Phototranspositions of alkyl-substituted pyrylium cations. Dependence upon substitution pattern

Abstract

U.v. irradiation of a series of tri-, tetra-, and penta-alkyl-substituted pyrylium perchlorates in acetonitrile resulted in phototransposition only when positions 3 and 5 were both alkyl-substituted; possible mechanisms involving 2,6-bonding are discussed in the light of the dependence upon the substitution pattern and a reinter-pretation of the previously reported photohydrations of pyrylium cations is offered.