Ruthenium-catalyzed tandem enyne-cross metathesis–cyclopropanation: three-component access to vinyl cyclopropanes

Substituted vinylcyclopropanes are prepared through a ruthenium-catalyzed, tandem three-component coupling between an olefin, alkyne, and diazoester. Grubbs’ 2nd generation (NHC) ruthenium complexes in the presence of ethylene effect a stereoselective enyne-cross metathesis between alkynes and olefins to generate 1,3-substituted dienes. The slow introduction of diazoacetates to this reaction mixture then allows for the regioselective cyclopropanation of the resulting diene. When the olefin reaction partner is just ethylene (i.e., R′ = H), the tandem process is less efficient. In this case, the byproducts provide unique insight into possible catalyst decomposition pathways.