Asymmetric Synthesis of a-Mercapto-b-Amino Acid Derivatives: Application to the Synthesis of Polysubstituted Thiomorpholines

Tandem conjugate addition of homochiral lithium N-benzyl-N-(alpha-methyl-p-methoxybenzyl)amide to tert-butyl cinnamate and enolate trapping with (TsSBu)-Bu-t proceeds with high diastercoselectivity to give a homochiral anti-alpha-tert-butylthio-beta-amino ester. Stepwise deprotection gives the corresponding free alpha-tert-butylthio-beta-amino acid without epimerisation. Tandem conjugate addition of homochiral lithium N-allyl-N-(alpha-methylbenzyl)amide to tert-butyl cinnamate and enolate trapping with TsS'Bu followed by conversion of the S-tert-butyl group to a disulphide, and reduction with Lalancette's reagent generates polysubstituted thiomorpholine derivatives. (c) 2006 Elsevier Ltd. All rights reserved.