meso-Substituted Dipyrromethanes from Vinylogous Aromatic Heterocycles and Their Utilization to the Synthesis of meso-Functionalized Porphyrins

摘要

meso-Functionalized dipyrromethanes 6-10 were synthesized by acid-catalyzed addition of pyrrole to exposition of 2-alkenyl pyrroles.The regiochemistry of the reaction can be explained by either the formation of more stable carbocation intermediate or beta-addition of alpha,beta-unsaturated carbonyl compounds.The starting 2-alkenyl pyrroles were synthesized by Aldol condensation of 2-formylpyrrole with active methylene compounds such as nitromethane,diethylmalonate and malononitrile.Attempted '2+2'condensation of meso-diethyl-malonyldipyrromethane,meso-(p-tolyl)dipyrromethane and p-tolualdehyde afforded three different porphyrins 12,13 and 14 in reasonable yields.On the other hand,meso-(nitromethyl)dipyrrornethane with p-(t-butyl)benzaldehyde resulted in the formation of three different porphyrins such as 5,15-dicyano-10.20-diarylporphyrin(16),5-cyano-15-formyl-10,20-diarylporphyrin(17)and 5,15-diformyl-10,20-diarylporphyrin(18)in low yields.Conversion of nitromethyl groups to nitrile and(or)formyl group was observed under the porphyrin forming conditions.