α-Ketoacid Intermolecular Hydrogen Bonding. Supramolecular Ribbons and Stacking in α-Pyrroleglyoxylic Acids

Rarely-seen carboxylic acid to ketone intermolecular hydrogen bonding is found in crystal structures of α-pyrroleglyoxylic acids. 3,4-Diethyl-1H-pyrrole-2-glyoxylic acid, prepared by saponfication of the reaction product between 3,4-diethylpyrrole and ethyl oxalyl chloride formed crystals that showed the uncommon carboxyl to ketone intermolecular hydrogen bonding, with the hydrogen-bonded α-pyrroleglyoxylic acids stacked neatly in layers. This α-ketoacid hydrogen-bonding pattern was repeated in (Z)-2,3,7,8-tetraethyl-10H-dipyrrin-1-one-9-glyoxylic acid, which also engaged in dipyrrinone-to-dipyrrinone intermolecular hydrogen bonding to form supramolecular ribbons in the crystal.