Sodium borohydride-alumina

Sodium aluminum chloride, 435 Sodium amalgam, 310, 416-417 Sodium amide-Sodium r-butoxide, 417-418 Sodium azide-Triphenylphosphine, 418 Sodium bis(2-methoxyethoxy)aluminum hydride, 166,418-420 Sodium borohydiidc, 323,420-421 Sodium borohydride-Alumina, 421 Sodium borohydride-Bis(2,4-pentane-dionato)copper(ll), 421 Sodium borohydride-Cerium(Ill) chloride,... 

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

A solution of 1 g of the dione in 200 ml of methanol at 0° is treated with 75 mg of sodium borohydride and the mixture is kept for 2 hr. After addition of 0.1 ml of acetic acid the mixture is concentrated to ca. 20 ml. Dilution with water gives 0.9 g of crystals which are chromatographed on 20 g of unwashed alumina. Elution with benzene-ether (40 60) yields 0.73 g of the methyl-hydroxytestosterone, mp 245-249°, which after crystallization from acetone has mp 255-256° [a] 111° (CHCI3). 

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

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

Carbonyl compounds addition to, 73 659 a-alkylation of, 73 658s reduction with alumina—sodium borohydride, 76 572-573 reduction with aluminum alkoxides, 76 572... 

Catalytic reduction of cytidine in water over rhodium on alumina yields the tetrahydro derivative [l-(/3-D-ribofuranosyl)-4-aminotetrahydropyrimidin-2(l//)-one] and l-( 3-D-ribofuranosyl)tetrahydropyrimidin-2(l/0-one as the major products [680]. The former hydrolyses readily to give tetrahydrouridine,which is a potent inhibitor of human liver deaminase. The latter compound is also formed by sodium borohydride reduction of 5,6-dihydrouridine. 

A very active elemental rhodium is obtained by reduction of rhodium chloride with sodium borohydride [27]. Supported rhodium catalysts, usually 5% on carbon or alumina, are especially suited for hydrogenation of aromatic systems [iTj. A mixture of rhodium oxide and platinum oxide was also used for this purpose and proved better than platinum oxide alone [i5, 39]. Unsaturated halides containing vinylic halogens are reduced at the double bond without hydrogenolysis of the halogen [40]. 

Varma reported a facile and rapid method for the reduction of aldehydes and ketones to the respective alcohols, using alumina-supported sodium borohydride and microwave irradiation under solvent-free conditions. Aldehydes tend to react at room temperature, while for the reduction of ketones, short microwave irradiation of 30-180 s was applied to produce the corresponding alcohols in 62-92% yield. With unsaturated carbonyl compounds, reduction at the conjugated C=C bond might occur as a side reaction under these conditions (Scheme 4.9)26. 

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. 

Methyl O-methyl-7-ketopodocarpate (324) was reduced with sodium boro-hydride to the hydroxyester 325. Birch reduction of 325 followed by acidic hydrolysis and esterification with diazomethane afforded the dienone 326. Reduction of 326 with sodium borohydride followed by acetylation and treatment of the epimeric mixture with m-chloroperbenzoic acid afforded 327. The latter was rearranged with BF3 in ether to yield the ketone 328 which on chromatography over alumina gave the dienone 329. Reaction of 329 with maleic anhydride in refluxing toluene followed by esterification... 

The relatively inexpensive and safe sodium borohydride (NaBH4) has been extensively used as a reducing agent because of its compatibility with protic solvents. Varma and coworkers reported a method for the expeditious reduction of aldehydes and ketones that used alumina-supported NaBH4 and proceeded in the solid state accelerated by microwave irradiation (Scheme 7) [50]. The chemoselectivity was apparent from the reduction of frarcs-cinnamaldehyde to afford cinnamyl alcohol. 

Nitrophenyl Phenyl Tellurium5 Under nitrogen, 0.29 g (0.70 mmol) of diphenyl ditellurium are reduced with 0.03 g (0.73 mmol) of sodium borohydride in 5 ml of hexamethylphosphoric triamide at 70-80° with stirring for 0.5 h. Then 0.14 g (0,73 mmol) of copper(l) iodide are added whereupon the mixture turns black. 0.18 g (0.73 minol) of l-iodo-2-nitrobenzene are added and the mixture is stirred well and heated at 80 90° for 1.5 h. The mixture is cooled, water is added, the whole is extracted with diethyl ether, the extract is washed with concentrated sodium chloride solution, and the organic layer is dried with anhydrous sodium sulfate. The solvent is evaporated under vacuum and the residue is chromatographed on a short column of alumina with hexane as eluent. Fractions containing the product are combined and evaporated to dryness and the residue is rccrystallized from ethanol yield 0.22 g (95%) m.p. 94°. 

Nagata s method. Reduction of the ketone with sodium borohydride stereoselec-tively led to the alcohol, which on repeated chromatography on basic alumina cyclized to the iminoether, 165. Its conversion into 14-oxodendrobine (97) was achieved by tosylation to the tosylamide and subsequent basic hydrolysis. The authors developed an alternative route from cyanoketone 164 to 14-oxodendrobine (97) by hydrolyzing the nitrile under acidic conditions. The acid formed was esterified with diazomethane and the ketone 166 was reduced stereoselectively with sodium borohydride. Subsequent saponification and acidic lactonization led to 14-oxodendrobine (97). Inubushi et al. also used Borch s method to convert 14-oxodendrobine (97) into dendrobine (82) via the lactimether 167 and reduction. 

Reduction of acid chlorides. Sodium borohydride impregnated on alumina reduces acid chlorides to primary alcohols (equation I). 

Reaction of a-haloketones with 0,0-diethyl hydrogen phosphorodithiate and sodium borohydride, supported on alumina, under microwave irradiation for a few minutes, gave thiiranes in good or excellent yield (Scheme 100 Table 19) <2002S2344>. (See also Scheme 11 and Equation 15). 

The hydrogenation of 4-vinylcyclohexene (46) to 4-ethylcyclohexene (47) was also reported to take place over a supported nickel arsenide, Ni-As(B), which was prepared by the sodium borohydride reduction of nickel arsenate supported on either silica 2,83 or alumina. " These catalysts, however, fimction best in the presence of additives. When the reaction was run in pentane at 125 C and 25 atmospheres of hydrogen in the presence of a small amount of acetone, the product mixture at 96% conversion was 96% 4-ethylcyclohexene (47) and 4% ethylcyclohexane (48). No isomeric olefins were detected. " ... 

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