[2+2]-Photocycloaddition of 2-Morpholinopropenenitrile to Monosubstituted Benzils

Summary.

Triplet excited unsymmetrically substituted benzils react with 2-morpholinopropenenitrile to form oxetanes. Whereas the selectivity with respect to the site of addition (benzoyl vs. 4-substituted benzoyl) is generally low, the photoadditions observed are all unidirectional (“regioselective”) and of high stereoselectivity, as had also been found earlier for benzil itself and for symmetrically 4,4′-disubstituted benzils. The relative configurations of two oxetanes have been unambiguously confirmed by single crystal X-ray structure determinations.