Carboxyl-modified amino acids and peptides: I) An efficient method for the synthesis of monofunctionalized enamines and monofunctionalized methyl ketone derivatives from thioamides via episulfides and thioiminium salts

Abstract

Thioamides 4 were transformed by two convenient routes to various functionalized enamines 7 containing different electron-withdrawing groups E which on subsequent hydrolysis gave the corresponding methyl ketone derivatives 8. Application of this methodology to obtain modified dipeptides at the carboxyl end, the determination of stereochemistry and the degree of racemization are discussed.