syn-anti Diastereoselectivity in the Nicholas reaction via a chiral 1-alkoxy-propargylium cation

The Nicholas reaction between enantiopure propargyl acetal dicobalt–hexacarbonyl complexes, as precursors of chiral propargyl cobalt–hexacarbonyl cations, and several linear and cyclic silyl enol ethers is presented. A high yield up to 95% and high syn-anti diastereoselectivity (from 85:15 up to >99:1) is observed in the generation of the two new stereocenters. Moderate, but promising, syn(R,R)-syn(S,S), up to 70:30, is also observed in this preliminary work.