Small but Effective: Copper Hydride Catalyzed Synthesis of α‐Hydroxyallenes

Mild and efficient: The copper hydride catalyzed diastereoselective SN2′ reduction of propargyl oxiranes provides α-hydroxyallenes bearing various functional groups (ethers, esters, alcohols; see scheme, PMHS=polymethylhydridosiloxane). The best results were obtained with a copper hydride catalyst and an N-heterocyclic carbene ligand. The resulting allenes are useful substrates, as they undergo, for example, regio- and chemoselective cycloisomerization to give 2,5-dihydrofurans.