Influence of Microemulsions on Enantioselective Synthesis of (<i>R</i>)-Cyclopent-2-enol Catalyzed by Vitamin B₁₂

Abstract

The influence of microemulsions on the vitamin B12-catalyzed enantioselective isomerization of 1,2-epoxycyclopentane (1) to form (R)-cyclopent-2-enol (2) has been examined. The reaction was initiated by a reduction of vitamin B12 to the Co(I) form by Zn/NH4Cl. The largest enantiomeric excess (e.e.) in the products was 52% for (R)-2 obtained in a bicontinuous sodium dodecyl sulfate (SDS) microemulsion. A water-in-oil SDS microemulsion gave a poorer percent e.e. probably because of limited catalyst utilization in the water droplets. The influence of the pH of the water phase, the amount of water, and the concentration of vitamin B12 on the enantioselectivity and yield of the reaction was also explored. Results suggest that factors such as higher water content and bicontinuous fluid structure facilitated efficient intermixing of catalyst with reactant to form a key organocobalt intermediate, thus improving enantioselectivity.