Constructing QuaternaryCenters of Chirality: The Lanthanide Way to Trifluoromethyl-SubstitutedTertiary Alcohols

Enantiomerically enriched trifluoromethyl-substituted alcoholshaving a quaternary center of chirality can be prepared by the catalyticenantioselective addition of carbon nucleophiles to trifluoromethylketones, trifluoropyruvates, or the like. In particular, chirallanthanide(III) salt complexes of 3,3′-bis[(diethylamino)--methyl-]-1,1′-binaphthalene-2,2′-diol(Binolam) were examined as catalysts for the enantioselective additionof nitromethane to alkyl, aryl, or alkynyl trifluoromethyl ketones.The corresponding nitro-aldols were obtained in moderatechemical yields and good enantio-selectivities. The absoluteconfiguration of the product was determined to be S whenthe lanthanum complex (Δ ,S,S,S)-[(Binolam-) 3 La(OTf) 3 ] wasused as a catalyst (25 mol%) in the presence of an equivalentamount of 1,8-bis(dimethylamino)naphthalene in anhydrous acetonitrile.The nitroaldol adducts were reduced to the corresponding amino alcoholsby nickel boride (nickel chlor-ide/sodium tetrahydroborate)in methanol.