Enantioselective organocatalytic addition of oxazolones to 1,1-bis(phenylsulfonyl)ethylene: A convenient asymmetric synthesis of quaternary α-amino acids

A new, easy, and highly enantioselective method for the synthesis of quaternary α-alkyl-α-amino acids based on organocatalysis is reported. The addition of oxazolones to 1, 1-bis(phenylsulfonyl)ethylene is efficiently catalyzed by simple chiral bases or thioureas. The reaction affords α-disubstituted α-amino acid derivatives with complete C4 regioselectivity and with excellent yields and enantioselectivities. This methodology is complementary to previously reported enantioselec-tive approaches to quaternary ot-amino acids and allows the synthesis of αphenyl-α- alkyl-α-amino acids and αiert-butyl-α-alky1-α-amino acids. It has distinct advantages in terms of operational simplicity, enviromentally friendly conditions, and suitability for largescale reactions.