Studies on heteroaromaticity. Part XLVIII. Cycloaddition reactions of 4-phenyl-1,2,4-triazoline-3,5-dione with seven-membered ring unsaturated compounds and photochemical behaviour of the adducts

Abstract

Reactions of 4-phenyl-1,2,4-triazoline-3,5-dione (I) with tropone, N-ethoxycarbonylazepine, and N-ethoxycarbonyl-1,2-diazepine give normal (4 + 2)π cycloadducts (VI)—(VIII), respectively, whereas the reaction with tropolone gives the product (IX) of addition across the triazoline double bond. Irradiation of the tropone adduct (VI) in methanol gives two photoisomeric products, (X) and (XI), which are formed by different [3,3]-sigmatropic rearrangements. When heated the N-(phenylcarbamoyl)-1,2-diazepine-N-carboxylates (XI) and (XII) give a novel compound which may be correctly represented as a triaza-annulene structure (XIII), i.e. an aromatic 10 π-electron ring system.