Protonation and Alkylation of Cross-conjugated Ketones Containing a Terminal N-Methylpyrrole Ring

The protonation and alkylation of cross-conjugated ketones containing a terminal N-methylpyrrole ring takes place at the oxygen atom. Protonation is accompanied by a strong bathochromic shift of the absorption maximum in the electron spectrum, while alkylation leads to ethoxypolymethine salts. The possibility of using these salts for the synthesis of ethoxycyanine dyes was studied.