Photochemical behaviour of 9-(2-anilinoethyl)- and 9-(3-anilinopropyl)anthracenes in various solvents

Abstract

Photochemical reactions of the title compounds and related aniline derivatives have been studied in various solvents. Products isolated from an irradiated mixture of 9-(2-anilinoethyl)anthracene (5) were: 9-methylene-9,10-dihydroanthracene (6), N-phenyl-9,10-dihydro-9,10-ethanoiminoanthracene (7), and 9,10-dihydro-9,10-(o-benzeneoiminoethano)anthracene (8). The yield of the main product (8) decreased on changing the solvent from benzene to a polar solvent such as acetonitrile or a benzene–methanol mixture. The yield of compound (6) increased on adding a small quantity of protic solvent such as methanol in benzene. Polar and protic solvents seemed to have no particular influence on the yield of product (7). Similarly, 9-(3-anilinopropyl)anthracene (11) gave, on irradiation in benzene, three isomers of the starting amine (11): N-phenyl-9,10-dihydro-9,10-iminopropanoanthracene (12), 9,10-dihydro-9,10-(o-benzenoiminopropano)anthracene (13), and 1′-phenylspiro[9,10-dihydroanthracene-9,2′-pyrrolidine](14). The yields decreased on adding methanol in solvent. Biradical intermediates were presumed for the reactions of both anthracene derivatives.