Carbonyl compounds by sodium borohydride

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... 

Zadmard, R., Saidi, M.R., Bolourtchian, M. and Naldishab, L., Microwave-assisted reduction of beta-trimethylsilyl carbonyl compounds by sodium borohydride, Phosphorous, Sulphur Silicon Relat. Elem., 1998, 143, 63-66. 

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... 

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

A solvent-free reductive amination of carbonyl compounds using sodium borohydride supported on moist montmorillonite K10 clay also was facilitated by microwave irradiation (Scheme 8) [54]. Clay served the dual purpose of a Lewis acid and provided water from its interlayers to enhance the reducing ability of NaBH4. 

A solvent-free reductive amination protocol for carbonyl compounds using sodium borohydride supported on moist montmorillonite KIO clay is facihtated by MW irradiation (Scheme 2.2-44) [129]. Traditionally, sodium cyanoborohydride [130], sodium triacetoxyborohydride [131], and NaBH4 coupled with sulfuric acid [132] are reagents used for the reductive amination of carbonyl compounds the use of corrosive acids or cyanide-based reagents results in toxic-waste generation. The... 

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... 

Secondary amines can be prepared from the primary amine and carbonyl compounds by way of the reduction of the derived Schiff bases, with or without the isolation of these intermediates. This procedure represents one aspect of the general method of reductive alkylation discussed in Section 5.16.3, p. 776. With aromatic primary amines and aromatic aldehydes the Schiff bases are usually readily isolable in the crystalline state and can then be subsequently subjected to a suitable reduction procedure, often by hydrogenation over a Raney nickel catalyst at moderate temperatures and pressures. A convenient procedure, which is illustrated in Expt 6.58, uses sodium borohydride in methanol, a reagent which owing to its selective reducing properties (Section 5.4.1, p. 519) does not affect other reducible functional groups (particularly the nitro group) which may be present in the Schiff base contrast the use of sodium borohydride in the presence of palladium-on-carbon, p. 894. 

Arenetellurolates, ethenetellurolates, and alkanetellurolates prepared by reduction of diorgano ditellurium compounds with sodium borohydride in ethanol, THF/ethanol, or DMSO add to acetylenes in regioselective and iran.y-stereoselcctive reactions to produce aryl ethenyl tellurium products either predominantly or exclusively as (Z)-isomers. The yields are almost always higher than 70%. In reactions with acetylenic aldehydes, ketones, carboxylic acids, and esters the arenetellurolate becomes bonded to the carbon atom in a [i-position to the carbonyl group. 

A Michael addition of thiophenol to an a, j6-unsaturated carbonyl compound, followed by sodium borohydride reduction or addition of a metal-organic reagent, gives a y-phenylthioalcohol electrochemical reduction in dry DMF of the methanesulfonate of this alcohol yields a cyclopropane and a small amount of alkene [81] ... 

We focus first on the inherent reactivity of the carbonyl compound itself. An irreversible processes in which the addition product is stable is the most direct means of comparing the reactivity of carbonyl compounds. In these circumstances, the relative rate of reaction of different carbonyl compounds can be directly compared. One such reaction is hydride reduction. In particular, reductions by sodium borohydride in protic... 

Michael addition to (+)-pu]egone [( + )-12] is not only possible with carbon nucleophiles, but also nitrogen and sulfur compounds. Thus, reaction of (+)-pulegone with benzylamine, followed by reduction of the carbonyl group with sodium borohydride, gives (1 / .3/ ,4,S )-8-(ben-zylamino)menthol (24)28, used for the formation of chiral 1.3-oxazines which react with Grignard reagents diastereoselectively (Section D. 1.3.1.4.). 

These are stable compounds which do not polymerise or autoxidise. For the most part, pyrrole aldehydes and ketones are typical aryl ketones, though less reactive, especially when at the a-position, due to the reduced electrophilicity of the carbonyl carbon resulting from mesomeric interaction with the ring nitrogen. They can be reduced to alkylpyrroles by the Wolff-Kishner method, or by sodium borohydride via elimination from the initial alcoholic product. ... 

The key step in the reduction of a carbonyl compound by either lithium aluminum hydride or sodium borohydride is the transfer of a hydride ion from the metal to the carbonyl carbon. In this transfer the hydride ion acts as a nucleophile. The mechanism for the reduction of a ketone by sodium borohydride is illustrated here. 

---