Two new protected acyl protecting groups for alcoholic hydroxy functions

Abstract

4-(Methylthiomethoxy)butyric acid (13a) and 2-(methylthiomethoxymethyl)benzoic acid (14a) have been prepared in 53 and 64% overall yields from γ-butyrolactone and phthalide, respectively. Thymidine reacts regioselectively with (13a) and (14a), in the presence of an appropriate condensing agent, to give the corresponding 5′-O-acyl derivatives [(20) and (21), respectively], both in 70% yield. The latter compounds undergo deacylation relatively slowly when treated with concentrated aqueous ammonia but, following treatment with mercury(II) perchlorate in the presence of 2,4,6-collidine in slightly wet tetrahydrofuran, are both converted back into thymidine under very mild conditions of basic hydrolysis.