Asymmetric Organocatalytic Addition of Malononitrile to Trifluoromethyl Arylketimines: A Viable Entry to Chiral α-CF3 Quaternary Aminoesters.

In the present study the stereoselective addition of malononitrile to trifluoromethyl arylketimines promoted by chiral iminophosphoranes was investigated. A panel of structurally diverse enantiopure bifunctional superbases, which include thiourea or squaramide unit and a basic site connected by a chiral scaffold, was tested in the asymmetric organocatalytic reaction, to afford an adduct featuring a quaternary stereocenter, in up to a 87/13 enantiomeric ratio. The product was then converted in a single step transformation into the corresponding enantioenriched α-CF3 substituted quaternary aminoester, without any loss of stereochemical integrity. The absolute configuration of the final product was established by chemical correlation of the chiral compound with a known molecule. Preliminary computational studies were performed in order to elucidate the reaction mechanism and rationalize the stereochemical outcome of the reaction.