Base-catalyzed direct conversion of dipyrromethanes to 1,9-dicarbinols: a [2 + 2] approach for porphyrins

A variant of the MacDonald approach was devised for the synthesis of porphyrins. A new base-catalyzed one-step synthesis of 1,9-dipyrromethane-dicarbinols was achieved by Friedel-Crafts alkylation of dipyrromethanes using commercially available ethyl glyoxylate solution in toluene. This method avoids the use of acid chlorides, Grignard reagents, borohydride reductions, and acidic conditions. The 2 + 2] condensation of dipyrromethanedicarbinols and dipyrromethanes yielded 5,15-di(ethoxycarbonyl)porphyrins.