Photochemical Reactions of Aromatic Compounds. XXXIII. Photoreactions of 1-Cyanonaphthalene with Indene in Various Solvents

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Abstract
The stereospecific photocycloaddition of 1-cyanonaphthalene to indene occured in cyclohexane, benzene, diethyl ether, tetrahydrofuran, and ethyl acetate, giving the endo head-to-head cycloadduct as the sole 1:1-adduct. The mechanism was discussed in terms of the exciplex intermediacy. In methanol or in acetonitrile in the presence of water, the photoreaction gave the dihydrocycloadduct (8), accompanied by the formation of 2-methoxyindan and 2,2′-dimethoxy-1,1′-biindanyl or 2-indanol and 1-hydroxy-2,2′-biindanyl. In these solvents, the reactions were suggested to be initiated by photochemical electron transfer; the methoxylated or hydroxylated compounds are formed by the nucleophilic attack of methanol or water on the indene cation. Anionic species, including the 1-cyanonaphthalene anion, were suggested to play important roles in the formation of 8.