Benzylic halides sodium borohydride

Displacement of bromine on phenacyl halide with imidazole gives Reduction with sodium borohydride followed by displacement with 2,6-dichloro-benzyl alcohol in HMPA then produces antifungal orconazole (37). ... 

The difference in the reactivity of benzylic versus aromatic halogens makes it possible to reduce the former ones preferentially. Lithium aluminum hydride replaced only the benzylic bromine by hydrogen in 2-bromomethyl-3-chloro-naphthalene (yield 75%) [540]. Sodium borohydride in diglyme reduces, as a rule, benzylic halides but not aromatic halides (except for some iodo derivatives) [505, 541]. Lithium aluminum hydride hydrogenolyzes benzyl halides and aryl bromides and iodides. Aryl chlorides and especially fluorides are quite resistant [540,542], However, in polyfluorinated aromatics, because of the very low electron density of the ring, even fluorine was replaced by hydrogen using lithium aluminum hydride [543]. 

Reduction of RCOCI to RCHO. Sodium borohydride and this cadmium salt reduce acyl chlorides to aldehydes, but only in solvents such as DMF, DMA, and HMPT. DMF is essential, but the amount of DMF in the salt is sufficient. For the most part, yields are 50-90%. Aryl, alkyl, and benzylic halides do not react. Other functional groups (nitrile, nitro, ester, C=C) are also inert. 

Arene(tricarbonyl)chromium complexes, 19 Nickel boride, 197 to trans-alkenes Chromium(II) sulfate, 84 of anhydrides to lactones Tetrachlorotris[bis(l,4-diphenyl-phosphine)butane]diruthenium, 288 of aromatic rings Palladium catalysts, 230 Raney nickel, 265 Sodium borohydride-1,3-Dicyano-benzene, 279 of aryl halides to arenes Palladium on carbon, 230 of benzyl ethers to alcohols Palladium catalysts, 230 of carboxylic acids to aldehydes Vilsmeier reagent, 341 of epoxides to alcohols Samarium(II) iodide, 270 Sodium hydride-Sodium /-amyloxide-Nickel(II) chloride, 281 Sodium hydride-Sodium /-amyloxide-Zinc chloride, 281 of esters to alcohols Sodium borohydride, 278 of imines and related compounds Arene(tricarbonyl)chromium complexes, 19... 

A one-pot PTC reaction procedure for the overall conversion of an alkyl halide into a primary amine via an azide is particularly illustrative.204 Thus the reduction of the azide is effected by the addition of sodium borohydride to a reaction mixture arising from the PTC displacement reaction of an alkyl halide with sodium azide (the preparation of 1-octylamine, Expt 5.193). The reaction appears to be applicable to primary and secondary alkyl halides, alkyl methane-sulphonates and benzylic halides. 

A communication and full paper tell of the efficient photoreduction of 4-chlorobiphenyl to biphenyl by excitation of 9,10-dihydro-lO-methylacridine (163) or acriflavine (164) in aqueous acetonitrile containing sodium borohydride. A variety of alkyl halides, benzyl halides and chlorobenzenes were also reduced. The reaction proceeds by electron transfer from the excited state of the dihydroacridine to the chloroarene, chloride loss and hydrogen atom donation to the arene radical. Thus photoreduction of the arene is coupled with oxidation of the dihydroacridine to the acridinium salt the latter is reduced back to the dihydroacridine by the borohydride. 

Thiols and sulfides. Benzylic halides can be converted into either a thiol or a sulfide by reduction with suifurated sodium borohydride depending on conditions of hydrolysis. Aryl halides do not react with the reagent. Aliphatic... 

Silyl and stannyl hydrides effect high yield reduction of aryl diazonium salts, and are compatible with a wider range of solvents than is HaP02. NaH prepared situ has been found to be much more active than the commercial product. Using the more active NaH, hydrogenolysis of benzylic halides is possible. Sodium borohydride has been reported to reduce nitriles to amines if Raney nickel is used as catalyst. 

Methods reported this year for the reduction of alkyl halides to alkanes include the potassium-dicyclohexyl-18-crown-6 reduction of alkyl fluorides, sodium borohydride reduction of alkyl chlorides, bromides, and iodides (or sulphonate esters) under liquid-liquid phase-transfer conditions, and the selective reduction of tertiary alkyl, benzyl, and allyl halides with the borate (61). Continuing... 

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