Sodium borohydride complexes, dimethyl

A boron analog - sodium borohydride - was prepared by reaction of sodium hydride with trimethyl borate [84 or with sodium fluoroborate and hydrogen [55], and gives, on treatment with boron trifluoride or aluminum chloride, borane (diborane) [86. Borane is a strong Lewis acid and forms complexes with many Lewis bases. Some of them, such as complexes with dimethyl sulfide, trimethyl amine and others, are sufficiently stable to have been made commercially available. Some others should be handled with precautions. A spontaneous explosion of a molar solution of borane in tetrahydrofuran stored at less than 15° out of direct sunlight has been reported [87]. 

High yields of amines have also been obtained by reduction of amides with an excess of magnesium aluminum hydride (yield 100%) [577], with lithium trimethoxyaluminohydride at 25° (yield 83%) [94] with sodium bis(2-methoxy-ethoxy)aluminum hydride at 80° (yield 84.5%) [544], with alane in tetra-hydrofuran at 0-25° (isolated yields 46-93%) [994, 1117], with sodium boro-hydride and triethoxyoxonium fluoroborates at room temperature (yields 81-94%) [1121], with sodium borohydride in the presence of acetic or trifluoroacetic acid on refluxing (yields 20-92.5%) [1118], with borane in tetrahydrofuran on refluxing (isolated yields 79-84%) [1119], with borane-dimethyl sulflde complex (5 mol) in tetrahydrofuran on refluxing (isolated yields 37-89%) [1064], and by electrolysis in dilute sulfuric acid at 5° using a lead cathode (yields 63-76%) [1120]. 

Reduction of 5,5-dimethyl-2-pyrrolidone with 3 mol of lithium aluminum hydride by refluxing for 8 hours in tetrahydrofuran gave 2,2-dimethylpyrrol-idine in 67-79% yields [1123]. Reduction of e-caprolactam was accomplished by heating with sodium bis(2-methoxyethoxy)aluminum hydride [544], by successive treatment with triethyloxonium fiuoroborate and sodium borohydride [1121], and by refluxing with borane-d ras. )a.y sulfide complex [1064]. 

Complex hydrides were used for reductions of organometallic compounds with good results. Trimethyllead chloride was reduced with lithium aluminum hydride in dimethyl ether at —78° to trimethylplumbane in 95% yield [1174, and 2-methoxycyclohexylmercury chloride with sodium borohydride in 0.5 n sodium hydroxide to methyl cyclohexyl ether in 86% yield [1175]. 

Any of these BH3 compounds adds readily to most alkenes at room temperature or lower temperatures. The reactions usually are carried out in ether solvents, although hydrocarbon solvents can be used with the borane-dimethyl sulfide complex. When diborane is the reagent, it can be generated either in situ or externally through the reaction of boron trifluoride with sodium borohydride ... 

SYNTHESIS A well-stirred solution of 1.77 g 2,5-dimethoxy-B-nitro-4-(n-propylthio)styrene (see under 2C-T-7 for its preparation) in 20 mL anhydrous THF was placed in an He atmosphere and treated with 1.5 mL of 10 M borane-dimethyl sulfide complex. This was followed by the addition of 0.2 g sodium borohydride, and the stirring was continued at room temperature for a week. The volatiles were removed under vacuum, and the residue was treated with 20 mL dilute HC1 and... 

In contrast to lithium aluminum hydride, sodium borohydride does not reduce amides. Another possible reagent would be DIB AH. However, in the present case four equivalents of borane-dimethyl sulfide complex was used as a 2M solution in THE The amine was obtained in 94% yield after workup with ethanol. 

Both mononuclear and binuclear forms of [PtMe2(dppm)] and [PtClMe(dppm)] can be prepared (see Scheme 2). The cis-dimer (XXVII) is the less stable form and is converted to monomeric [PtMe2(dppm)] (XXVIII) when heated in the presence of dimethyl-sulfide. The monomethyl derivatives Complexes XXIX and XXX can be interconverted in solution but Complex XXX is more stable in solution (especially in polar solvents) and is isolated easily as either the chloride or the hexafluorophosphate salt. A binuclear methyl(hydrido) derivative (XXXI) can be prepared by reducing Complex XXX with sodium borohydride. 

Borane, which is used as a complex with tetrahydrofuran [992] or dimethyl sulfide [611, 992] or generated in situ from lithium borohydride with boron trifluoride etherate [646] or sodium borohydride with aluminum chloride [184], reacts with 3 mol of an alkene to form a tertiary borane. The oxidation with alkaline hydrogen peroxide [183, 992, 1201] or with trimethylamine oxide [991, 992] yields an alcohol (equations 598 and 599). 

Thiosaccharin is reduced by the borane-dimethyl sulfide complex to 2,3-dihydro-1,2-benz-isothiazole 1,1-dioxide <90JCR(S)106>. Sodium borohydride reduces 3-substituted 1,2-benzisothiazole... 

Malate esters are easily reduced in a highly selective fashion using either diborane [40,41] or borane—methyl sulfide complex [42— 45] in the presence of a catalytic amount of sodium borohydride (5 mol%) to give diol esters 45. Yields of 45a and 45b generally range from 80-97%, while 45c is formed in 60% yield [46]. Dimethyl (5)-malate is reduced with 99 1 selectivity as regards C-1 to C-4 ester reduction, while diethyl ( S)-malate shows even greater selectivity (200 1). 

One of the most potent frameworks for the synthesis of two contiguous stereochemically defined asymmetric centers is the chiral epoxy functionality. Prepared in molar-scale quantity from dimethyl L-tartrate (la), bromohydrin 860 is a shelf-storable solid that undergoes selective reduction at the a-hydroxy ester function with borane-dimethylsulfide complex in the presence of catalytic sodium borohydride to provide a 4 1 mixture of methyl (2S,3S)-2-bromo-3,4-dihydroxybutanoate (861) and methyl (2i, 3i )-3-bromo-2,4-dihydroxybutanoate (862). Without purification this mixture is treated with ert-butyldimethylsilylchloride and then exposed to sodium methoxide, which results in conversion to the single epoxide methyl (2i, 3iS)-4-( err-butyldimethylsilyloxy)-2,3-epoxybutanoate (863) in 95% yield and with 99% optical purity (Scheme 188). 

Organoboranes are obtained by addition of borane or alkyl boranes to alkenes (or alkynes). Borane itself can be prepared by reaction of boron trifluoride ether-ate with sodium borohydride. Borane exists as a dimer, but solutions containing an electron donor, such as an ether, amine or sulfide, allow adduct formation. The complexes BHa-THF and the borane-dimethyl sulfide complex BH3 SMc2 are commercially available and provide a convenient source of borane. The dimethyl sulfide complex is more stable than BHa-THF and has the additional advantage that it is soluble in a variety of organic solvents, such as diethyl ether and hexane. 

Diborane can be generated in situ from sodium borohydride and boron trifluoride. Solutions in tetrahydrofuran are commercially available. An alternative commercially available reagent is the borane-dimethyl sulfide complex ... 

Hydride reagents such as lithium aluminum hydride, sodium borohydride, 394-398] dimethyl sulfide complex can be efficiently employed for a highly... 

Olefinic aldehydes have been synthesized by a variety of methods including oxidation of the corresponding primary alcohols with the chromium trioxide-pyridine complex 195—197) or N-chlorosuccinimide-dimethyl sulfide complex 198), heating a primary alken-l-yl mesylate with dimethylsulfoxide 199), or by alkylation of the lithium salt of 5,6-dihydro-2,4,4,6-tetramethyl-l,3-(4H)-oxazine with an alkynyl iodide followed by sodium borohydride reduction and acid hydrolysis (200). 

A previous report that 3-bromothiochroman-4-one is reduced by sodium borohydride to the cis-3-bromo-4-hydroxy-compound has been confirmed. Attempts to methylate 3-methylthiochroman-4-one with methyl iodide-potassium t-butoxide failed to produce the expected 3,3-dimethyl derivative instead, the much more complex product (49) is formed. Methylation with other bases present, however, does proceed normally. 

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