Reduction chiral boron reagents

Asymmetric Reduction of Unsymmetrical Ketones Using Chiral Boron Reagents Review Synthesis 1992, 605. 

Reviews on stoichiometric asymmetric syntheses M. M. Midland, Reductions with Chiral Boron Reagents, in J. D. Morrison, ed., Asymmetric Synthesis, Vol. 2, Chap. 2, Academic Press, New York, 1983 E. R. Grandbois, S. I. Howard, and J. D. Morrison, Reductions with Chiral Modifications of Lithium Aluminum Hydride, in J. D. Morrison, ed.. Asymmetric Synthesis, Vol. 2, Chap. 3, Academic Press, New York, 1983 Y. Inouye, J. Oda, and N. Baba, Reductions with Chiral Dihydropyridine Reagents, in J. D. Morrison, ed., Asymmetric Synthesis, Vol. 2, Chap. 4, Academic Press, New York, 1983 T. Oishi and T. Nakata, Acc. Chem. Res., 17, 338 (1984) G. Solladie, Addition of Chiral Nucleophiles to Aldehydes and Ketones, in J. D. Morrison, ed., Asymmetric Synthesis, Vol. 2, Chap. 6, Academic Press, New York, 1983 D. A. Evans, Stereoselective Alkylation Reactions of Chiral Metal Enolates, in J. D. Morrison, ed., Asymmetric Synthesis, Vol. 3, Chap. 1, Academic Press, New York, 1984. C. H. Heathcock, The Aldol Addition Reaction, in J. D. Morrison, ed., Asymmetric Synthesis, Vol. 3, Chap. 2, Academic Press, New York, 1984 K. A. Lutomski and A. I. Meyers, Asymmetric Synthesis via Chiral Oxazolines, in J. D. Morrison, ed., Asymmetric Synthesis, Vol. 3, Chap. 

Midland MM (1983) Reductions with chiral boron reagents. In Morrison JD (ed) Asymmetric synthesis. Academic, New York, vol 2, chap 2, p 45 Itsuno S (1996) The Alembic, Morton Performance Chemicals 53 1 Fiaud JC, Kagan HB (1969) Bull Soc Chim Fr 2742 Borch RF, Levitan SR (1972) J Org Chem 37 2347 Grundon MF, McCleery DG, WUson JW (1976) Tetrahedron Lett 295 Grundon MF, McCleery DG, WUson JW (1981) J Chem Soc Perkin Trans 1 231 Johnson CR, Stark CJ (1979) Tetrahedron Lett 4713... 

In an attempt to prepare alkylamines by asymmetric reduction of imines with chiral hydride reagents, diphenylphosphinyl imines (38), prepared by reaction of ketoximes (39) with chlorodiphenylphosphine [(Cg 115)2 PCI], were reduced in the presence of a variety of chiral aluminum and boron hydride reagents43. Among the most promising reagents was BINAHL-H44 (40), a chiral hydride compound prepared by the modification of lithium... 

The CBS-reduction [137] of prochiral ketones is a well-known process which employs a chiral oxazaboroHdine as catalyst and BHs-THF or catecholborane as stoichiometric reductants. It is believed that the active catalytic species is a LLA, resulting from coordination of the oxazaborolidine nitrogen with the boron reagent to render the oxazaborolidine boron atom highly Lewis acidic [87]. Similarly, Corey... 

Since the first asymmetric reduction of ketones with chiral borohydrides by Itsuno et al. [ 1 ], a number of studies on the asymmetric reduction of ketones with chiral borane reagents have been demonstrated [2]. Corey s oxazaborolidines are some of the most successful reagents [3 ]. The effect of fluorine substituents was examined in the asymmetric reduction of acetophenone with LiBH4 by the use of chiral boronates (73) obtained from substituted phenyl boronic acid and tartaric acid [4]. Likewise, 3-nitro, fluorine, and trifluoromethyl groups on the 3- or 4-position provided enhanced stereoselection (Scheme 5.20). 

Boronic esters have been used in a wide range of transformations. These useful reagents have been transformed into numerous functional groups and are essential reagents for several C-C bond-forming reactions. Transition metal-catalyzed hydroboration of olefins often leads to mixtures of branched and linear products. Several groups have reported asymmetric reductions of vinyl boronic esters [50-52] with chiral rhodium P,P complexes however, the first iridium-catalyzed reduction was reported by Paptchikhine et al (Scheme 10) [53]. 

One popular method that has been apphed to industrial processes for the enantio-selective reduction of prochiral ketones, leading to the corresponding optically active secondary alcohols, is based on the use of chiral 1,3,2-oxazaborolidines. The original catalyst and reagent system [diphenyl prolinol/methane boronic acid (R)] is known as the Corey-Bakshi-Shibata reagent. Numerous examples... 

In addition to being useful reagents for the reductions of carbonyl compounds, boron-based reagents can also be used for the conversion of an alkene to a wide variety of functionalized alkanes. Because the majority of these reagents carry a terpene substituent, they are discussed under these chiral pool materials (Chapter 5). 

The modification of aluminum or boron hydrides with chiral protic substances, such as R OH or RR NH, generates useful reagents for the asymmetric reduction of prochiral ketones or imines leading to optically active secondary alcohols and amines, respectively. Some reviews have appearered in the literature. ... 

Chiral modification is not limited to boronate and aluminate complexes. Boranes or alanes are partially decomposed with protic substances such as chiral amines, alcohols or amino alcohols to form useful reagents for enantioselective reduction of carbonyl compounds. For example, reduction of acetophenone with borane modified with the amines (65) to (67) gives (5)-l-phenylethyl alcohol with 3.5-20%... 

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