The first isolation of unsubstituted porphyrinogen and unsubstituted 21-oxaporphyrinogen by the ‘3+1’ approach from 2,5-bis(hydroxymethyl)pyrrole and tripyrrane derivatives

The treatment of 2,5-bis(hydroxymethyl)pyrrole or 2,5-bis(hydroxymethyl)furan with pyrrole in the presence of hydrochloric acid gave tripyrrane and 2,5-bis(2-pyrrolylmethyl)furan in 58–61% yield, which afforded the simplest porphyrinogen (hexahydroporphine) and 21-oxaporphyrinogen by the ‘3+1’ approach in 14 and 11% yields, respectively. 21-Oxaporphyrinogen has been shown to adopt a 1,2-alternated conformation in the solid state by X-ray crystallography.