PHOTOCHEMISTRY OF DIARYL VICINAL TETRAKETONES AND CHEMISTRY OF INTERMEDIATE (AROYLOXY)ARYLKETENES

Photolysis of diaryl vic-tetraketones results in formation of tricycli c-gamma-lactones 3 and 4 with low quantum but high chemical yield. (Ar oyloxy)arylketenes and carbon monoxide are the initial photochemical p roducts of these photolyses. Subsequent reaction of ketene with ground -state tetraketone results in formation of the observed photoproducts via intermediate beta-lactones. The latter are formed with a high degr ee of stereoselectivity. The failure of a cyclic tetraketone to react is attributed to its inability to undergo the cyclic mechanism propose d for formation of ketenes from tetraketones. Dimesityl and di-tert-bu tyl tetraketones react by a competing intramolecular hydrogen atom tra nsfer mechanism. Dimerization of (benzoyloxy)phenylketene and its reac tions with a number of tetraketones are described.