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

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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.

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