Sodium borohydride reduction of carbonyl compounds

Alumina-sodium borohydride, reduction of carbonyl compounds with, 16 572-573 Alumina sols, gelation of, 23 77 Alumina-supported iodobenzene diacetate (IBD), 16 570... 

Sodium borohydride and lithium aluminum hydride react with carbonyl compounds in much the same way that Grignard reagents do except that they function as hydride donors rather than as carbanion sources Figure 15 2 outlines the general mechanism for the sodium borohydride reduction of an aldehyde or ketone (R2C=0) Two points are especially important about this process... 

The final stages of the successful drive towards amphotericin B (1) are presented in Scheme 19. Thus, compound 9 is obtained stereoselectively by sodium borohydride reduction of heptaenone 6a as previously described. The formation of the desired glycosida-tion product 81 could be achieved in dilute hexane solution in the presence of a catalytic amount PPTS. The by-product ortho ester 85 was also obtained in approximately an equimolar amount. Deacetylation of 81 at C-2, followed sequentially by oxidation and reduction leads, stereoselectively, to the desired hydroxy compound 83 via ketone 82. The configuration of each of the two hydroxylbearing stereocenters generated by reduction of carbonyls as shown in Scheme 19 (6—>9 and 82->83) were confirmed by conversion of 83 to amphotericin B derivative 5 and comparison with an... 

Reduction of carbonyl compounds can be carried out in an aqueous medium by various reducing reagents. Among these reagents, sodium borohydride is the most frequently used. The reduction of carbonyl compounds by sodium borohydride can also use phase-transfer catalysts (Eq. 8.4),10 inverse phase-transfer catalysts,11 or polyvinylpyridines12... 

Reduction of Carbonyl Compounds to Alcohols - Sodium Borohydride-... 

Scheme 6.38 Reduction of carbonyl compounds using alumina-supported sodium borohydride.

Sodium borohydride is a much milder reducing agent than lithium aluminium hydride and like the latter is used for the reduction of carbonyl compounds like aldehydes and ketones. However, under normal conditions it does not readily reduce epoxides, esters, lactones, acids, nitriles or nitro groups. 

Sodium dithionite is well established [ 1 ] as a powerful reducing agent under alkaline conditions. Its redox potential is close to that of sodium borohydride [2] and, in several respects, there are advantages in the use of sodium dithionite as an alternative to the metal hydrides under phase-transfer catalytic conditions, particularly in the reduction of carbonyl compounds [3],... 

Varma, R.S. and Saini, R.K., Microwave-assisted reduction of carbonyl compounds in solid state using sodium borohydride supported on alumina, Tetrahedron Lett., 1997, 38, 4337-4338. 

Ventron also offers Sodium borohydride-SWS, a stabilized water solution of average composition 40% sodium hydroxide and 12% sodium borohydride, sp. gr. 1.4. It is stable indefinitely and can be used as such for reduction of carbonyl compounds or it can be diluted with water, methanol, or ethanol. Most aldehydes are reduced so rapidly that condensations promoted by the alkali do not interfere. For reduction of an a,/3-unsaturated aldehyde, however, the strongly basic reagent is unsatisfactory and should be diluted to the desired concentration and neutralized with carbon dioxide. The neutralized reagent should be used immediately, since the borohydride is no longer stable and decomposes at 25° at the rate of 4.5% per hr. 

Reaction media. While alcoholic solvents are used in conventional reduction of carbonyl compounds with sodium borohydride, they can be replaced with hexane if alumina or silica geF is added (heterogeneous conditions). In a refluxing mixture of DME and methanol, NaBH4 reduces methyl methoxybenzoates to the corresponding benzylic alcohols.- Stereoselectivity changes are observed in the reduction of 2-substituted cyclohexanones when conducted in DMSO. ... 

Lithium aluminium hydride is a more powerful reducing agent than sodium borohydride and reduces most of the commonly encountered organic functional groups (see Table 7.3). It reacts readily with water and other compounds that contain active hydrogen atoms and must be used under anhydrous conditions in a non-hydroxylic solvent diethyl ether and THF are commonly employed. Lithium aluminium hydride has found widespread use for the reduction of carbonyl compounds. Aldehydes, ketones, esters, carboxylic acids and lactones can all be reduced smoothly to the corresponding alcohols under mild conditions. Carboxylic amides are converted into amines or aldehydes, depending on the conditions and on the... 

With silica as a support and sodium borohydride as a reducing agent, cyclohexanol has been prepared from cyclohexanone in less than 3 min using a scientific microwave unit (Scheme 6.9). The reduction of carbonyl compounds by sodium borohydride is traditionally time consuming. It can take 2-4 h to reach completion, this equating to a whole laboratory period, and usually another lab period is required for product isolation and characterization. Using the microwave procedure, the entire experiment can be completed in one 2.5 h session. The reaction was performed in closed tubes... 

Table 19. Asymmetric reduction of carbonyl compounds with sodium borohydride in the presence of BSA.

Most reductions of carbonyl compounds, including aldehydes and ketones, are now accomplished by transfer of hydride ions from boron or aluminum hydrides. We have already seen the use of sodium borohydride to reduce the carbonyl group of aldehydes and ketones to hydroxyl groups (Section 16.11A) and the use of lithium aluminum hydride to reduce not only aldehyde and ketone carbonyl groups but also carboxyl groups to hydroxyl groups (Section 17.6A). 

The reduction of carbonyl compounds in aqueous media has been carried out by a number of reagents under mild conditions. The most frequently used reagent is sodium borohydride, which can also be used using phase-transfer catalysts or inverse phase transfer catalyst in a two phase medium in the presence of surfactants. 

E. Santaniello, F. Ponti, and A. Manzocchi. Reduction of carbonyl compounds by sodium borohydride absorbed on alumina. Synthesis, 1978, 891. 

We saw in Section 17.4 that the most common method for preparing alcohols, both in the laboratory and in living organisms, is by the reduction of carbonyl compounds. Aldehydes are reduced with sodium borohydride (NaBH4) to give primary alcohols, and ketones are reduced similarly to give secondary alcohols. 

Most reductions of carbonyl compounds are done with reagents that transfer a hydride from boron or aluminum. The numerous reagents of this type that are available provide a considerable degree of selectivity and stereochemical control. Sodium borohydride and lithium aluminum hydride are the most widely used of these reagents. Sodium borohydride is a mild reducing agent which reacts rapidly with aldehydes and ketones but quite slowly with esters. Lithium aluminum hydride... 

Although hydride anion is an excellent nucleophile, it is also an extremely strong base, which reacts with far too many other functional groups to be a useful reagent for the reduction of carbonyl compounds. However, the basicity of the hydride ion is greatly diminished in sodium borohydride (NaBH ) and hthium aluminum hydride (LiAIH ). Borohydride and aluminum hydride are excellent sources of hydride anions for the reduction of carbonyl compounds. 

Varma and Saini (1997) reported that alumina supported sodium borohydride can be used for the reduction of carbonyl compounds to corresponding alcohols under microwave irradiation, using solventless conditions giving 62-93% yield. 

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