INTRAMOLECULAR HYDROGEN-BONDING IN SYMMETRICAL DIPYRRYLMETHANES

Symmetric dipyrrylmethanes were prepared by converting ethyl 5-methylp yrrole-2-carboxylates into corresponding 5-methyl substituted pyrroles oxidized by bromine, and then self-condensed without separation and p urification. The N-H H-1 NMR analysis and molecular conformation compu tation revealed that strong intramolecular hydrogen bondings exist in dipyrrylmethane 2b and 2e (3,3' substituents are formate and acetate e sters), while very weak or no intramolecular hydrogen bonding exist in other dipyrrylmethanes.