Asymmetric Catalysis by Vitamin B12: The isomerization of achiral cyclopropanes to optically active olefins

Achiral spiroactivated cyclopropanes are isomerized to optically active (R)-(cycloalk-2-enyl)-Meldrum's acids ( = (R)-5-(cycloalk-2-enyl)-2,2-dimethyl-1,3-dioxane-4,6-diones) in high yield and ee's up to 86% by catalytic amounts of cob(I)alamin in polar protic solvents.