Sodium borohydride-Methanol

Biphenylyl ditelluride 33 was treated with sodium borohydride/methanol in the presence of trifluoromethyl iodide or bromide in tetrahydrofuran (THF) to give trifluoromethyl biphenylyl telluride 34 (Eq. 7). 

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. 

Methyl borate is beheved to be the boric acid ester produced in the largest quantity, approximately 8600 metric tons per year (28). Most methyl borate is produced by Morton International and used captively to manufacture sodium borohydride [16940-66-2]. Methyl borate production was studied in detail during the 1950s and 1960s when this compound was proposed as a key intermediate for production of high energy fuels. Methyl borate is sold as either the pure compound or as the methanol azeotrope that consists of approximately a 1 1 molar ratio of methanol to methyl borate. 

The least troublesome routes to 3,4-dihydro- and 1,2,3,4-tetrahydro-quinazoline are probably the reduction of quinazoline by sodium borohydride, in water for the former or in methanol for the latter. Both must be isolated as salts. The dihydroquinazoline may be formed also by reduction with LAH in ether (65JHC157). In contrast, 5,6,7,8-tetrahy-droquinazoline is best made by primary synthesis from 2-formylcyclohexanone and for-mamide (57CB942) or from cyclohexanone and trisformamidomethane (60CB1402). 

Potassium borohydride is similar in properties and reactions to sodium borohydride, and can similarly be used as a reducing agent for removing aldehydes, ketones and organic peroxides. It is non-hygroscopic and can be used in water, ethanol, methanol or water-alcohol mixtures, provided some alkali is added to minimise decomposition, but it is somewhat less soluble than sodium borohydride in most solvents. For example, the solubility of potassium borohydride in water at 25° is 19g per lOOmL of water (as compared to sodium borohydride, 55g). 

A solution of 2 g of sodium borohydride in 5 ml of water is added at room temperature to a solution of 1 g of 3a-hydroxy-5jS-pregnane-l 1,20-dione in 15 ml of methanol. Almost immediately, crystals begin to form. After the mixture has been kept overnight, the precipitate is collected with suction to yield 0.8 g of the diol, mp 230-232°. The analytical sample, crystallized once more from aqueous methanol, melts at 231.4-232.6° [a]p 31.2° (acetone). Reported mp 236-238°. 

Refluxing 3a-hydroxy-5)5-pregnane-ll,20-dione in methanol overnight with sodium borohydride gives the 3a,llj5,20jS-triol in 85% yield with mp 233-235°, [ ][) 38.9° (dioxane). 

When 3a,17a-dihydroxy-5jS-pregnane-ll,20-dione is allowed to react at room temperature overnight with sodium borohydride in aqueous methanol, no crystals form and only 5j5-pregnane-3a,l ljS,17a,20j5-tetrol is isolated in good yield. If the reaction is halted at the end of 3 h y the addition of water and extraction with chloroform, it is possible xo obtain a 55% yield of 3a,17a,20jS-trihydroxy-5j5-pregnan-ll-one, mp 218-220°,after recrystallization of the chloroform residue from aqueous methanol. The analytical sample, crystallized once more, has mp 219.0-220.6° [a][, 36° (acetone), reported mp 220° [aJu 38°. 

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). 

A solution of 1 g of the ethyleneketal of the trione in 40 ml of methanol is treated with 0.2 g of sodium borohydride and the mixture is stirred at 20° for 2 hr. Slow drop wise addition of water precipitates the reaction product as crystals. These are filtered, washed with water and dried, to give 1.02 g of hydroxy ketone, which after crystallization from methylene dichloride-hexane has mp 182-184° (reported 184-186°) -23° (CHCI3). 

To a mixture of ethyl 5a-cholestan-3-one 2a-xanthate (2 g, 3.95 mmol) and 100 ml methanol is added sufficient ether to completely dissolve the solids. Sodium borohydride (90 mg, 2.36 mmol) is added directly to the reaction flask and the solution is stirred at room temperature for 4 hr. (The use of an excess of sodium borohydride and an extended reaction time produces 5oc-cholestan-2a,3a-thiirane.) The reaction is diluted with 200 ml ether and washed several times with ca. 100 ml water, dried (MgS04) and the solvent is removed under vacuum. The crude sticky gum is chromatographed on a column of 85 g silicic acid. The hexane eluates contain 5a-cholest-2-ene. Ethyl 5a-cholestan-3a-ol 2a-xanthate is obtained in ca. 30% yield by subsequent elution with benzene hexane (1 7) and the desired ethyl 5a-cholestan-3 -ol 2a-xanthate is eluted with ether hexane (1 3) in ca. 30% yield. 

A solution of 24.6 g of o-allyl-epoxypropoxybenzene dissolved in 250 ml of absolute ethanol saturated with ammonia was placed in an autoclave and heated on a steam-bath for 2 hours. The alcohol was then removed by distillation and the residue was redissolved in a mixture of methanol and ethylacetate. Hydrogen chloride gas was introduced into the solution. The hydrochloride salt was then precipitated by the addition of ether to yield 11.4 g of product. Five grams of the amine-hydrochloride thus formed were dissolved in 50 ml of methanol and 9 ml of acetone. The resulting solution was cooled to about 0°C. At this temperature 5 g of sodium borohydride were added over a period of 1 hour. Another 2.2 ml of acetone and O.B g of sodium borohydride were added and the solution was kept at room temperature for 1 hour, after which 150 ml of water were added to the solution. The solution was then extracted with three 100-ml portions of ether which were combined, dried over potassium carbonate, and evaporated. The free base was then recrystallized from petrol ether (boiling range 40°-60°C) to yield 2.7 g of material having a melting point of 57°C. 

D) Preparation of 2-(1-Hydroxyethyi)-3-Methyi-5-(2-Oxo-2,5-Dihydro-4-Furyi)Benzo[b] Furan (3574 CB) 13,2 grams of compound 3556 CB of which the preparation is described in (C) are treated successively with 66 ml of methylene chloride, 27 ml of methanol and, with stirring, 1.6 grams of sodium borohydride added in stages. The reaciton takes 1 hour. The mixture is poured into water acidified with a sufficient amount of acetic acid, the solvents are stripped under vacuum, the crystalline product removed, washed with water, and recrystallized from ethyl acetate. Yield 90%. MP <=158°C. 

A solution of 400 g of oj-bromo-o-chloroacetophenone in one liter of methanol was cooled to about 25 C. A cold solution of 92.5 g of sodium borohydride in one liter of methanol was added as rapidly as possible to this cooled solution while maintaining the temperature... 

Stage 4 Preparation of 1-l2-Phenyi-2-Methoxyl -Ethyi-4-[3-Phenyl-3-Hydroxypropyl] -Piperazine Dihydrochioride - In a double-neck flask equipped with a thermometer and a mechanical stirrer, there is placed in suspension in 800 ml of methanol, 233 grams of 1-[2-phenyl-2-methoxy]-ethyl-4-[2-benzoyl-ethyl]-piperazine dihydrochioride (0.55 mol). It is cooled to approximately 5°C, and 46 grams of NaOH pellets dissolved in 80 ml of HjO are added. When the temperature is about 5°C, one addition of 29,2 grams of sodium borohydride in 40 ml HjO is made. The ice-bath is then removed and stirring continued at ambient temperature for 6 hours. 

To a solution of 3.0 g of the enol-ether compound obtained above in 50 ml of methanol, is added 1.5 g of sodium borohydride. After standing for 1 S hours at room temperature, the reaction solution is poured into 300 ml of water. The resulting precipitates are collected by filtration and recrystallized from ether to give 2.8 g of 3-ethoxy-18/3-ethylestra-3,5-dien-17/3-01 melting at 131°C to 133°C. 

A solution of sodium borohydride (8 grams) in water (16 ml) was added to a stirred solution of 2(3,16(3-bis-piperidino-5a-androstan-3a-ol-17-one (17 grams) in tetrahydrofuran (70 ml) and methanol (30 ml) and the solution stirred at room temperature for 16 hours. The product was precipitated by the addition of water, filtered off, dried, and crystallized from acetone to give the diol (14.9 grams). 

Crude crystals of 3-(2-methylthio-2-piperidinoacetyl -5-phenylisoxazole (1.631 g) are suspended in 20 ml of methanol without being further purified and the suspension is stirred after a portionwise addition (in about 10 minutes) of 143 mg (3.7B mmol) of sodium borohydride at room temperature for about 30 minutes. 

A solution of 1.0 g of 3,17-androstandione in 50 ml of methanol and containing 1 g of selenium dioxide, was allowed to remain in an ice-chest overnight. The formed 3,3-dimethoxy-androstan-17-one was not separated. 1 g of solid potassium hydroxide and 2.5 g of sodium borohydride in 2.5 ml of water were added and the mixture allowed to react at room temperature for 24 hours. The solution was then poured into a large excess of water, extracted... 

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