Norrish type II photoreactivity of β-anisylalkanophenones and solvent effects on stereoselective Yang cyclization

Abstract

In contary to the general notion that β-arylpropiophenones are photostable, photolysis of β-anisylketones 1 and 2 is found to result in Norrish Type II reactions; Yang cyclization affords two cyclobutanols in moderate yields (31-43%) in a highly stereoselective manner. The solvents are found to exert a dramatic influence on the relative ratios of the cyclobutanols in that the major product in a nonpolar solvent such as benzene becomes the minor one in a polar solvent such as acetonitrile or methanol. Photoexcitation of β-anisylalkanophenones leads to Norrish Type II reactions to afford cyclobutanols CB1 and CB2 stereoselectively in moderate yields (31-43%). The composition of the cyclobutanols is dramatically influenced by solvent.