Carboxylic acid to amide hydrogen bonding. 10-Oxo-semirubins

Using their amide (and pyrrole) groups, dipyrrinones act as hydrogen bonding receptors for carboxylic acids, as found in a large number of 10-oxo-semirubins (1-6). The latter can be synthesized readily by Friedel-Crafts coupling of 9-H dipyrrinones with half-ester acid chlorides or diacid dichlorides of α,ω-dicarboxylic acids, ranging from C2 to C10. With ω-oxo-alkanoic acid chains of C5 or ≥C5, intramolecular hydrogen bonding is observed. With acid chains

A series of dipyrrinones (1-6) with varying lengths of ω-oxo-alkanoic acid chains attached to C(9) display hydrogen bonding between the CO2H and dipyrrinone lactam and pyrrole.