Ultrasound-accelerated synthesis of thioesters through the Ag(I)-catalyzed decarboxylative coupling between α-keto acids and diorganyl disulfides, under mild reaction conditions

Abstract

Here is reported a new, green method to obtain thioesters, using available and ecofriendly starting materials, as -keto acids and an alternative energy source, the ultrasound. The title compounds 3a-3i were prepared in moderate to good yields, through the reaction between glyoxylic acids as acyl transfer agents and diorganyl disulfides, in the presence of AgNO3 as catalyst, K2S2O8 as an oxidant and a mixture of DMSO/H2O as the solvent, in 20 minutes under sonication. In addition, it was performed the chemical modification of chitosan (Cs) 4 with the aim of preparing new biopolymers 6a-6d with improved antifungal and antibacterial properties. The presence of the amine groups in its backbone allows the formation of Schiff bases by reacting them with aldehydes. In this work the aldehyds used were citronellal 5a, citral 5b, -phenylseleno-citronellal 5c and 3-phenylthio- citronellal 5d.