Synthesis of nickel 1-alkyltetradehydrocorrins

Nickel 1-alkyltetradehydrocorrins have been prepared by the base-catalysed cyclisation of 19-alkyl-1-bromo-1,19-dideoxybiladiene-ac dihydrobromides in presence of nickel ions. A nickel 1-alkyl-1-deoxybilatriene-abc may be formed as a by-product. The n.m.r. spectra of the nickel 1-alkyltetradehydrocorrins are interpreted and it is also shown that protonation of the neutral metal complexes occurs at the 19-position. The salts undergo smooth deuteriation at the three meso-positions. Conditions for conversion of various 19-alkyl-1-bromo-1,19-dideoxybiladiene-ac dihydrobromides to porphins are also described.