Linear Free Energy Analysis on the Ring‐Expansion of Arylthiiranes with Ketenes

Abstract

The ring‐expansion of arylthiiranes and phenoxyacetyl chloride was performed in the presence of triethylamine and provided a novel strategy for the synthesis of 4,5‐dihydrobenzo[d]thiepin‐2(1H)‐ones, benzo[d]‐ϵ‐thiolactones, directly without catalysts or additives. Its linear free energy analysis was conducted on the basis of competitive experiments. The results indicate that both reaction constants are close to zero (0.14 for σm and 0.20 for σp), supporting the proposed sulfur‐shifted ene mechanism. The current reaction features atom and step‐economic one‐pot characteristic via a tandem sequence of in situ ketene generation, sulfur‐shifted ene reaction, and aromatization.