Carbonylative, Catalytic Deoxygenation of 2,3-Disubstituted Epoxides with Inversion of Stereochemistry: An Alternative Alkene Isomerization Method

Reactions
facilitating inversion of alkene stereochemistry are rare, sought-after
transformations in the field of modern organic synthesis. Although
a number of isomerization reactions exist, most methods require specific,
highly activated substrates to achieve appreciable conversion without
side product formation. Motivated by stereoinvertive epoxide carbonylation
reactions, we developed a two-step epoxidation/deoxygenation process
that results in overall inversion of alkene stereochemistry. Unlike
most deoxygenation systems, carbon monoxide was used as the terminal
reductant, preventing difficult postreaction separations, given the
gaseous nature of the resulting carbon dioxide byproduct. Various
alkyl-substituted cis- and trans-epoxides can be reduced to trans- and cis-alkenes, respectively, in >99:1 stereospecificity and up to 95%
yield, providing an alternative to traditional, direct isomerization
approaches.