From chlorocyclobutanones to cage compounds. Strain, proximity effects, and tandem rearrangements

A review of studies in our laboratory on the chemistry of α-chlorocyclobutanones fused to 5-, 6-, and 8-membered rings is presented. The major feature of such compounds is the high propensity to undergo cine substitution with nucleophiles, which is initiated by the intermediacy of oxidoallyl cations. The cine substitution products often undergo interesting transformations which become evident especially when the 4-membered ring is fused to a tetrahydrofuran or a tetrahydropyran. In such cases, beta elimination of the alcohol chain with ring opening of the heterocyclic ring leads to formation of cyclobutenones, which undergo further transformations. Proximity effects as well as strain are responsible for unusual tandem rearrangements and formation of cage compounds.