Structures and photochemistry of dibenzobarrelene monoamides

The photochemistry of 9,10-ethenoanthracene-11-monoamides has been studied and correlated with the crystal structures determined for two derivatives; photoproduct structures have been established from a crystal structure analysis of one of the products and from NMR correlations. Crystal data are: (1)-Et, N,N-diethyl-9,10-dihydro-9,10-ethenoanthracene-11-carboxamide, C21H21NO, Pbca; (1)-Pr, 9,10-dihydro-N,N-di(isopropyl)-9, 10-ethenoanthracene-11-carboxamide, C23H25NO, P2(1)/c; (2L)-Bz, 9,10-dihydro-9,10-ethenoanthracene-11-spiro-3’-(1-benzyl-4-phenylazetidi ne)-2’-one, C31H25NO (+ solvent), P2(1)/a (Z = 8). The two dibenzobarrelene molecules have geometries and dimensions similar to those of related materials; the amide group in each molecule is only partially conjugated with the C11=C12 double bond. Mechanism are derived for the formation of three types of photoproduct: (i) the well known di-pi-methane reaction [(2M)-type photoproduct]; (ii) a hydrogen abstraction process (2H); (iii) beta-lactam formation (2L).