The Production of Cyclopropanes from Organosulfur Compounds and a Novel Cyclopropane Ring Expansion

The synthetic utility of the remarkable chemical properties of sulfur(II) is illustrated by several of the sulfur-based cyclopropane syntheses that have been developed in our laboratory. A newer method utilizes carbanions generated by aromatic radical-anion induced reductive lithiation of molecules bearing the phenylthio group. This very general carbanion preparation has the unusual feature that the ease of producing the carbanion is inversely correlated with its stability. Examples of this remarkable selectivity are provided. A novel diradical double ring expansion of fused bicyclic allylidenecyclopropanes derived from some of the products is also discussed.