Chlorodiisopinocampheylborane

In cases where Noyori s reagent (see p. 102f.) and other enantioselective reducing agents are not successful, (+)- or (—)-chlorodiisopinocampheylborane (Ipc BCl) may help. This reagent reduces prochiral aryl and tert-alkyl ketones with exceptionally high enantiomeric excesses (J. Chandrasekharan, 1985 H.C. Brown, 1986). The initially formed boron moiety is usually removed hy precipitation with diethanolamine. Ipc2BCl has, for example, been applied to synthesize polymer-supported chiral epoxides with 90% e.e. from Merrifield resins (T. Antonsson, 1989). 

Oxidation reactions r-Butyl hydroperoxide-Dialkyl tar-trate-Titanium(IV) isopropoxide, 51 m-Chloroperbenzoic acid, 76 Reduction reactions Chlorodiisopinocampheylborane, 72 Diisobutylaluminum hydride-Tin(II) chloride- (S) -1 - [ l-Methyl-2-pyrrolidi-nyljmethylpiperidine, 116 Lithium borohydride, 92 Lithium tri-sec-butylborohydride, 21 B-3-Pinanyl-9-borabicyclo[3.3.1]-nonane, 249... 

Using boron-based reagents Chlorodiisopinocampheylborane, 72 Lithium triethylborohydride, 205 Sodium cyanoborohydride-Tin(II) chloride, 280... 

B-Chlorocatecholborane, 47 Chlorodiisopinocampheylborane, 72 Chlorodimethoxyborane, 73 B-Crotyl-9-borabicyclo[3.3.1]nonane, 215... 

The use of oxazaborolidines as asymmetric reduction catalysts257 and the enantioselectivity of diphcnyloxazaborolidinc reduction of ketones have been reviewed.258 Large-scale practical enantioselective reduction of prochiral ketones has been reviewed with particular emphasis on the Itsuno-Corey oxazaborolidinc and Brown s 5-chlorodiisopinocampheylborane (Ipc2BCl) as reagents.259 Brown himself has also reviewed the use of Ipc2BCl.260 Indolinoalkylboranes in the form of dimers have been confirmed by 11B NMR as the products of the reduction of trifluoroacetylindoles by diborane.261... 

Asymmetric reduction of the ketone on a 1.0-g (4.0-mmol) scale to provide (R)-(-)-2,2-diphenylcyclopentanol (96% ee) has been reported employing (+)-( -chlorodiisopinocampheylborane however, the reaction is extremely slow and inefficient [70% yield, 5 days, 2.6 equiv of (+)-p-chlorodiisopinocampheylborane].5 Other efforts to obtain enantiomerically pure 1 by means of enzymatic hydrolysis of the corresponding racemic acetates using horse liver acetone powder (HLAP) and pig... 

The oxazaborolidine-catalyzed borane reduction to prepare (R)-1 is an improvement over existing methods such as the p-chlorodiisopinocampheylborane reduction,6 and enzymatic resolution14 for several reasons. First, the reaction uses an easily obtained catalytic reducing agent that provides the chiral alcohol in 92% ee. Secondly, the reaction proceeds at a reasonable rate (6-8 hr) and affords the chiral alcohol (92% ee) In nearly quantitative yield (97%). Finally, the work-up, isolation and purification of the product is straightforward and requires no column chromatography, only bulb-to-bulb distillation and recrystallization, affording (R)-1 in 75% yield with 97% ee. In addition, the catalyst precursor, (S)-a,a-diphenylpyrrolidinemethanol. can be easily recovered in excellent yield. 

Related Reagents. (+)-S-Chlorodiisopinocampheylborane Diisopinocampheylboron Trifluoromethanesulfonate Dilongi-folylborane (/ ,/J)-2,5-Dimethylborolane B-Methoxydiiso-pinocampheylborane Monoisopinocampheylborane. 

The simple steric model for the transition state may be used to predict the absolute configuration of the product. The related reagent (+)-B-Chlorodiisopinocampheylborane reduces ketones with greater ease and efficiency (eq 12). ... 

During the total synthesis of rhizoxin D by J.D. White et al., an asymmetric aldol reaction was utilized to achieve the coupling of two key fragments. " The aldol reaction of the aldehyde and the chiral enolate derived from (+)-chlorodiisopinocampheylborane afforded the product with a diastereomeric ratio of 17-20 1 at the CIS stereocenter. During their studies. White and co-workers also showed that the stereochemical induction of the chirai boron substituent and the stereocenters present in the enolate reinforce each other thus representing a matched aldol reaction. 

Another excellent way to produce enantiomerically pure secondary alcohols is to use chiral organoboranes. After the work pioneered by Brown, many reagents have been developed, such as p-3-pinanyl-9-borabicyclo-[3.3.1]-nonane (Alpine-Borane) (2) and chlorodiisopinocampheylborane (Ipc2BCl) (3) [4]. The latter is now commercially available at scale, and is a useful reagent to reach high chemical and optical yields. A good example of its efficacy has been reported in the preparation of the antipsychotic, BMS 181100, from Bristol-Myers. 

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