Benzo[b]thiophenium S,C-ylides: Preparation, structure and comparison with thiophenium analogues

Abstract

A series of new S,C-ylides derived from benzo[b]thiophene and β-dicarbonyldiazocompounds were prepared and characterised. NMR ( 1H, 13C) studies revealed that ylides substituted additionally at position 2 of the thiophene ring can exist as pairs of diastereoisomers, not interchangeable at room temperature. The slow exchange between two sites was attributed to the restricted rotation about the ylidic SC bond. The crystal structure determined for one ylide demonstrated different molecular environment for two parts of the β-dicarbonyl ylidic substituent with respect to the benzothiophene ring. The prepared ylides were found to be much less reactive than the previously studied thiophenium S,C-ylides.