Ring contraction of hydroporphinoid to corrinoid complexes.

Crystalline nickel(II) and dicyanocobalt(III) complexes of a racemic 1,2,2,7,7,12,12,17,17,20-decamethyl-20-hydroxy-1,2,3,7,8,12,13,20-octahydro- 17H-porphyrin rearrange to the corresponding complexes of racemic 19-acetyl-1,2,2,7,7,12,12,17,17-nonamethyl-trans-corrin on melting (approximately 290 degrees C and 260 degrees C, respectively). The nickel(II) 19-acetylcorrinate formed in this way is shown to deacetylate to racemic nickel(II) 1,2,2,7,7,12,12,17,17-nonamethyl-trans-corrinate on treatment with 2 M KOH. These reactions are being studied as potentially biomimetic chemical models for the elusive ring contraction step in vitamin B(12) biosynthesis.