Efficient synthesis of aryldipyrromethanes in water and their application in the synthesis of corroles and dipyrromethenes

In this paper, we describe the efficient and selective synthesis of aryldipyrromethanes in aqueous medium by acid-catalyzed (HCl) condensations of aromatic aldehydes with 3 equivalents of pyrrole at room temperature. The precipitated aryldipyrromethanes can be isolated directly from the reaction mixture in an essentially pure state by simple filtration. Time control seems to be essential to avoid significant formation of the tripyrromethane analogue and the reaction time is strongly dependent on the nature of the aromatic aldehyde. A one-pot synthesis of several aryldipyrromethenes and various novel meso-aryl-substituted trans-A2B-corroles was also achieved starting from the obtained aryldipyrromethanes. Trichloroacetic acid was the preferred acid catalyst for the preparation of meso-triarylcorroles from the condensation of 5-(2,6-dichlorophenyl)dipyrromethane with more reactive aldehydes, while trifluoroacetic acid was preferred for less reactive substrates.