Factors influencing the regiochemistry of spiro-oxetane formation from the photocycloaddition of ethenes to 1,4-benzoquinone

Abstract

The photoadditions of a variety of electron donor and electron acceptor ethenes to 1,4-benzoquinone have been studied. Spiro-oxetanes were formed in each case, though at markedly varying rates. The reactions were not stereoselective. In all cases except that of isopropenyl acetate, the regiochemistry observed was the opposite of that predicted from the relative stabilities of the two possible intermediate 1,4-diradicals and from the known corresponding photoadditions to ketones and aldehydes. A mechanism involving control of the regioselectivity by polar factors resulting from initial electron transfer to the quinone is proposed.