Pyrylium salt formation from aromatic ketones. Part I. Reactions of β-methylchalcones in non-aqueous acidic media

Abstract

Acetic acid solutions of 4,4′-disubstituted β-methylchalcones (substituents H, Me, MeO, Cl, or F) react in the presence of Lewis acids (SnCl₄, ZnCl₂, or SbCl₃) and benzoyl chloride to give the corresponding bis-2-methyl-4,6-diarylpyrylium MX_{n+ 2}^2– salts, but in the absence of benzoyl chloride bis-2,4,6-triarylpyrylium MX_{n+ 2}^2– salts are formed. The results support the accepted mechanism for the former type of reaction; a mechanism is proposed for the latter. Anomalous anions are formed when the substituent is the methoxy-group.