Asymmetric Nitrocyclopropanation of α-Substituted α,β-Enals Catalyzed by Diphenylprolinol Silyl Ether for the Construction of All-Carbon Quaternary Stereogenic Centers
The diphenylprolinolsilylether mediated asymmetricnitrocyclopropanation of α-substitutedα,β-unsaturated aldehydes with bromonitromethane, followed by base-promoted isomerization was found to afford trans-nitrocyclopropanecarbaldehydes with all-carbonquaternarystereogeniccenters with excellent diastereo- and enantioselectivities. DFT calculations indicated that the s-trans conformer of the iminium