Research on photochemical and thermochemical reactions between indole and quinones in the absence of solvent

The solid state photochemical reaction of indole with 1,4-naphthoquinone yielded 5H-dinaphtho[2,3-a:2',3'-c]carbazole-6,11,12,17-tetrone (1) in addition to 2-(3-indolyl)-1,4-naphthoquinone (2) which was also the only product in the solution photoreaction. Solventless thermochemical reactions of indole with phenanthrenequinone in the presence or absence of zinc chloride gave 10-(1H-indol-3-yl)-9-phenanthrenol (3) and 9,10-dihydro-9-(1H-indol-3-yl)-10-(3H-indol-3-ylidene)-9-phenanthrenol (4) or 10,10-di-1H-indol-3-yl-9(10H)-phenanthrenone (5), respectively. All of these products were only obtained in trace amount in corresponding solution reactions, and are different from the adduct 10-hydroxy-10-(1H-indol-3-yl)-9(10H)-phenanthrenone (6) obtained in the solution photoreaction. A possible mechanism for formation of 4 and 5 is described in terms of electron pair donor/acceptor complexation.