Studies in photochemistry. Part II. The photocyclisation of stilbazoles to azaphenanthrenes

Abstract

Photochemical cyclodehydrogenation of 2-, 3-, and 4-stilbazole in dilute cyclohexane solutions yields benzo[f]quinoline, benz[f]isoquinoline, and benz[h]isoquinoline, respectively. In the case of 3-stilbazole none of the other possible cyclisation product, benzo[h]quinoline, was isolated. Several substituted stilbazole were cyclised; 6-methyl- and α-methyl-2-stilbazole, 4′-methyl- and β-cyano-3-stilbazole, and α-methyl-4-stilbazole yielded the expected 3- and 5-methylbenzo[f]quinolines, 9-methyl- and 6-cyano-benz[f]isoquinoline, and 5-methylbenz[h]isoquinoline, respectively.