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Achiral Trisubstituted Thioureas as Secondary Ligands to CuI Catalysts: Direct Catalytic Asymmetric Addition of α-Fluoronitriles to Imines.

Thioureas have emerged as effective hydrogen-bonding catalysts over the last two decades, and they are broadly utilized in asymmetric catalysis. We report that achiral trisubstituted thioureas function as beneficial secondary ligands to CuI catalysts, thereby enabling highly diastereo- and enantioselective addition of α-fluoronitriles to imines. The structure of the thiourea significantly affects the reaction outcome, and kinetic experiments indicate that the thioureas enhance the stereocontrol by binding to the CuI complex. The reaction products can be readily transformed into valuable β-amino acid derivatives bearing a fluorinated tetrasubstituted stereogenic center.