Enantioselective Borane Reduction of Ketone

One of the most powerful asymmetric catalytic reductions of ketones is borane reduction with oxazaborolidine catalyst [92, 93]. Various types of polymer-supported chiral amino alcohols have been prepared and used for the formation 

A large number of reducing agents and chiral catalysts have also been developed for the enantioselective reduction of ketones [100]. In the presence of polymer- 

A polyacetylene-type helical polymer having chiral amino alcohol pendant groups has also been prepared by the polymerization of chiral (S )-threonine-based 

Among the various chiral catalysts reported for asymmetric transfer hydrogenation, the most notable has been the ruthenium complex with N-(p-toluenesulfonyl)- 

---

Another soluble polymer-enlarged catalyst was synthesized and tested by Wandrey et a/.[57] The catalyst was prepared by a coupling of an oxazaborolidine via a hydrosilylation reaction to a methyl hydrosiloxane-dimethylsiloxane copolymer (Figure 4.40). The catalyst was used in the enantioselective borane reduction of ketones. 

Enantioselective borane reduction of ketones catalyzed by chiral oxazaborolidines. 

A polymer-bound oxazaborolidine catalyst enantioselective borane reductions of ketones, Tetrahedron Asymm. 1995, 6, 2755-2766. 

Use of thiaprohnol amino alcohols as hgands for enantioselective borane reduction of ketones and of a fiuorotitanium-TADDOLate to catalyse reduction of benzaldehyde has been described above imder OrganometaUics and Allylation Reactions, respectively. 

Corey, E. J., Bakshi, R. K., Shibata, S. Highly enantioselective borane reduction of ketones catalyzed by chiral oxazaborolidines. 

Chiral organophosphorus compounds have been found to act as catalysts in numerous enan-tioselective reactions. This review highlights recent developments in this area and more precisely in the kinetic resolution of secondary alcohols, the enantioselective borane reduction of ketones, and in the asymmetric C-C bond formation with the introduction of asymmetric two-center catalysts. 

Use of Chiral Phosphine-Borane Complexes in the Enantioselective Borane Reduction of Ketones. 84... 

As described in the catalytic enantioselective borane reduction of ketones using oxazaphospholidine-borane complexes, a mechanistic rationale has been proposed. Nevertheless, this mechanism cannot fully explain the enantioselec-tivity encountered. 

The CBS (Corey-Bakshi-Shibata) reagent is a chiral catalyst derived from proline. Also known as Corey s oxazaborohdine, it is used in enantioselective borane reduction of ketones, asymmetric Diels-Alder reactions and [3 + 2] cycloadditions. 

Fracl995 Franot, C., Stone, G.B., Engeli, R, Spondlin, C. and Waldvogel, E., A Polymer-Bound Oxazaborolidine Catalyst Enantioselective Borane Reductions of Ketones, Tetrahedron Asymmetry, 6 (1995) 2755-2766. 

---