Synthesis of corrins and related macrocycles based on pyrrolic intermediates

Intermediate in structure between porphyrins and corrins are the corroles and 1-methyltetradehydrocorrins. These ring systems, like the porphyrins, can be obtained by cyclization of linear tetrapyrrolic compounds, reactions which have been shown to proceed by orbital symmetry-allowed electrocyclic processes, and examples will be quoted. Thermolysis of nickel 1-methyltetradehydrocorrins causes a migration of the methyl group whereas similar treatment of nickel 1,19-dimethyltetradehydrocorrin salts yields porphyrin derivatives; the mechanisms of these transformations have been elucidated. Stepwise hydrogenation of metal tetradehydrocorrin salts (10 double bonds) yields a series of macrocycles containing 9, 8, 7, 6 and 5 double bonds and conditions necessary to obtain corrins have been established.