Rapid assembly of polycyclic substances by a multicomponent cascade (4 + 2)-(2 + 2) cycloadditions: total synthesis of the proposed structure of paesslerin A.

A versatile method for stereoselective formation of multisubstituted bicyclo[4.2.0]octane framework has been developed by means of catalytic (4 + 2)-(2 + 2) cycloaddition reactions. Its application to the synthesis of a substance reported to be the cytotoxic sesquiterpene, paesslerin A, is described, and it has been made clear that a revision of the structure of natural paesslerin A is required.