A New Method for Selective Activation of Amino, Hydroxy, and Mercapto Carboxylic Acids at the Carboxyl Group: Preparation of Thiol and Selenol Esters

Effective new acylating agents, the enol esters (3), are accessible by selective reaction of the ketone (1) with carboxylic acids (2) containing OH, NH2, or SH groups. The stable enol esters (3) (yields >90%) are transformed into thiol esters (4), XS, in good yields on reaction with alkali metal thiolates. Potential applications exist in the synthesis of macrolides and peptides.