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

Andrea-Nekane R Alba, Xavier Companyó, Guillem Valero, Albert Moyano, Ramon Rios

Index: Chemistry 16(18) , 5354-61, (2010)

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Abstract

A new, easy, and highly enantioselective method for the synthesis of quaternary alpha-alkyl-alpha-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 alpha,alpha-disubstituted alpha-amino acid derivatives with complete C4 regioselectivity and with excellent yields and enantioselectivities. This methodology is complementary to previously reported enantioselective approaches to quaternary alpha-amino acids and allows the synthesis of alpha-phenyl-alpha-alkyl-alpha-amino acids and alpha-tert-butyl-alpha-alkyl-alpha-amino acids. It has distinct advantages in terms of operational simplicity, enviromentally friendly conditions, and suitability for large-scale reactions.