Synthesis of chiral organotins suitable for the preparation of asymmetric heterogeneous catalysts

A key step in the preparation of asymmetric heterogeneous catalysts based on silica‐supported rhodium and platinum chemically modified with chiral organotins, is the synthesis of optically pure tin derivatives. We report on the synthetic pathways leading to the synthesis of (−)‐menthyltin derivatives without the formation of epimerization by‐products. The physical properties (including full 1 H, 13 C and 119 Sn NMR spectra) of the new compounds, containing between one and three (−)‐menthyl ligands attached to the tin atom, are reported. The preparation of two catalysts based on silica‐supported rhodium and platinum chemically modified with (−)‐menthyldiphenylmethyltin, as well as some studies on the catalytic hydrogenation of ethyl pyruvate, are also described. These studies show that the reductions lead to ( R )‐ and ( S )‐ethyl lactates as the only products, that the ( S ) enantiomer was the isomer formed preferentially, and that the degree of conversion observed using both catalytic systems was almost quantitative (97–100%). The enantiomeric excesses observed were in the range 7–8%. One important advantage of these catalytic systems is their stability. Recycling of the used catalysts is possible, without any loss in the degree of conversion or enantiomeric excess. Copyright © 2005 John Wiley & Sons, Ltd.