Sodium borohydride nitro ketones

Potassium and sodium borohydride show greater selectivity in action than lithium aluminium hydride thus ketones or aldehydes may be reduced to alcohols whilst the cyano, nitro, amido and carbalkoxy groups remain unaffected. Furthermore, the reagent may be used in aqueous or aqueous-alcoholic solution. One simple application of its use will be described, viz., the reduction of m-nitrobenzaldehyde to m-nitrobenzyl alcohol ... 

Facial selectivities of spiro[cyclopentane-l,9 -fluorene]-2-ones 30a-30e were studied by Ohwada [96, 97]. The carbonyl tz orbital can interact with the aromatic % orbital of the fluorene in a similar manner to spiro conjugation [98-102]. The ketones 30 were reduced to alcohols by the action of sodium borohydride in methanol at -43 °C. The anti-alcohol, i.e., the syn addition product of the reducing reagent with respect to the substituent, is favored in all cases, irrespective of the substituent at C-2 or C-4 of the fluorene ring (2-nitro 30b syn anti = 68 32), 4-nitro... 

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. 

The reduction of ketones containing nitro groups to nitro alcohols is best carried out by borohydrides. 5-Nitro-2-pentanone was converted to 5-nitro-2-pentanol in 86.6% yield by reduction with sodium borohydride at 20-25°. Other nitro ketones gave 48.5-98.7% yields, usually higher than were obtained by Meerwein-Ponruiorf reduction [907]. 2-Acetamido-3-(p-nitrophenyl)-l-hydroxypropan-3-one was reduced with calcium borohydride at — 30° to 70% of threo- and 10% of er7tAro-2-acetamido-3-(p-nitrophenyl)propane-l,3-diol while sodium borohydride afforded a mixture of the above isomers in 25% and 47% yields, respectively [902]. 

Sodium borohydride is a mild and selective reducing reagent. In ethanol solution it reduces aldehydes and ketones rapidly at 25°C, esters very slowly, and is inert toward functional groups that are readily reduced by lithium aluminum hydride carboxylic acids, epoxides, lactones, nitro groups, nitriles, azides, amides, and acid chlorides. 

Reduction. An early report2 stated that aldehydes and a-hydroxy ketones are reduced by this reagent but that ketones, nitro compounds, carboxylic acids, and esters are not reduced. Borch and Durst,3 however, found that some ketones are reduced, but more slowly than with sodium borohydride. One advantage over the latter reagent is that lithium cyanohydridoborate is stable in acid up to pH 3 and hence can be used for reduction of groups sensitive to high pH (e.g., thiamine). 

Ethanolic solutions of sodium borohydride reduce aldehydes and ketones in the presence of epoxides, esters, lactones, acids, nitriles, and nitro groups. 1 419 xhe reaction is very selective for reactive functional groups such as acid chlorides, aldehydes or ketones, and the yields are commonly > 80%. The reduction of simple aldehydes or ketones that are part of more complex structures is perhaps the most prevalent use of sodium borohydride. The reduction of the ketone moiety in 91 to give the secondary alcohol in 92 (88% yield)l 0is a typical application involving sensitive functionality. Sodium borohydride often gives the 1,2-... 

Michael addition of the (S nitroester 95 to the unsaturated ketone 96 gave a mixture of 97 and the (22S)-isomer (207, 208). Sodium borohydride reduction of 97 in an acidic medium afforded the nitrodiol 98 in excellent yield. Reduction of the nitro group and subsequent lactam formation (99) proceeded smoothly when the nitrodiol 96 was refluxed with zinc and acetic acid. Further reduction of the amide 99 with LAH yielded the piperidine 100, which was converted into its iV-chloro derivative. Treatment of this compound with sodium methoxide effected dehydrochlorination which was... 

Examples of hydride reduction of aldehydes and ketones are shown in Figure 14.51. Notice in the first reaction that sodium borohydride selectively reduces the aldehyde in the presence of an ester nitro and nitrile groups are also tolerated. In the second reaction, the borohydride reduction of a ketone, the diastereoselectivity, reflects the steric hindrance to the approach of the methyl groups on the bridging carbon atom block the approach from the top face of the molecule. By contrast, little diastereoselectivity is observed in the reduction of 2-hydroxyclobutanone. The final example illustrates the reduction of an a,p-unsaturated ketone. 

Sodium and potassium borohydrides are above all used for reducing aldehydes and ketones (Sections 3.2.1, 3.2.2) a,p-ethylenic ketones are converted to mixtures [W3]. In alcoholic media or THF, they leave epoxides, esters and lactones, acids, amides, and most nitro compounds unreacted, but they reduce halides (Section 2.1), anhydrides (Section 3.2.6), quartemary pyridinium salts (Section 3.3), double bonds conjugated to two electron-withdrawing groups (Sections 3.2.9, 4.4), and CUPd... 

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