Three benzyl 1-cycloalkenyl ketones, I–III, were irradiated in the presence of borontrifluoride-diethylether (0.05 mol/1) in benzene to give the products V–VII, formed by the bonding between the β-position of αβ-unsaturated ketone and the ortho position of the benzene ring. Benzyl 1-cyclooctenyl ketone (IV) was inactive to the photocyclization because of the preferential geometrical isomerization