The photosensitized triplet reactions of several 1-allyl-substituted indenes have been studied. The tripletsensitized irradiations gave benzotricyclo [3.3. 0.0 z~ 7] octanes in good yield by means of a novel intramolecular [2+ 21 cycloaddition. The effect of substituents on the regioselectivity of the sensitized rearrangement was studied in some detail. With the simple 1-allyl-substituted isomer, 1, 5-cyclization of the excited state is the preferred path. ...