Stereocontrolled Construction of Quaternary Stereocenters by Inter- and Intramolecular Nitro-Michael Additions Catalyzed by Bifunctional Thioureas

A highly diastereo- and enantioselective conjugate addition of beta-keto esters to nitroolefins, catalyzed by a chiral thiourea prepared from l-valine is described. The formation of two contiguous tertiary and quaternary stereocenters occurs in high yield and excellent diastereo- and enantioselection with only 2 mol% of catalyst loading. The reaction is general and different b-keto esters and aryl-and alkylnitroolefins have been tested. The same catalyst has been used to promote the first intramolecular conjugate addition leading to the cyclic adduct in moderate diastereoselectivity and good enantioselectivity.