2-Benzopyrylium salts. 39. Recyclization of 2-benzopyrylium salts upon reaction with vinyl ethyl ether and compounds with an active methylene group

The reaction of 2-benzopyrylium salts with vinyl ethyl ether, ethyl acetoacetate, malonodinitrile, and nitromethane gives variously substituted naphthalene derivatives. It is proposed that the reaction with vinyl ether proceeds through 4+2] cycloaddition, while the reaction with the compounds with an active methylene group proceeds either through the ANRORC mechanism or through the formation of bridged intermediates, depending on the conditions.For Communication 38, see 1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 315–320, March, 1990.