Synthesis of 1,4,5,8-tetraethyl-2,3,6,7-tetravinylporphyrin from a Knorr's pyrrole analogue

Abstract

The concise synthesis of symmetric 1,4,5,8-tetraethyl-2,3,6,7-tetravinylporphyrin was developed. The starting material was a close analogue of Knorr's pyrrole prepared from inexpensive commercial β-diketones. The pyrrole was derived into a pair of 3,3′-diacetyl-2,2′-dipyrromethanes. Two precursory dipyrromethanes were coupled to afford tetraacetylporphyrin under the MacDonald condition. The porphyrin was finally converted into a β-tetravinylporphyrin through tetra(1-hydroxyethyl)porphyrin. The structural profile and the utility of the tetravinylporphyrin as the biological prosthetic group and the multiporphyrin scaffold were discussed.