Equol, a natural estrogenic metabolite from soy isoflavones: convenient preparation and resolution of R- and S-equols and their differing binding and biological activity through estrogen receptors alpha and beta.

A variety of palladium on activated carbon catalysts differing in Pd dispersion, Pd distribution, Pd oxi- dation state, and water content were tested in Heck reactions of aryl bro- mides with olefins. The optimization of the catalyst (structure ± activity relation- ship) and reaction conditions (temper- ature, solvent, base, and Pd loading) allowed Pd/C catalysts with very high activity for Heck reactions of unactivat- ed bromobenzene (turnover number (TON) 18 000, turnover frequency (TOF) up to 9000, Pd concentrations down to 0.005 mol %) to be developed. High Pd dispersion, low degree of re- duction, sufficient content of water, and uniform Pd impregnation are criteria for the most active system. The catalysts combine high activity and selectivity under ambient conditions (air and mois- ture), easy separation (filtration), and quantitative recovery of palladium. De- termination of Pd in solution after and during the reaction, and catalyst charac- terization before and after the reaction (transmission electron microscopy (TEM), X-ray diffraction (XRD)), indi- cate dissolution/reprecipitation of palla- dium during the reaction. The Pd con- centration in solution is highest at the beginning of the reaction and is a mini- mum ( 1 ppm) at the end of the reac- tion. Palladium leaching correlates sig- nificantly with the reaction parameters.

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Highly Active Palladium/Activated Carbon Catalysts for Heck Reactions: Correlation of Activity, Catalyst Properties, and Pd Leaching

Reserpine: A Challenge for Total Synthesis of Natural Products

Parameters that influence the palladium leaching during and after Heck reactions of aryl bromides with olefins catalyzed by heterogeneous Pd on activated carbon systems are reported. Pd leaching correlates significantly with the progress of the reaction, the nature of starting materials and products, solvent, base and atmosphere. The Pd concentration in solution is highest at the beginning of the reaction and is reduced when the reaction is finished. Reaction procedures were developed that allow easy and practicable control and minimization of the Pd leaching at the end of the reaction: Pd re-deposition by: (i) increased temperature, (ii) addition of reducing agents and (iii) working under inert conditions. The Pd concentration in solution after the reaction is reduced to 0.05 ppm Pd (μg Pd/g solution). The catalyst meets all demands for practical application: high activity and selectivity under ambient conditions, complete separation (filtration) of Pd from the product mixture, easy recovery of Pd and commercial availability.

Control of Pd leaching in Heck reactions of bromoarenes catalyzed by Pd supported on activated carbon

New proline derivatives and related compounds which have the general formula ##STR1## are useful as angiotensin converting enzyme inhibitors.

William M. Pearlman

Papers

Noble metal hydroxides on carbon nonpyrophoric dry catalysts