Synthesis of 3-Benzyl-1,3-thiazolidines by [2+3]-Cycloaddition of sonochemically generated Azomethine Ylides with Thiocarbonyl Compounds

Abstract

Sonification of N-benzyl-N-(methoxymethyl)-N-[(trimethylsilyl)methyl]amine (5a) in the presence of LiF led to the formation of the reactive azomethine ylide 1d, which was intercepted by cyclic thioketones to give spirocyclic 1,3-thiazolidines. In the case of 2,2,4,4-tetramethylcyclobutane-1,3-dithione, the 1:1- and 1:2-cycloadduct, respectively, was formed as the major product depending on the ratio of the starting materials. With 1,3-thiazole-5(4H)-thiones, 1d undergoes stereoselective [2+3]-cycloadditions with the C=S group to yield spirocyclic 1:1-adducts. In the case of the 1,3-dipole generated from N-benzyl-N-(methoxymethyl)-N-[1-(trimethylsilyl)ethyl]amine (5b), the [2+3]-cycloaddition proceeded in a non-regioselective manner leading to a mixture of regio- and diastereoisomers.