. Chem. Sci. 2012, 3, 1422−1425. (d) Saget, T.; Lemouzy, S. J.; Cramer, N. Angew. Chem., Int. Ed. 2012, 51, 2238−2242. (e) Saget, T.; Cramer, N. Angew. Chem., Int. Ed. 2012, 51, 12842−12845. (f) Larionov, E.; Nakanishi, M.; Katayev, D.; Besnard, C.; Kundig, E. P. Chem. Sci. 2013, 4, 1995−2005. (g) Saget, T.; Cramer, N. Angew. Chem., Int. Ed. 2013, 52, 7865−7868. (h) Katayev, D.; Larionov, E.; Nakanishi, M.; Besnard, C.; Kündig, E. P. Chem. - Eur. J. 2014, 20, 15021−15030. (i) Liu, L.; Zhang, A.-A.; Zhao, R.-J.; Li, F.; Meng, T.-J.; Ishida, N.; Murakami, M.; Zhao, W.-X. Org. Lett. 2014, 16, 5336−5338. (j) Ma, X.; Gu, Z. RSC Adv. 2014, 4, 36241−36244. (k) Lin, Z.-Q.; Wang, W.-Z.; Yan, S.-B.; Duan, W.-L. Angew. Chem., Int. Ed. 2015, 54, 6265−6269. (l) Pedroni, J.; Saget, T.; Donets, P. A.; Cramer, N. Chem. Sci. 2015, 6, 5164−5171. (m) He, C.; Hou, M.; Zhu, Z.; Gu, Z. ACS Catal. 2017, 7, 5316−5320. (n) Yang, L.; Melot, R.; Neuburger, M.; Baudoin, O. Chem. Sci. 2017, 8, 1344−1349. (11) For related examples of enantioselective C−H imidoylation and carbamoylation reactions, see respectively: (a) Wang, J.; Gao, D.-W.; Huang, J.; Tang, S.; Xiong, Z.; Hu, H.; You, S.-L.; Zhu, Q. ACS Catal. 2017, 7, 3832−3836. (b) Dailler, D.; Rocaboy, R.; Baudoin, O. Angew. Chem., Int. Ed. 2017, 56, 7218−7222. (12) (a) Yagoubi, M.; Cruz, A. C. F.; Nichols, P. L.; Elliott, R. L.; Willis, M. C. Angew. Chem., Int. Ed. 2010, 49, 7958−7962. (b) SofackKreutzer, J.; Martin, N.; Renaudat, A.; Jazzar, R.; Baudoin, O. Angew. Chem., Int. Ed. 2012, 51, 10399−10402. (c) Dailler, D.; Danoun, G.; Baudoin, O. Angew. Chem., Int. Ed. 2015, 54, 4919−4922. (d) Dailler, D.; Danoun, G.; Ourri, B.; Baudoin, O. Chem. - Eur. J. 2015, 21, 9370− 9379. (e) Holstein, P. M.; Dailler, D.; Vantourout, J.; Shaya, J.; Millet, A.; Baudoin, O. Angew. Chem., Int. Ed. 2016, 55, 2805−2809. (f) Ladd, C. L.; Charette, A. B. Org. Lett. 2016, 18, 6046−6049. (13) (a) Willis, M. C.; Claverie, C. K.; Mahon, M. F. Chem. Commun. 2002, 832−833. (b) Cruz, A. C. F.; Miller, N. D.; Willis, M. C. Org. Lett. 2007, 9, 4391−4393. (c) Albicker, M. R.; Cramer, N. Angew. Chem., Int. Ed. 2009, 48, 9139−9142. (14) (a) Nicolaou, K. C.; Namoto, K. Chem. Commun. 1998, 1757− 1758. (b) Coe, J. W. Org. Lett. 2000, 2, 4205−4208. (c) Galbo, F. L.; Occhiato, E. G.; Guarna, A.; Faggi, C. J. Org. Chem. 2003, 68, 6360− 6368. (15) (a) Claveau, E.; Gillaizeau, I.; Blu, J.; Bruel, A.; Coudert, G. J. Org. Chem. 2007, 72, 4832−4836. (b) Fuwa, H.; Sasaki, M. Org. Lett. 2007, 9, 3347−3350. (c) Fuwa, H.; Sasaki, M. J. Org. Chem. 2009, 74, 212−221. (d) Cieslikiewicz, M.; Bouet, A.; Jugé, S.; Toffano, M.; Bayardon, J.; West, C.; Lewinski, K.; Gillaizeau, I. Eur. J. Org. Chem. 2012, 2012, 1101−1106. (e) Sallio, R.; Lebrun, S.; AgbossouNiedercorn, F.; Michon, C.; Deniau, E. Tetrahedron: Asymmetry 2012, 23, 998−1004. (f) Begliomini, S.; Sernissi, L.; Scarpi, D.; Occhiato, E. G. Eur. J. Org. Chem. 2014, 2014, 5448−5455. (16) For related C−H functionalizations of alkenyl and benzyl phosphates, see: Ackermann, L.; Barfüsser, S.; Pospech, J. Org. Lett. 2010, 12, 724−726. (17) Saha, B.; RajanBabu, T. V. J. Org. Chem. 2007, 72, 2357−2363. (18) The same strategy has been previously employed for the synthesis of BINOL-derived phosphines with an achiral phospholane core: Hamada, T.; Chieffi, A.; Åhman, J.; Buchwald, S. L. J. Am. Chem. Soc. 2002, 124, 1261−1268. (19) Pedroni, J.; Cramer, N. Chem. Commun. 2015, 51, 17647− 17657. (20) (a) Ducray, P.; Rousseau, B.; Mioskowski, C. J. Org. Chem. 1999, 64, 3800−3801. (b) Tanaka, K.; Fu, G. C. J. Am. Chem. Soc. 2003, 125, 8078−8079. (c) Tanaka, K.; Hagiwara, Y.; Hirano, M. Angew. Chem., Int. Ed. 2006, 45, 2734−2737. (d) Lee, T.; Wilson, T. W.; Berg, R.; Ryberg, P.; Hartwig, J. F. J. Am. Chem. Soc. 2015, 137, 6742−6745. (21) Ni-catalyzed reduction of amides: Simmons, B. J.; Hoffmann, M.; Hwang, J.; Jackl, M. K.; Garg, N. K. Org. Lett. 2017, 19, 1910− 1913.
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This work is supported by the Swiss National Science Foundation (no. 155967). We thank Dr. R. Scopelliti and Dr. F. Fadaei Tirani for X-ray crystallographic analysis of compounds L6 and 5e.
■
REFERENCES
(1) (a) Mensah-Dwumah, M.; Daly, J. W. Toxicon 1978, 16, 189− 194. (b) Daly, J. W., Garraffo, H. M., Spande, T. F. In Alkaloids: Chemical and Biological Perspectives, 1st ed.; Pelletier, S. W., Ed.; Pergamon: New York, 1999; Vol. 13, p 1. (2) Michael, J. P. Nat. Prod. Rep. 2008, 25, 139−165. (3) Selected recent synthesis of indolizidine alkaloids: (a) Smith, A. B.; Kim, D.-S. J. Org. Chem. 2006, 71, 2547−2557. (b) Kapat, A.; Nyfeler, E.; Giuffredi, G. T.; Renaud, P. J. Am. Chem. Soc. 2009, 131, 17746−17747. (c) Stoye, A.; Quandt, G.; Brunnhöfer, B.; Kapatsina, E.; Baron, J.; Fischer, A.; Weymann, M.; Kunz, H. Angew. Chem., Int. Ed. 2009, 48, 2228−2230. (d) Yang, D.; Micalizio, G. C. J. Am. Chem. Soc. 2009, 131, 17548−17549. (e) Kobayashi, T.; Hasegawa, F.; Hirose, Y.; Tanaka, K.; Mori, H.; Katsumura, S. J. Org. Chem. 2012, 77, 1812. (f) Pronin, S. V.; Tabor, M. G.; Jansen, D. J.; Shenvi, R. A. J. Am. Chem. Soc. 2012, 134, 2012−2015. (g) Ortega, N.; Tang, D.-T. D.; Urban, S.; Zhao, D.; Glorius, F. Angew. Chem., Int. Ed. 2013, 52, 9500− 9503. (4) (a) Lee, E. E.; Rovis, T. Org. Lett. 2008, 10, 1231−1234. (b) Dalton, D. M.; Oberg, K. M.; Yu, R. T.; Lee, E. E.; Perreault, S.; Oinen, M. E.; Pease, M. L.; Malik, G.; Rovis, T. J. Am. Chem. Soc. 2009, 131, 15717−15728. (c) Yu, R. T.; Lee, E. E.; Malik, G.; Rovis, T. Angew. Chem., Int. Ed. 2009, 48, 2379−2382. (5) Gärtner, M.; Weihofen, R.; Helmchen, G. Chem. - Eur. J. 2011, 17, 7605−7622. (6) Nukui, S.; Sodeoka, M.; Sasai, H.; Shibasaki, M. J. Org. Chem. 1995, 60, 398−404. (7) (a) Kondekar, N. B.; Kumar, P. Synthesis 2010, 2010, 3105−3112. (b) Panchgalle, S. P.; Bidwai, H. B.; Chavan, S. P.; Kalkote, U. R. Tetrahedron: Asymmetry 2010, 21, 2399−2401. (c) Abels, F.; Lindemann, C.; Koch, E.; Schneider, C. Org. Lett. 2012, 14, 5972− 5975. (d) Abels, F.; Lindemann, C.; Schneider, C. Chem. - Eur. J. 2014, 20, 1964−1979. (e) Tan, Y.; Chen, Y.-J.; Lin, H.; Luan, H.-L.; Sun, X.W.; Yang, X.-D.; Lin, G.-Q. Chem. Commun. 2014, 50, 15913−15915. (8) For recent reviews on transition-metal-catalyzed C−H functionalization, see: (a) Moselage, M.; Li, J.; Ackermann, L. ACS Catal. 2016, 6, 498−525. (b) Dong, Z.; Ren, Z.; Thompson, S. J.; Xu, Y.; Dong, G. Chem. Rev. 2017, 117, 9333−9403. (c) He, J.; Wasa, M.; Chan, K. S. L.; Shao, Q.; Yu, J.-Q. Chem. Rev. 2017, 117, 8754−8786. (d) Hummel, J. R.; Boerth, J. A.; Ellman, J. A. Chem. Rev. 2017, 117, 9163−9227. (e) Kim, D.-S.; Park, W.-J.; Jun, C.-H. Chem. Rev. 2017, 117, 8977− 9015. (f) Murakami, K.; Yamada, S.; Kaneda, T.; Itami, K. Chem. Rev. 2017, 117, 9302−9332. (g) Park, Y.; Kim, Y.; Chang, S. Chem. Rev. 2017, 117, 9247−9301. (h) Wei, Y.; Hu, P.; Zhang, M.; Su, W. Chem. Rev. 2017, 117, 8864−8907. (i) Yang, Y.; Lan, J.; You, J. Chem. Rev. 2017, 117, 8787−8863. (9) For reviews on asymmetric C−H functionalization, see: (a) Giri, R.; Shi, B.-F.; Engle, K. M.; Maugel, N.; Yu, J.-Q. Chem. Soc. Rev. 2009, 38, 3242−3272. (b) Wencel-Delord, J.; Colobert, F. Chem. - Eur. J. 2013, 19, 14010−14017. (c) Zheng, C.; You, S.-L. RSC Adv. 2014, 4, 6173−6214. (d) Gao, D.-W., Zheng, J., Ye, K.-Y., Zheng, C., You, S.-L. In Asymmetric Functionalization of C−H Bonds; You, S.-L., Ed.; Royal Society of Chemistry: Cambridge, U.K., 2015; p 141. (e) Newton, C. G.; Wang, S.-G.; Oliveira, C. C.; Cramer, N. Chem. Rev. 2017, 117, 8908−8976. (10) For enantioselective synthesis of heterocycles via Pd(0)catalyzed C−H arylations, see: (a) Anas, S.; Cordi, A.; Kagan, H. B. Chem. Commun. 2011, 47, 11483−11485. (b) Nakanishi, M.; Katayev, D.; Besnard, C.; Kündig, E. P. Angew. Chem., Int. Ed. 2011, 50, 7438− 7420
DOI: 10.1021/acscatal.7b02783 ACS Catal. 2017, 7, 7417−7420
