Reactions of O-silyl selenocarboxylates; IR and NMR spectra of heteroatom-substituted selenocarboxylates

Abstract

O-Silyl selenocarboxylates 1 react readily with acyl chlorides to give selenoanhydrides. Attempts to synthesize unsymmetrical selenoanhydrides selectively gave mixtures of the desired products with symmetrical selenoanhydrides. Ph₃GeCl, Ph₃SnCl, Ph₃PbCl, Ph₂PCl and Ph₂AsCl were treated with 1 to give the corresponding selenocarboxylates containing a Se–heteroatom bond. Reactions with ArSCI, PhSeBr and PhTel afforded the corresponding arenechalcogenyl selenocarboxylates. The CO stretch of these derivatives showed a shift to lower frequency in moving from lighter to heavier atoms within a group of the Periodic Table. This may partly be due to the delocalization of an electron lone pair on selenium to form a diene type of conjugated system involving the CO and Se–heteroatom bonds. A downfield shift in the signals in the ⁷⁷Se NMR spectra was observed in going from group 14 to group 16 elements; in contrast, the ¹³C NMR signals of the CO moiety were almost independent of the heteroatom attached to Se.