SYNTHESIS OF FUSED-RING CYCLOBUTENONES VIA A TANDEM [2+2] CYCLOADDITION-BETA-ELIMINATION SEQUENCE

The usual course of the de Mayo reaction involves a base-catalyzed retro-aldol ring fragmentation of initially formed photoadduct 3 to produce medium-sized ring compound 4. It is known that this sequence of events can be altered if the cyclobutane carbon adjacent to the resultant ketone carbonyl of the photoadduct is substituted with a hydrogen atom. Under the basic conditions of the second step, an elimination of the elements of acetic acid to produce cyclobutene derivatives 17 and 18 occurs. The detailed stereochemistry of photoadduct 12, resistant to this elimination, was determined by X-ray crystallography, and further examples of the elimination chemistry are presented to ascertain the scope and limitations of this reaction. The tandem [2 + 2] cycloaddition-beta-elimination sequence provides a straightforward and facile synthesis of cyclobutenone derivatives.