Ketones with borane

Reaction of halo ketones or diazo ketones with boranes 10-112 Carbonylation of alkyl halides... 

Other S/N ligands have been investigated in the enantioselective catalytic reduction of ketones with borane. Thus, Mehler and Martens have reported the synthesis of sulfur-containing ligands based on the L-methionine skeleton and their subsequent application as new chiral catalysts for the borane reduction of ketones." The in situ formed chiral oxazaborolidine catalyst has been used in the reduction of aryl ketones, providing the corresponding alcohols in nearly quantitative yields and high enantioselectivities of up to 99% ee, as shown in Scheme 10.60. 

They were applied as effective reagents for the asymmetric reduction of ketones with borane. 

Table 11.2 summarises a number of examples of the enantioselective reduction of achiral ketones with borane in the presence of 0.1-0.2 equiv. of catalyst 3. 

Figure 1.27. Asymmetric reduction of ketones with borane catalyzed by oxazaborolidines.

Reaction of halo ketones or diazo ketones with boranes 0-102 Carbonylation of alkyl halides 0-104 Reaction between acyl halides and organometallic compounds 0-105 Reaction between other acid derivatives and organometallic compounds... 

Asymmetric reduction of prochiral aromatic ketones with borane cat-... 

The asymmetric reduction of ketones with borane or with NaBH4/Me3SiCl, catalysed by P-hydroxysulfoximines, afforded secondary alcohols in high yields with good enantioselectivities [241,242],... 

A more chemically robust polymer-supported chiral catalyst, based on a,a-diphenyl-L-prolinol, was designed by Kell et a/.11411 for reduction of prochiral ketones with borane. 

The use of chiral oxazaborolidines as catalysts for the enantioselective addition of alkynylboranes to aldehydes took place in a manner analogous to the asymmetric reduction of ketones with boranes mediated by proline-derived oxazaborolidines (Equation (127)).587 Addition of alkynylboranes to A-aziridinylimines provided a convenient method to prepare allenes from carbonyl compounds (Equation (128)).5... 

Enantioselective Ketone Reduction. After the pioneering work of Itsuno et al., Corey s group isolated the 1,3,2-oxazaborolidine derived from chiral a,a-diphenyl-2-pyrrolidinemethanol (2) and applied it (and also other related B-alkyl compounds) to the stereoselective reduction of ketones with borane-tetrahydrofuran, borane-dimethyl sulfide (BMS) or catecholborane.It was named the CBS method (after Corey, Bakshi, and Shibata). Since then, the CBS method has become a standard and has been extensively used, specially for aromatic and a,p-unsaturated ketones, not only in academic laboratories but also in industrial processes. ... 

A similar approach was employed in our laboratory for the development of molecularly imprinted catalysts for the enantio-selective reduction of prochiral ketones with borane (CBS reaction) [122]. A stable, polymerisable transition state analogue of this reaction leading to the formation of one particular enantiomer product was prepared (Fig. 4.9). After polymerisation, the template molecule can... 

Reduction using boranes. A practical modification of the oxazaborolidine-catalyzed reduction of ketones with borane is to replace the trialkylborane component with trimethyl borate. For the reduction of (3-silyl and ( -stannyl enones the use of 80 is advocated. ... 

Reduction. Secondary alcohols with moderate ee values are obtained from the reduction of ketones with borane in the presence of such a complex. 

Mediation of reduction. The reduction of P-hydroxy ketones with borane-pyridine... 

Reduction of ketones with borane. The basic principle for employing chiral... 

One of the outstanding discoveries of recent years is the enantioselective reduction of prochiral ketones with borane in the presence of catalytic amounts of oxazaborolidenes obtained from L-proline (reaction 9.10), and termed... 

There are also a variety of asymmetric catalytic reactions which may produce optically active alcohols. Metalo-organic compounds have been reported to play an essential role in some of them. One of these reactions is enantioselective reduction of pro-chiral ketones with borane in which BHj-SMe adduct are used as reductant. It also needs a chiral ligand along with aluminum isopropoxide to prepare enantioenrich compounds (reaction 7.7). Fu and Uang used (R)-binaphthol as chiral ligand and without use of AKOTrlj, reached 50% yield with no enantioselectivity in production of phenyl ethanol 63, from acetophenone 62, by BH -SMe even after 24 hours [54]. But in the presence of both, at 40°C, 96% yield with 74%... 

Hydroboration of Ketones with Boranes from ot-Pinenes and the Non-linear Effect in Asymmetric Reactions... 

Hydroboration of Ketones with Boranes from a-Pinenes... 

A new catalyst (46) (Figure 5) for asymmetric reduction of ketones with borane gives moderate to good enantioselectivities. It was designed to provide a Lewis basic site (the pyridyl nitrogen atom) in addition to the Lewis acidic site so that coordination of borane would enable intramolecular hydride delivery [structure (48)]. The success of this strategy was confirmed by the inferior enantioselectivity of the analogue (47), which has no Lewis basic site. ... 

Highly enantioselective reduction of heterocyclic aromatic ketones with borane and the spiroborate ester derived from (S)-diphenyl prolinol... 

Asymmetric reduction of prochiral ketones is one of most efficient method of the introduction of chirality in the synthesis of non-racemic biologically active compounds. Derived from chiral (S)-diphenyl prolinole the amino borate ester 1 has been prepared, fully characterized and used as highly effective catalyst for asymmetric reduction of ketons with borane. The optically pure alcohols 3 have been prepared using only 1 mol % of catalyst 1 in enantioselectivity up to 97%. 

---