Positional Selectivity and Heteroatom Effect in the Reaction of 2,4,6-Triphenylpyrylium and 2,4,6-Triphenylthiopyrylium Ions with Methoxide Ion

Article abstract of DOI:10.1021/jo00345a012

The rate constants for 2H and 4H adduct formation were determined for the reaction of the 2,6-diphenyl-4-X-pyrylium ion (1, X=Ph) and of 2,4,6-triphenylthiopyrylium ion 2 with methoxide ion in methanol solution.The equilibrium constans were evaluated for the formation of the 4H adducts.The ipso attack at the 4-position is found to be in the order H>MeO>Ph for the 4-X substituents and mainly caused by ground-state stabilization for X=Ph.The substrate and positional reactivities of 1 and 2 differ appreciably from each other and suggest that the reaction of 1 and,possibly, 2 are charge rather then orbital controlled.