Photochemical reactions of aromatic compounds. Part XXIII. Photochemical reactions of alkyl vinyl ethers with 2-naphthonitrile

Abstract

Irradiation of 2-naphthonitrile (5) and an alkyl vinyl ether (6) at 313 nm gives only a single [2 + 2] cycloadduct, endo-2-alkoxy-1,2,2a,8b-tetrahydrocyclobuta[a]naphthalene-2a-carbonitrile (7), in 80–90% yield. On the other hand, irradiation through Pyrex (>280 nm) ultimately affords a cyclobutene, 4-alkoxy-2a,3,4,8b-tetrahydrocyclobuta[a]naphthalene-6-carbonitrile (8)(70%), as a main product, accompanied by various 1 : 1 adducts (9)–(12). Pyrolyses of the products (8) and (9) afford 10-alkoxy-5,6-dihydrobenzocyclo-octene-2-carbonitrile (10) in good yields; irradiation of (10) gives 8b-alkoxy-2a,3,4,8b-tetrahydrocyclobuta[a]naphthalene-7-carbonitrile (11) in quantitative yield. From a kinetic study, the formation of the adduct (7) is established as occurring from the lowest excited singlet state of the nitrile (5).