108. Asymmetric Catalysis by Vitamin B,*: The Isomerization of Achiral Cyclopropanes to Optically Active Olefins ... Achiral spiroactivated cyclopropanes are isomerized to optically active (R)-(cycloalk-2-enyl)-Me~drum's ... ( = (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(1)alamin in polar protic solvents. ... Introduction. - Ring opening of cyclopropanes A containing two geminal ...