Photochemistry of Diaryl Vicinal Tetraketones and Chemistry of Intermediate (Aroyloxy)arylketenes¹

Abstract

Photolysis of diaryl vic-tetraketones results in formation of tricyclic-gamma-lactones 3 and 4 with low quantum but high chemical yield. (Aroyloxy)arylketenes and carbon monoxide are the initial photochemical products 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 degree of stereoselectivity. The failure of a cyclic tetraketone to react is attributed to its inability to undergo the cyclic mechanism proposed for formation of ketenes from tetraketones. Dimesityl and di-tert-butyl tetraketones react by a competing intramolecular hydrogen atom transfer mechanism. Dimerization of (benzoyloxy)phenylketene and its reactions with a number of tetraketones are described.

The Chemistry of Vicinal Polycarbonyl Compounds

“…Clearly the operation of an equilibrium between polycarbonyl and its hydrate in competition with other processes can lead to much confusion. A simple apparatus has recently been described 106 for obtaining solutions of tetraketones free of traces of water for quantum yield measurements.…”

“…Investigation of the photochemistry (section VI.B) of vic-tetraketones 106 prompted study of the reactions of such tetraketones (2, Ar ) phenyl, p-tolyl, p-anisyl, mesityl, tert-butyl) with (benzoyloxy)phenyl ketene (163). This ketene was generated, in the presence of tetraketone, by reaction of triethylamine and the appropriate R-(aroyloxy)-R-arylcarboxylic acid chloride.…”

“…Photoirradiation of open chain tetraketones 106 provided a delightful contrast to the reactions of tri- (198) or zwitterionic (199)…”