Ring contraction of hydroporphinoid to corrinoid complexes

Ring contraction of hydroporphinoid to corrinoid complexes

Vittorio Rasetti*,
Andreas Pfaltz*,
Christoph Kratky†, and
Albert Eschenmoser*

^*Laboratory of Organic Chemistry, Eidgenössische Technische Hochschule Zürich, Universitätstrasse 16, CH-8092 Zürich, Switzerland
^†Institute of Physical Chemistry, University of Graz, Heinrichstrasse 28, A-8010 Graz, Austria

Abstract

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°C and 260°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 B₁₂ biosynthesis.