Concept of improved rigidity: How to make enantioselective hydrophosphonylation of cyclic imines catalyzed by chiral heterobimetallic lanthanoid complexes almost perfect

The catalytic and enantioselective hydrophosphonylation of cyclic imines us ing cyclic phosphites is described for the first time. In contrast to the a pplication of acyclic phosphites, significant improvements are presented ar ising from the concept of improved rigidity by utilization of cyclic phosph ites in the lanthanoid BINOL complex catalyzed hydrophosphonylation of 3-th iazolines. Cyclic phosphites are shown to provide certain improvements with in the catalytic cycle. Influence of parameters such as concentration of th e catalyst and the phosphite on the catalysis is examined as well as the ef fects of the substituents on the starting material. The pharmacologically i nteresting thiazolidinyl phosphonates are synthesized in excellent optical purities of up to 99% ee and high chemical yields of up to 99%. The require d amount of catalyst is reduced to 2.5 mol Sc. The highest efficiency of th e reaction involving cyclic phosphites is achieved using the catalytic syst em "2.5 mol % (S)-YbPB/2.5 equiv phosphite/50 degrees C/48 h/HF-toluene (1: 7)". On the basis of the results a refinement of the proposed catalytic cyc le has been provided. For comparison cyclic phosphites were used in hydroph osphonylation with a chiral titanium catalyst.