Reduction of halides

The reactions are commonly initiated with AIBN at ca. 80 °C in a solvent such as benzene or toluene, but alkyl halides have also been reduced at -60 °C with tributyltin hydride under sonication conditions.133-134 Some reductions of halides have been carried out by generating the tin hydride in situ from a molar equivalent of the reducing agent [lithium aluminium hydride, sodium borohydride, or poly(methylhydrosiloxane)] and a catalytic amount of organotin hydride, halide, or oxide. Reduction of halides has also been carried out under aqueous conditions, using 4,4 -azobis(4-cyanovaleric acid) (ACVA) as a water-soluble radical initiator.60 

Examples of halide reductions are given in equations 15-40,135 15-41,136 15-42,137 15-43,68 15-44.138 It will be noted that in reaction 15-41, an acetoxyl group is migrating in the intermediate radical. 

If halides RX are reduced in the presence of carbon monoxide, the free radical is carbonylated to the acyl radical, and the product is the aldehyde RCH=0 (equation 15-45),139 141 and if the reduction is carried out with NaBH3CN in the presence of a catalytic amount of the tin hydride, the alcohol RCH2OH can be prepared directly.142 

An interesting recent development is the demonstration that the reactivity of a stannyl radical can be controlled by amines that act intra- or inter-molecularly as ligands for the tin. Thus the stannyl radicals that are derived from dibutyl-2(2-pyridylethyl)tin hydride and butylbis-2(2-pyridylethyl)tin hydride show a reduced reactivity towards alkyl bromides and chlorides, and the presence of bipyridyl effectively suppresses the reduction of C12H25CI by Bu3SnH.56 

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This section lists the reductions of halides and sulfonates, R-X R-H. 

Germyl, Stannyl, and Plumbyl Anions The preparative methods for the synthesis of the germyl, stannyl, and plumbyl anions are essentially the same as those mentioned above for the silyl anions. The most widely used methods are (1) reduction of halides R3EX (R = alkyl, aryl E = Ge, Sn, Pb X = Cl, Br) with alkali metals and (2) reductive cleavage of the E-E bond of R3E-ER3 (R = alkyl, aryl E = Ge, Sn, Pb) with alkali metals or organolithium reagents. Due to the favorable polarization of the (E = Ge, Sn, Pb) bond, the direct metalation... 

The presence of transition metal ions has a catalytic effect on reduction of halides and tosylates by LiAlH4.166 Various copper hydride reducing agents are effective for removal of halide and tosylate groups.167 The primary synthetic value of these reductions is for the removal of a hydroxy function after conversion to a halide or tosylate. 

Electron affinity or reduction of halide radical to halide anion (A )... 

The use of Zn powder in a multiphase system is a way to solve many of the difficulties involved in the operation of electroorganic processes under a low maximum current density [513-516]. A three-phase system, water/organic, substrate/metal powder can be used for the reduction of halides and nitro compounds under a high... 

Actinide (An) metals are prepared by reduction or thermal dissociation of their com-pounds The metallothermic reduction of halides is still in use, especially for microscale preparations. In this procedure, anhydrous actinide haUdes, in general fluorides, are exposed to the vapour of alkaline or alkaUne earth metals, e.g. 

Dehalogenation. Barton et at. (1, 148) effected dehalogenation of steroidal /i-hydroxy halides with chromium(II) acetate and butancthiol as the proton donor in DMSO. The method is only useful with tertiary halides. A recent improvement that permits reduction of halides of all types uses the ethylenediamine complex of CrtCIOzh and the tetrahydropyranyl ethers of the /J-hydroxy halide. Catalytic amounts of the reducing agent can be used in "indirect electrolysis." The reaction is convenient for preparation of deoxynucleosides.1... 

Reduction. Reduction of halides using hydrogen—hydrocarbon mixtures is sometimes done in the presence of a graphite carrier or using metals possessing high melting points, ie, the van Arkel gas deposition method (4). If a plasma gun is employed, finely powdered (< 1 /im) carbides are obtained... 

Reduction of halides (X) with zinc and hydrochloric acid. bles carbon and tin resembles silicon Germanium resem-... 

Reduction of halides.1 The reagent prepared from NaBH3CN and SnCl2 in a 2 1 ratio does not reduce primary or secondary alkyl halides or aryl halides in ether at 25°, but does reduce tertiary, allyl, and benzyl halides. It is thus comparable to NaBH3CN-ZnCl2 (12, 446). Aldehydes, ketones, and acid chlorides are reduced to alcohols, but esters and amides are inert. 

Tris(trimethylsilyl)silane is found to be an efficient reducing agent for a variety of functional groups. In particular, the reduction of halides, chalcogen groups, thiono esters and isocyanides are the most common ones. The efficiency of these reactions is also supported by available kinetic data. The rate constants for the reaction of (TMS)3Si radicals with a variety of organic substrates are collected in Table 2. 

Reduction of halides and sulfonates.2 Sodium borohydride effects this reaction under phase-transfer conditions (aqueous C6H5CH3 or CH2C12). The more lipophilic salts hexadecyltributylphosphonium bromide or tetraoctylammonium bromide are the most effective catalysts. 

Selective reduction of halides.1 Thecomplexl reduces tertiary halides to alkanes without attack on primary or secondary halides. It is more selective than organotin hydrides. Benzylic and allyl halides are also reduced easily. The reagent reduces a mixture of the halides 2 mainly to trims-3 thus, a partial inversion oftonfiguration is... 

Stereoselective radical reductions of halides.1 This hydride when exposed to... 

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