Synthesis of chlorophyll- <i>a</i> derivatives conjugated with imidazolium or pyrazolium cations

The oxidative coupling reactions of methyl pyropheophorbide-[Formula: see text], possessing a vinyl group at the 3-position, a chlorophyll-[Formula: see text] derivative, with 1-methyl/phenyl-azapyrroles (1,2/3-diazoles), including imidazoles, pyrazoles, benzimidazoles, and indazoles, by the action of silver(I) hexafluorophosphate and iodine were examined. After stirring in dichloromethane and acetonitrile at room temperature for 3 h, the [Formula: see text]-hydrogen atom of the peripheral 3-vinyl group on the core chlorin [Formula: see text]-system was substituted with some of the positively charged 2/3-(benz)azapyrrol-2/3-ium-2/3-yl (diazolino) groups. The production of the cationic azapyrrole-chlorin adducts under the mild reaction conditions was dependent on the steric effect around the reactive imino nitrogen atom in the azapyrroles.