Magnesium cyclopropylidenes generated from 1-chlorocyclopropyl phenyl sulfoxides with Grignard reagents: their properties, and a sulfoxide version of the Doering–Moore–Skattebol reaction

Magnesium cyclopropylidenes were generated from 1-chlorocyclopropyl phenyl sulfoxides with Grignard reagents (EtMgCl or i-PrMgCl) in THF at −78°C in high yields by a sulfoxide–magnesium exchange reaction. The generated magnesium cyclopropylidenes were found to be stable at below −60°C for at least 3 h. It was also found that the pyramidal inversion of the magnesium carbenoid was quite slow at below −60°C. When the sulfoxide–magnesium exchange reaction was conducted with phenylmagnesium chloride at 0°C, the 1-chlorocyclopropyl phenyl sulfoxides gave allenes in good to high yields.