Condensation of dipyrromethane with 2-formyl-5-methylpyrrole yields, 1 ,I 9-dimethyl-1 ,I 9-dideoxybiladiene-ac dihydrobromide, which can be cyclised in the presence of nickel or cobalt ions to give the corresponding metal 1 ,I 9-dimethyltetradehydrocorrin salts. Hydrogenation of these salts under a wide variety of experimental conditions gives a mixture of the metal 1 ,I 9-dimethyl-corrin and -4.5-dihydrocorrin salts, which have been separated and isolated as the perchlorates. The corrin has also been isolated as the neutral dicyanocobalt(iri) complex.
BNI 9QJTHE demonstration that the biosynthesis of vitamin B,, depends on porphobilinogen (I) led us to investigate the synthesis of the corrin ring system (11), which as a cobalt (111) complex represents the chromophore of vitamin B,,, based on pyrrolic intermediates. We have reported that the hydrogenation of nickel(I1) 8,12-diethyl-l,3,7,13,17,19-hexamethyltetradehydrocorrin chloride (111; R = H, X = C1) or nickel(I1) 1,7,8,12,-13,19-hexamethyltetradehydrocorrin perchlorate at 160" under 100 atm of hydrogen in the presence of freshly prepared Raney nickel (grade W2) gave the corresponding nickel(11) corrin perchlorates, but these were obtained only as amorphous solids. The failure to obtain crystalline corrins in this way was ascribed to the number of isomers theoretically present, consequent on the several new asymmetric centres created during the hydrogenation. When the chloride (111; R = Me, X = C1) was hydrogenated at 100" under 100 atm of hydrogen, a product was obtained and isolated as the crystalline perchlorate. This was originally formulated as a nickel(r1) monodehydrocorrin salt (IV), i.e. containing seven conjugated double bonds, although this structure is now known to be incorrect and the product will be reformulated as an isomer of the nickel(I1) corrin salt in a forthcoming paper. The difference in the courses of the two hydrogenations was ascribed to steric hindrance between the alkyl groups at C-1, C-2, C-18, and C-19.
