Stereoselective cyanosilylation of α-sulfinylketimines or its covalently stabilized enamine tautomers.: Synthesis of enantiomerically pure α-sulfinylmethyl-α-amino nitriles

alpha-Sulfinylketimmes and beta-sulfinylenamines undergo reaction with delivery cyanide reagents such as TMSCN or TBDMSCN in the presence of either stoichiometric excesses of ZnCl2 or ZnBr2, or catalytic amount of Yb(TfO)(3). The use of ZnCl2 in alcohol solvents provides the best diastercoselectivity. It is mediated by a chelated transition state, the p-tolyl group driving the anti attack of the reagent. By using Yb(TfO)(3) poor diastereoselectivities but good yields are obtained. It seems that an iminium derivative originated by metal coordination with either the nitrogen or oxygen atom in the substrate is responsible for the observed results. Interestingly, beta-sulfinylenamines provide analogous a-amino nitriles in the same reaction conditions. It allowed the cyanosilylation of the covalently stabilized enamines arising from unstable beta-sulfinyl aldehydes. (C) 2002 Elsevier Science Ltd. All rights reserved.