Stereochemical issues on the fragmentation of non-enolisable β-heterosubstituted-cyclopentanones with wet and anhydrous potassium hydroxide

Fragmentation by potassium hydroxide of non-enolisable β-mesyloxy-cyclopentanones fused to a cyclopropane ring in α′,β′-positions proceeds efficiently from derivatives possessing (i) an exo-mesyloxy group and an endo-methyl group on the cyclopropane ring and (ii) an endo-mesyloxy group and an endo-hydrogen on the cyclopropane ring. This reactivity has been tentatively correlated to an antiperiplanar arrangement of atoms and bonds involved in the process accessible from various stereoisomers owing the flexibility of the five-membered ring.