Highly stereoselective intramolecular α-arylation of self-stabilized non-racemic enolates : synthesis of α-quaternary α-amino acid derivatives

The 'one-pot' stereoselective conversion of N-(4-nitrobenzene)-sulfonyl-alpha-amino acid tert-butyl esters into the corresponding N-alkyl-alpha-(4-nitrophenyl)-alpha-amino esters has been realized through N-alkylation of the starting amido esters, followed by N-C(alpha) migration of the p-nitrophenyl group and the loss of sulfur dioxide; the asymmetric induction is determined by an intermediate non-racemic enolate, without the need of an external source of chirality.