Catalytic Asymmetric Synthesis of Cyclic Ethers Containing an [alpha]-Tetrasubstituted Stereocenter

'Ether' furan or pyran: The exo-selective cyclization of enantioenriched allenols is accomplished with high chirality transfer using as little as 0.02mol% of a gold catalyst. The new method is effective in the synthesis of a wide range of enantioenriched cyclic ethers, which are prepared in excellent yields in three steps from readily available propargylic phosphates.