Catalytic Asymmetric Synthesis of Aminophosphonic Acids Directed toward Peptide Mimetics

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The catalytic and enantioselective hydrophosphonylation of cyclic imines has achieved for the first time. In addition, we have uncovered a new and highly efficient asymmetric approach to cyclic-amino phosphonates using thiazolines as the imine model component. The desired pharmaceutically interesting phosphonates could be synthesized by a heterobimetallic (R)-LnPB-catalyzed (Ln=lanthanoid metal, P=potassium, B=(R)=binaphthol) hydrophosphonylation of the C=N double bond with up to 98% enantiomeric excess and up to 98% chemical yield. A detailed investigation concerning the dependence of enantioselectivity and chemical yield, respectively, on a series of reaction parameters (e.g., lanthanoid and alkali metal, splvent, reaction temperature, pressure, and catalytic amount) is reported. An optimized catalytic lanthanoid system "(R)-YbPB(5 mol %) / 50ﾟC / 48 h / THF-toluene (1 : 7)" was found. The catalytically active complex was isolated and analyzed by spectroscopic methods. In addition, ^<32>P and ^1H NMR spectroscopic and LDI-TOF mass spectrometric investigations were carried out to support a postulated mechanistic course for this (R)-LnPB-complex-catalyzed hydrophosphonylation reaction.