Reduction borohydride-alumina

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... 

A Ni-As(B) catalyst prepared by the borohydride reduction of alumina-supported nickel arsenate gave, on hydrogenation of 1-bromo-l 1-hexadecyne (13) in the presence of a small amount of acetone, a 97% yield of the alkene (14) having a 92 5 cis/trans ratio. No hydrogenolysis of the carbon-bromine bond occurred. "> 2 Borohydride reduction of cobalt acetate gave a Co(B) catalyst that was somewhat less active than Ni(B) but that was quite selective in alkyne semihydrogenations (Eqn. 16.20). ... 

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

Seyden-Penne, J. Reductions by Alumina- and Borohydrides in Organic Systlzesis VCH-Lavoisier Ihris, 1997. 

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

One of the most attractive features of borohydride reductions is that under micro-wave-enhanced conditions they can be performed in the solid state, and rapidly. We were attracted by the work of Loupy [57], and in particular Varma [58, 59] who has shown that irradiation of a number of aldehydes and ketones in a microwave oven in the presence of alumina doped NaBH4 for short periods of time led to rapid reduction (0.5-2 min) in good yields (62-93%). In our study [60] seven aldehydes and four ketones were reduced (Tab. 13.3). Again reduction was complete within 1 min, the products were of high purity (>95%), of high isotopic incorporation (95%, same as the NaBD4) and the reactions completely selective. 

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

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. 

Seyden-Penne, J. (1997) Reductions by the Alumina and Borohydrides in Organic Synthesis, 2nd edn, Wiley-VCH Verlag GmbH, New York. 

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. 

The Cannizzaro reaction, that is, the base-catalysed disproportionation of a carbonyl compound to an alcohol and a carboxylic acid, has gained some importance as an economically viable alternative to the reduction with borohydrides. However, the reaction is restricted to carbonyl compounds without any a-hydrogen, which do not undergo competing aldol reactions. Thus, mainly aromatic aldehydes are used for this kind of transformation. The protocols developed for microwave applications typically involve solvent-free conditions using alumina as the solid support. Under these conditions, a significant acceleration of the reaction was achieved. 

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. 

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). 

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