Ring transformations of heterocyclic compounds. XXII. Pyrido[1,2‐a]indolium salts from 2‐methyl‐3H‐indoles by pyrylium mediated three carbon annelation

Abstract The synthesis of pyrido[1,2‐ a ]indolium perchlorates 8,11 from 2,4,6‐triarylpyrylium perchlorates 1 and 2‐methyl‐3 H ‐indoles 6,9 in the presence of a basic condensing agent (anhydrous sodium acetate, piperidine acetate, triethylamine/acetic acid, triethylamine) in ethanol by a 2,4‐[C 3 +C 2 N] pyrylium ring transformation is reported. Spectroscopic data of the transformation products and their mode of formation are discussed.