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 5 H ‐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‐(1 H ‐indol‐3‐yl)‐9‐phenanfhrenol ( 3 ) and 9,10‐dihydro‐9‐(1 H ‐indol‐3‐yl)‐10‐(3 H ‐indol‐3‐ylidene)‐9‐phenanthrenol ( 4 ) or 10,10‐di‐1 H ‐indol‐3‐yl‐9(10 H )‐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‐(1 H ‐indol‐3‐yl)‐9(10 H )‐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.