Ruthenium-Catalyzed Processes:  Dual [2+2] Cycloaddition versus Cyclopropanation of Bicyclic Alkenes with Propargylic Alcohols

Propargylic alcohols have been found to exhibit dual reactivity with bicyclic alkenes in the presence of Cp*Ru(cod)X (X =Cl, Br, I; Cp* = pentamethylcyclopentadienyl, cod = 1,4-cyclooctadiene). Cyclopropane and cyclobutene products can be obtained in a highly stereoselective fashion. but their formation is dependent on a variety of factors including the functional groups attached to the alkyne or alkene moieties and the nature of the ruthenium catalyst. To the best of our knowledge, this cyclopropanation proceeding through a beta-hydride elimination or a [1,2]-hydride shift is an unprecedented catalytic pathway for ruthenium complexes.