Benzotriazole-mediated conversions of para-H-substituted pyrylium, benzo[b]pyrylium, and xanthylium salts into para-position functionalized derivatives (an indirect electrophilic substitution of electron-deficient heteroaromatics)

4H-Substituted pyrylium 9, benzo[b]pyrylium 15, and xanthylium salts 22 react with benzotriazole to give the corresponding 4H-(benzotriazol-l-yl)pyrans 10, benzo[b]pyrans 16, or xanthenes 23. Novel anion precursors 10, 16, and 23 undergo smooth lithiations at the positions a to the benzotriazol-1-yl function, i.e., at the para-position of the O-heterosycle. Subsequent trapping with different alkyl halides gives intermediates 14, 21, and 25, which are converted by mineral acid into para-functionalized pyrylium 11-13, benzo[b]pyrylium 17-20, and the xanthylium 24 salts in good to excellent yields.