Photochemical [2+ 2] cycloaddition of enol acetate 10a to cyclohexene led to a 3: 1 mixture of the tetracyclic photoadducts A and B which, through reverse aldol reactions, under mild alkaline conditions produced two compounds: a tetracyclic ketone 13 and a tricyclic diketone 14. Hydrolytic cleavage in methanolic hydrochloric acid of 15 and 16 resulting from irradiation of the enol ether 10b to cyclohexene gave rise to the rearranged tricyclic ...