Pyrroles and related compounds. Part XII. Stepwise synthesis of porphyrins through a-oxo-bilanes

Abstract

Stable crystalline dibenzyl a-oxobilane-1′,8′-dicarboxylates have been prepared from 5-benzyloxycarbonyl-5′-chloromethylpyrroketones and 5′-benzyloxycarbonylpyrromethane-5-carboxylic acids. The internuclear carbonyl group can be removed by reduction with diborane, and then hydrogenolysis of the benzyloxycarbonyl groups and dehydrogenation with t-butyl hypochlorite leads to b-bilene-1′,8′-dicarboxylic acids, which are cyclised with methyl orthoformate and trichloroacetic acid and aerially oxidised to porphyrins. The examples of mesoporphyrin IX dimethyl ester, 4-ethyl-6,7-dimethoxycarbonylethyl-1,2,3,5,8-pentamethyl-porphin, and 2-ethyl-6,7-dimethoxycarbonylethyl-1,3,4,5,8-pentamethyl-porphin demonstrate that the synthesis is rational.