Benzotriazole-mediated 4-position derivatization of 2,6-diarylpyrylium cations by electrophiles

2,6-Diaryl-4H-(benzotriazolyl)pyrans (7a-c) on treatment with n-butyllithium undergo smooth lithiation at the position α to the benzotriazolyl moiety. In contrast to fused and bridged pyranyl derivatives, these pyranyl anions react with electrophiles by two routes: i) the expected electrophilic substitution resulting in various 4-alkyl- and 4-(ω-alkylfunctionalized)-pyrylium salts (12–19) or ii) pyrylium ring rearrangement of 2,6-diarylpyrylium anions (8a-c), leading to 1,2-diaryl-2,4-cyclopentadien-1-ols (10a-c