Reduction chlorodiisopinocampheylborane

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... 

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. 

In the context of finding out efficient syntheses of enantiomerically pure multifunctional molecules containing a chiral quaternary carbon atom. Brown reported the KR of representative a-alkyl-P-ketoesters and a-tertiary ketones with B-chlorodiisopinocampheylborane (DlPCl), with the simultaneous preparation of the alcohols with de and ee >90% [67]. As an example, reduction of the Dieckmann ester 89 with O.SOMequiv of (—)-DlPCl at room temperature for 2h afforded, after the usual diethanolamine work-up, the recovered ketone (R)-89 in 43% yield (90% ee). A 37% yield of the methyl l-methyl-2-hydroxycyclopentanecarboxylates 90 with a cis trans ratio 3 97 was reported. The (IS, 2S)-trans-isomer showed 96% ee. Increasing the ratio reagent substrate improved the efficiency of the KR of the ketone, at the expense of the diastereomeric excess and enantiomeric excess of the... 

Ramachandran, P. V., Pitre, S., Brown, H. C. 2002. Selective reductions. 59. Effective intramolecular asymmetric reductions of a-, P-, and y-keto acids with diisopinocampheylborane and intermolecular asymmetric reductions of the corresponding esters with B-chlorodiisopinocampheylborane. J. Org. Chem. 67 5315-5319. 

SCHEME 2.137 Brown s (-)-chlorodiisopinocampheylborane [(-)-IpCjBCl] and significant examples of reduction. 

Protection of Phenols. Methoxyethoxymethyl chloride can also be used to protect phenols. The conditions for its introduction are similar to those used for alcohols (NaH, THE, 0°C MeOCH2CH20CH2Cl, 0°C 25°C, 2 h, 75% yield). In contrast to the alcohol derivatives, phenolic MEM ethers can be cleaved with Trifluoroacetic Acid (CH2CI2, 23 °C, 1 h, 74% yield). 1 M HCl (THE, 5 h, 60 °C) and HBr/EtOH will also effect cleavage. In general, the cleavage conditions used for alcohols are also effective with the phenolic derivatives. During an examination of the asymmetric reduction of an acetophenone derivative with (+)-B-Chlorodiisopinocampheylborane, it was found that a phenolic MEM ether was slowly cleaved (eq 4). ... 

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