Carbonyl Propargylation from the Alcohol or Aldehyde Oxidation Level Employing 1,3‐Enynes as Surrogates to Preformed Allenylmetal Reagents: A Ruthenium‐Catalyzed CC Bond‐Forming Transfer Hydrogenation

Transcending oxidation level: Under the conditions of ruthenium-catalyzed transfer hydrogenation, conjugated enynes couple to benzylic, allylic, and aliphatic alcohols or aldehydes to furnish products of carbonyl propargylation (see scheme; dppf=1,1′-bis(diphenylphosphino)ferrocene, TBS=tert-butyldimethylsilyl). Isotopic labeling studies corroborate a mechanism involving hydrogen donation from the alcohol to the enyne.