Tetramethylammonium borohydride

From tetramethylammonium chloride and lithium borohydride the thermally stable tetramethylammonium borohydride is produced (4), supporting the hypothesis that a comparable salt is formed intermediately in the reactions of borohydrides with ammonium chloride to give bora-zole (69),... 

Tetramethylammonium acetate, 1142-1143 Tetramethylammonium borohydride, 1143 Tetramethylammonium bromide, 1143 Tetramethylammonium chloride, 962 Tetramethylammonium hydroxide, 468, 1142... 

Tetramethylammonium borohydride, (CH3)4NBH4. Mol. wt. 89.00. Supplier Ventron Corp. 

The o -complexes (H as nucleophile) were prepared by stoichiometric addition of tetramethylammonium borohydride to solutions of nitroarenes in DMF + 0.1 M TBABF4 under inert atmosphere. The electrochemical experiments (cyclic voltammetry and electrolysis) are analogous to those which have been described for 1H (Sect. 2.2). The results are summarized in Table 1. 

Under the protection of nitrogen, the compound 3.6 (332 mg, 1.0 mmol) was dissolved in methanol (10 mL) and tetrahydrofuran (10 mL) and cooled to 0 °C then, tetramethylammonium borohydride (356 mg, 4.0 mmol) was added. The reaction was heated to room temperature and stirred for 24 h. Saturated ammonium chloride solution (10 mL) was slowly added to quench the reaction. The solvent was removed by rotary evaporator and diluted with ethyl acetate (50 mL). The aqueous phase was extracted with ethyl acetate (3 x 50 mL) and washed with saturated brine (20 mL). The combined organic phases were dried over Na2S04 and hltered. Solvent was removed by rotary evaporator. The resulting crude product was purihed by hash silica gel column chromatography (EA/HA = 1 6) to give 274 mg white solid (Rf— 0.50, EA/HA = 1 6), yield 81 %. 46 mg raw material 3.6 was recovered. 

The reduction can be carried out in a distereoselective manner also when the chiral group is in Imposition to the carbonyl. Moreover, a reversal of the sense of the diastereoselectivity can be achieved by the use of diisobutylaluminum hydride (dibal-H) or tetramethylammonium triacetoxy-borohydride (Me4NBH(OAc)3) to give 1,3-jyn or l,3-anti diols, respectively (Scheme 34) <93S903>. 

The thermal decomposition of a variety of tetramethylammonium salts of weak bases has been studied and the major product is generally the methylated anion 92>. The temperature required to decompose the bromide and chloride salts to trimethylamine and the methyl halide is near 360 °C and the products recombine on cooling. The fluoride salt decomposes at a much lower temperature (180 °C) and the products do not recombine 92>. Decomposition of the borohydride salt at 225 °C gives trimethylamine borane and methane 11h... 

The tetramethylammonium tetranitratoborate, formed by reaction of nitrogen dioxide on the corresponding tetrachloroborate (reaction scheme 8), showed a shift of +44 0 p.p.m. from sodium borohydride" ... 

After TBS protection, methanolysis of the dioxolenone liberates the heptanoic acid ester 950. Stereocontrolled reduction of the -keto function furnishes either syn or anti diols depending on the hydride reagent employed. Diethylmethoxyborane-sodium borohydride gives syn-d o 952 as a single isomer in 86% yield, whereas tetramethylammonium triacetoxyborohydride produces a mixture of anti and yw-diols 953 and 952 (ratio anti syn = 10 1) in 85% yield [173] (Scheme 129). 

Diastereoselective Reductions. The diastereoselective reductions of 8-hydroxy ketones could be accomplished with NaBHa in the presence of Et2B(OMe) to form 1,3-syn diols in 68-99% yields and excellent stereochemical purities (dr>98 2) (eq 26). Et2B(OMe) could be generated in situ from Triethylborane and methanol. The method has been successfully utilized in several natural product syntheses and complements the anti-selective reductions performed with Tetramethylammonium Tri-acetoxyborohydride (see also Zinc Borohydride). 

Related Reagents. Cerium(III) Chloride Nickel Boride Potassium Triisopropoxyborohydride Sodium Cyanoboro-hydride Sodium Triacetoxyborohydride Cobalt Boride Lithium Borohydride Lithium Aluminium Hydride Zinc Borohydride Tetramethylammonium Triacetoxyborohydride. 

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