A New Convergent Method for Porphyrin Synthesis Based on a “3 + 1” Condensation.

A new methodology based on the ‘3 + 1’ acid-catalytic condensation of tripyrranes and pyrrole-2,5-dicarbaldehyde has been used, for the first time, for the synthesis of two types of porphyrins: vic-dipropionic ester porphyrins 30 and 31 including an analogue of the corallistin-A and vic-diacrylic ester porphyrins 32 and 34. For this purpose, synthesis of various tripyrranes and pyrrole-2,5-dicarbaldehydes have been reported and characterized. Studies by dynamic 1H NMR of sterically hindered tripyrranes show conformational exchange, in solution. Structures of the new porphyrins have been confirmed by 1H NMR spectrometry. Introduction of diacrylic ester groups in vicinal positions markedly influences the electronic spectra of compounds 32 and 34 which present an oxorhodo-type absorption pattern.