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.

Multinuclear ('H, "C, lI9Sn) NMR data are presented for a series of compounds of the type XMe,SnCHRCHRCO,Me (X = Me, C1; R, R' = Me, Ph). Values of 'J(H, H), 'J(Sn, H) and 'J(S0, C) were used to assign the preferred conformations of these compounds and at the same time to test the empirical relationships proposed previously for 'J(Sn, C) and (indirectly) 'J(Sn, H); the validity of these relationsbips was confirmed.

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The kinetics of the reactions of 2,4‐dinitrofluorobenzene (DNFB) and 2,4‐dinitrochlorobenzene (DNClB) with 2‐guanidinobenzimidazole (2‐GB) at 40 ± 0.2 °C in dimethylsulphoxide (DMSO), toluene, and in toluene–DMSO mixtures, and with 1‐(2‐aminoethyl)piperidine (2‐AEPip) and N‐(3‐aminopropyl)morpholine (3‐APMo) in toluene at 25 ± 0.2 °C were studied under pseudo first‐order conditions. For the reactions of 2‐GB carried out in pure DMSO, the second‐order rate coefficients were independent of the amine concentration. In contrast, the reactions of 2‐GB with DNFB in toluene, showed a kinetic behaviour consistent with a base‐catalysed decomposition of the zwitterionic intermediate. These results suggest an intramolecular H‐bonding of 2‐GB in toluene, which is not present in DMSO. To confirm this interpretation the reactions were studied in DMSO–toluene mixtures. Small amounts of DMSO produce significant increase in rate that is not expected on the basis of the classical effect of a dipolar aprotic medium; the effect is consistent with the formation of a nucleophile/co‐solvent mixed aggregate. For the reactions of 3‐APMo with both substrates in toluene, the second‐order rate coefficients, kA, show a linear dependence on the [amine]. 3‐APMo is able to form a six‐membered ring by an intramolecular H‐bond which prevents the formation of self‐aggregates. In contrast, a third order was observed in the reactions with 2‐AEPip: these results can be interpreted as a H‐bonded homo‐aggregate of the amine acting as a better nucleophile than the monomer. Most of these results can be well explained within the frame of the ‘dimer nucleophile’ mechanism. Copyright © 2010 John Wiley & Sons, Ltd.

Reactions of strong bases with P-triphenylstannyl substituted propionitriles give high yields of alkenes under mild conditions through, probably, an E l cB mechanism; under the same reaction conditions, p-trialkylstannyl substituted propionitriles give substantially lower yields of elimination products.