A scalable synthesis of meso-substituted dipyrromethanes

A one-flask synthesis of meso-substituted dipyrromethanes has been refined. The procedure entails reaction of an aldehyde in 100 equiv of pyrrole as the solvent containing a mild Lewis acid (e.g., InCl3) at room temperature. Following removal and recovery of excess pyrrole, the dipyrromethane is obtained by crystallization. The procedure generates minimal waste and does not require aqueous/organic extraction, chromatography, or distillation. The procedure has been scaled linearly to obtain >100 g of 5-phenyldipyrromethane. The utility of various analytical methods for characterizing dipyrromethanes has been investigated.