Preparation and rearrangement study of novel thiophenium- and selenophenium-ylides

Abstract

A series of the title ylides was prepared by reaction of fused thiophene and selenophene derivatives with di-tert-butyl diazomalonate. Their thermal stability depended highly on their structure. While the terminal thiophenium- and selenophenium-ylides smoothly rearranged to the corresponding thiopyran and selenopyran derivatives, the internal thiophene ylides showed remarkable stability. The latter also exhibited hindered rotation around the S–C ylide bond and a high rotational barrier could be established in an NMR study.