Synthesis of some new α,α-dioxoketene-N,S- and -N,N-acetals derived from secondary aliphatic amines

Abstract

A total of 11 new α,α-dioxoketene- N,S -acetals (2a–2k) and two new α,α-dioxoketene- N,N -acetals (3j and 3k) have been synthesised by treating 3-[bis(methylthiol)methylene]pentane-2,4-dione (1) with increasing mole ratios of secondary aliphatic amines at room temperature, in either toluene or ethanol. Eight non-cyclic N -methylalkyl and N -ethylalkyl amines and the azacyclopentane of pyrrolidine yielded exclusively mono-substituted N,S -acetals (2a–2i), while the azacyclohexanes of piperidine and morpholine yielded the mono-substituted N,S -acetals 2j and 2k and the double-substituted N,N -acetals 3j and 3k. The conversion yields for the reactions in ethanol are considerably higher than those in toluene. Furthermore, the secondary aliphatic amines with an N -methylalkyl moiety, which have one primary α-carbon and less steric crowding around the nucleophilic nitrogen, appear to be more reactive towards 1 than those with the N -ethylalkyl group, which have two primary α-carbons; further, the latter amines are more reactive than the amines with secondary α-carbons.