Preparation of α-amino acids via Ni-catalyzed reductive vinylation and arylation of α-pivaloyloxy glycine |
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| Authors: | Xianghua Tao Yanchi Chen Jiandong Guo Xiaotai Wang Hegui Gong |
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| Institution: | College of Materials Science and Engineering, Center for Supramolecular Materials and Catalysis, Department of Chemistry, Shanghai University, 99 Shang-Da Road, Shanghai 200444 China.; Hoffmann Institute of Advanced Materials, Shenzhen Polytechnic, 7098 Liuxian Boulevard, Nanshan District, Shenzhen 518055 P. R. China ; Department of Chemistry, University of Colorado Denver, Campus Box 194, P. O. Box 173364, Denver Colorado 80217-3364 USA, |
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| Abstract: | This work emphasizes easy access to α-vinyl and aryl amino acids via Ni-catalyzed cross-electrophile coupling of bench-stable N-carbonyl-protected α-pivaloyloxy glycine with vinyl/aryl halides and triflates. The protocol permits the synthesis of α-amino acids bearing hindered branched vinyl groups, which remains a challenge using the current methods. On the basis of experimental and DFT studies, simultaneous addition of glycine α-carbon (Gly) radicals to Ni(0) and Ar–Ni(ii) may occur, with the former being more favored where oxidative addition of a C(sp2) electrophile to the resultant Gly–Ni(i) intermediate gives a key Gly–Ni(iii)–Ar intermediate. The auxiliary chelation of the N-carbonyl oxygen to the Ni center appears to be crucial to stabilize the Gly–Ni(i) intermediate.We have developed Ni-catalyzed reductive coupling of N-carbonyl protected α-pivaloyloxy glycine with Csp2-electrophiles that enabled facile preparation of α-amino acids, including those bearing hindered branched vinyl groups. |
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