Electronic effects of ring substituents on triplet benzylic biradicals.

[reaction: see text] UV irradiation of alpha-(o-alkylphenyl)acetophenones with a methoxy or cyano substituent para to the o-alkyl group of the alpha-aryl ring has revealed that a methoxy group slightly increases the stereoselectivity but not the quantum yield of indanol formation, whereas a cyano group greatly lowers both diastereoselectivity and quantum efficiency, confirming the likelihood that hydrogen-bonding of the hydroxy group to the alpha-phenyl ring plays an important role in the cyclization of the photogenerated triplet 1,5-biradical intermediates.