A Polymer-Bound Oxazaborolidine Catalyst: Enantioselective Borane Reductions of Ketones
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文摘
A polymer-bound oxazaborolidine catalyst has been prepared and used in the enantioselective borane reduction of two model ketones. The catalyst is derived from (S)-a,a-diphenyl-2-pyrrolidinemethanol and poly-p-styrene boronic acid (1 % cross-linked). After reduction of acetophenone, the reaction mixture was quenched and the polymer-bound catalyst was recovered by simple filtration. Subsequent use of this catalyst “as is” for a second reduction of acetophenone was investigated and only a marginal loss in selectivity was observed. The selectivity began to diminish during a third and subsequent reductions. The preparation and use of such a polymer-bound catalyst are described.