A STUDY OF PHOTOADDITION REACTIONS OF CHROMONE

Photoaddition reactions of chromone with different olefins and an acetylene have been carried out and the products identified. Photostability studies have shown that all of the 1:1 adducts are primary photoproducts. Competition experiments indicate that excited chromone is electrophilic in its reaction with extramolecular multiple bonds. Phosphorescence emission data indicates that the n →π* triplet state of chromone is involved in these reactions. This is supported by additional chemical evidence. The photoaddition reaction of chromone with 1,1-dimethoxyethylene indicates that orientational specificity can operate in these reactions. The mechanism of these reactions is probably best described as an electrophilic attack by Cα of the n →π* chromone triplet on the olefin to give a 1,4-diradical intermediate which closes to a cyclobutane. Products derived from initial hydrogen abstraction from the olefin by the carbonyl oxygen of excited chromone are also obtained. © 1969, American Chemical Society. All rights reserved.