Binaphthyl biaryls derived from

Generally, the chiral quaternary ammonium salts, derived from cinchona alkaloids [26, 28, 29, 46, 56-60] and C2-symmetric chiral binaphthyl or biaryl structures [61-68, 71-73, 77], were demonstrated to be very enantioselective catalysts for the asymmetric alkylation of 65a, and provided the corresponding chiral a-amino acids in over 95% ee in most cases. The tartaric acid-derived catalysts 48a [81] and 52 [84] and chiral guanidinium salts 53 [85] and 54 [86] were also found to be suitable for this alkylation reaction. However, in terms of catalytic activity, only a... 

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