Y. Suga et al., No scrambling in the synthesis of meso-substituted porphyrins from one dipyrromethane and aryl aldehydes, J CHEM R-S, (11), 2000, pp. 512-514
The cross-condensation of dipyrromethane 1 and aryl aldehydes in the presen
ce of trichloroacetic acid in CH2 Cl-2 afforded non-scrambled products in g
ood yields for the first time.