Some photoproducts from the photochemical cycloaddition reactions between acrylonitrile and 1-methyl-, 2-methyl- and 2,6-dimethyl-naphthalenes

Abstract

Some photoadducts formed between 2-methyl-, 1-methyl- and 2,6-dimethyl-naphthalenes and acrylonitrile are described. 2-Methylnaphthalene gives one main product, 2a-methyl-1,2,2a,8b-tetrahydrocyclobuta[a]naphthalene-endo-2-carbonitrile, but on one occasion a second adduct, 1,4-dihydro-3-methyl-1,4-ethanonaphthalene-endo-10-carbonitrile was isolated, the product of 1,4-addition to the naphthalene ring. 1-Methylnaphthalene gives a complex mixture from which two products were isolated, only one 8-methyl-1,2,2a,8b-tetrahydrocyclobuta[a]naphthalene-endo-1-carbonitrile in a pure state. This was formed by addition of acrylonitrile to the unsubstituted ring. The second was a [2 + 2] adduct of acrylonitrile across the 1,2-double bond of the naphthalene. 2,6-Dimethylnaphthalene gives only one product 2a-methyl-1,2,2a,8b-tetrahydrocyclobuta[a]naph-thalene-endo-2-carbonitrile. The regio- and stereo-chemistry of this was proved by a novel method, converting the nitrile into an acid, which readily formed a mixture of γ and δ iodolactones with iodine–hydrogen carbonate.