A new convergent method for porphyrin synthesis based on a ‘3 + 1’ condensation

Abstract

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.