Borohydride preparation

NaBH4. See borohydrides. Prepared NaOMe plus B2H6. Used in organic reduc-... 

NB-Enantride (2). This name is the trademark of Aldrich for the borohydride prepared by treatment of the 9-BBN adduct of the benzyl ether of 6,6-dimethylbicyclo [3.1.1] hept-2-ene-2-ethanol (nopol, supplier Aldrich) with i-BuLi. 

The nitropyridines can be reduced to the corresponding aminopyridine and several new methods have been developed to achieve this transformation. 3-Nitropyridine is reduced in excellent yield by the mixed borohydride prepared from 1 equiv of ZrCU and 4 equiv of NaBFLi in THF under reflux <2000SL683>. 3-Nitropyridines may be reduced to the aminopyridine using sodium hydrosulfite in THF/H20 at room temperature <2005JME5104>. 2-Nitropyridine can be reduced to the amine in near quantitative yield by transfer hydrogenation in the presence of 10% Pd/C and recyclable polymer-supported formate, prepared from aminomethylpolystyrene resin and ammonium formate <2005SC223> (Equation 64). The resin is easily recovered by filtration and may be used up to 10 times. 

Per-acylated pyranoid and furanoid glycosyl bromides were easily reduced in high yield to the corresponding anhydroalditols by catalytic quantities of titanocene borohydride (prepared in situ from Cp2TiCl2 and NaBH4). ... 

In this preparation, phenyi-2-nitropropene is reduced to phenyl-2-nitropropane with sodium borohydride in methanol, followed by hydrolysis of the nitro group with hydrogen peroxide and potassium carbonate, a variety of the Nef reaction. The preparation is a one-pot synthesis, without isolation of the intermediate. 

The structure of the bicychc monoterpene borneol is shown in Figure 26 7 Isoborneol a stereoisomer of borneol can be prepared in the labora tory by a two step sequence In the first step borneol is oxidized to camphor by treatment with chromic acid In the second step camphor is reduced with sodium borohydride to a mixture of 85% isoborneol and 15% borneol On the basis of these transformations deduce structural formulas for isoborneol and camphor... 

Lynestrenol is the des-3-oxo derivative of norethindrone (28). It has been prepared through a similar synthetic pathway as aHylestrenol (37) (52), ie, addition of potassium acetyUde, rather than aHyl magnesium bromide, affords lynestrenol (73). Lynestrenol is also available from norethindrone (28). Reduction of the 3-keto group is accompHshed by treating norethindrone (28) with sodium borohydride in the presence of trifluoro- or trichloroacetic acid... 

Preparation. Sodium borohydride is manufactured from sodium hydride and trimethyl borate ia a mineral oil medium at about 275°C (26),... 

Other Borohydrides. Potassium borohydride was formerly used in color reversal development of photographic film and was preferred over sodium borohydride because of its much lower hygroscopicity. Because other borohydrides are made from sodium borohydride, they are correspondingly more expensive. Generally their reducing properties are not sufficiently different to warrant the added cost. Zinc borohydride [17611-70-0] Zn(BH 2> however, has found many appHcations in stereoselective reductions. It is less basic than NaBH, but is not commercially available owing to poor thermal stabihty. It is usually prepared on site in an ether solvent. Zinc borohydride was initially appHed to stereoselective ketone reductions, especially in prostaglandin syntheses (36), and later to aldehydes, acid haHdes, and esters (37). 

Higher nitroalkanes are prepared from lower primary nitroalkanes by a one-pot synthesis (69). Successive condensations with aldehydes and acylating agents are followed by reduction with sodium borohydride. Overall conversions in the 75—80% range are reported. 

The chain-growth catalyst is prepared by dissolving two moles of nickel chloride per mole of bidentate ligand (BDL) (diphenylphosphinobenzoic acid in 1,4-butanediol). The mixture is pressurized with ethylene to 8.8 MPa (87 atm) at 40°C. Boron hydride, probably in the form of sodium borohydride, is added at a molar ratio of two borohydrides per one atom of nickel. The nickel concentration is 0.001—0.005%. The 1,4-butanediol is used to solvent-extract the nickel catalyst after the reaction. 

AletalHydrides. Metal hydrides can sometimes be used to prepare amines by reduction of various functional groups, but they are seldom the preferred method. Most metal hydrides do not reduce nitro compounds at all (64), although aUphatic nitro compounds can be reduced to amines with lithium aluminum hydride. When aromatic amines are reduced with this reagent, a2o compounds are produced. Nitriles, on the other hand, can be reduced to amines with lithium aluminum hydride or sodium borohydride under certain conditions. Other functional groups which can be reduced to amines using metal hydrides include amides, oximes, isocyanates, isothiocyanates, and a2ides (64). 

Phenylstibine [58266-50-5] C H Sb, has been obtained by the reduction of phenyldiio do stihine [68972-61-2] CgH3l2Sb, (73) or phenyldichlorostibine [5035-52-9] 031130.2, (74) with lithium borohydride. It has also been prepared by the hydrolysis or methanolysis of phenylbis(trimethylsilyl)stibine [82363-95-9] C22H23Si2Sb (75). Diphenylstibine [5865-81-6] C22H22Sb, can be prepared by the interaction of diphenylchlorostibine [2629-47-2] C22H2QClSb, with either Hthium borohydride (76) or lithium aluminum hydride (77). It is also formed by hydrolysis or methanolysis of diphenyl (trimethylsilyl)stibine [69561-88-2] C H SbSi (75). Dimesitylstibine [121810-02-4] h.3.s been obtained by the protonation of lithium dimesityl stibide with trimethyl ammonium chloride (78). The x-ray crystal stmcture of this secondary stibine has also been reported. 

Since ivermectin (= 22,23-dihydroavermectin B ) is obtained by catalytic reduction of avermectin B, the same procedure using tritium gas convenientiy affords tritiated ivermectin (22,23- [JT]-22,23-dihydroavermectin B ). The preparation of a tritiated derivative containing a 22,23-double bond starts with the readily available 5-ketone, which is reduced with [JT]-sodium borohydride stereospecificaHy to a 5- [JT]-derivative (40). Carbon-14 labeled avermectins can be obtained by a biosynthetic process using sodium (l- C)propionate as labeled precursor (48). 

Good yields of phenylarsine [822-65-17, C H As, have been obtained by the reaction of phenylarsenic tetrachloride [29181-03-17, C H AsCl, or phenyldichloroarsine [696-28-6], C3H3ASCI25 with lithium aluminum hydride or lithium borohydride (41). Electrolytic reduction has also been used to convert arsonic acids to primary arsines (42). Another method for preparing primary arsines involves the reaction of arsine with calcium and subsequent addition of an alkyl haUde. Thus methylarsine [593-52-2], CH As, is obtained in 80% yield (43) ... 

The existence of bismuthine was first demonstrated by using a radioactive tracer, Bi (8). Acid treatment of a magnesium plate coated with Bi resulted in the hberation of a volatile radioactive compound. In subsequent experiments, magnesium bismuthide [12048-46-3], Mg Bi, was treated with acid the yield, however, was only one part of bismuthine for every 20,000 parts of bismuth dissolved. Attempts to prepare bismuthine by reduction of bismuth trichloride with a borohydride have not been particularly successful. Experimental quantities ate best prepared by disproportionation of either methylbismuthine [66172-95-0], CH Bi, or dimethylbismuthine [14381-45-4], C2H. Bi (7) ... 

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