Reduction alkyl halide

Alkyl Halides. Commonly, reductions with liquid silanes and liquid alkyl halides do not require the use of a solvent.186 When the alkyl halide is a solid, either pentane186 or dichloromethane may be used as solvent.192 No significant difference in reactivities is observed between alkyl chloride and bromide substrates,186 but allyl halides are more reactive than 2-halopropanes, which, in turn, are more reactive than 1-halopropanes.190,146... 

Bromoadamantane and 1-bromoadamantane are reduced to adamantane in yields of 84% and 79%, respectively, when treated with triethylsilane and catalytic amounts of aluminum chloride.186 Similar treatment of benzhydryl chloride and exo-2-bromonorbomane gives the related hydrocarbons in yields of 100% and 96%, respectively.186 In contrast, 2-bromo-l-phenylpropane gives only a 43% yield of 1-phenylpropane the remainder consists of Friedel-Crafts alkylation products.186 Some alkyl halides resist reduction by this method, even when forcing conditions are employed. These include p-nitrobenzyl bromide, 3-bromopropanenitrile, and 5-bromopentanenitrile.186... 

Alkanes can also be prepared from alkyl halides by reduction, directly with Zn and acetic acid (AcOH) (see Section 5.7.14) or via the Grignard reagent formation followed by hydrolytic work-up (see Section 5.7.15). The coupling reaction of alkyl halides with Gilman reagent (R 2CuLi, lithium organocuprates) also produces alkanes (see Section 5.5.2). 

Trialkylaluminums, 21 By geminal alkylation of carbonyl groups Dichlorodimethyltitanium, 216 From reduction of alkyl halides, alkyl sulfonates and similar compounds From acetates or other esters Triphenylsilane, 334 From alcohols... 

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. 

Selective reduction of t-alkyl halides. The ate complex of B-butyl-9-BBN with n-BuLi selectively reduces tertiary alkyl halides to hydrocarbons in high yield without effect on primary or secondary halides. It does not reduce aryl or vinyl halfdes, but does reduce benzyl and allyl halides. The reduction involves a carbonium ion, and thus can proceed with Wagner-Meerwein rearrangements in certain systems. 

Complexes of the type [Rh(TPP)(RX)] [RX = C H X (n = 3-5, X = Cl or Br n = 3-6, X = I) TPP = dianion of tetraphenylporphyrin] were prepared by Anderson et al. (179). The nature of RX was found to determine the overall electrochemical behavior for the reduction of [Rh(TTP)(RX)]. For some complexes, specifically those where X = Br and I, the bound alkyl halide could be reduced without cleavage of the metal-carbon bond. This resulted in the electrochemically initiated conversion of [Rh(TPP)(RX)] to a [Rh(TPP)(R)] complex. The E. value for this reduction was dependent on the chain length and halide of the RX group and followed the trend predicted for alkyl halides. The reduction of the bound RX occured at Ei values significantly less negative that those for reduction of free RX under the same solution conditions. 

The polyHIPE supported thiol is a good catalyst for radical reduction of alkyl halides and reductive cyclisations of e-bromoalkenes by triethylsilane. 

Diborane reacts only slowly with most alkyl halides however, reduction of PhCHjBr occurs readily in PhNOj ... 

Divalent samarium is known to reduce alkyl halides. However, reductions of iodides and bromides in tetrahydrofuran (THF) require a long reaction time and chlorides are not reduced even at refluxing temperature. 

In water, alkyl halides undergo reductive coupling with Mn-CuClj (30 1). In some cases cross-couplings are possible (e.g., 2-methylene-5-hexenolc acid from allyl bromide and bromomethacrylic acid). 

The classical Hofmann elimination reaction (which dates back to 1851) has been adapted to the solid phase in combination with the Michael addition. The REM resin, called this way because the resin tinker is REgenerated after product cleavage and functionalized by means of a Michael addition, has been developed to prepare arrays of tertiary amines. The procedure involves acylation of hydroxy-methylpolystyrene with acrylic chloride to furnish the acrylate on resin. Then, a secondary amine, whose substituents offer two potential sites of diversity, is bound by Michael addition. Quaternization of the amine with an alkyl halide (or reductive animation) introduces another site of diversity and activates the tinker to release the amine by a Hofmann elimination with DIEA (Figure 15.14) [127-129]. Additionally, the use of a second basic resin has been described as a source reagent to promote the elimination [130, 131]. 

Where X is Br or Cl, the free acids may be obtained by acidification of the alkaline solution, but where X is I, the acids must be isolated as salts to avoid reduction of the arsonic acids by HI. Rather than using alkyl halides, alkyl or dialkyl sulfates or alkyl arenesulfonates can be used. Primary alkyl halides react rapidly and smoothly, secondary halides react only slowly, whereas tertiary halides do not give arsonic acids. Allyl halides undergo the Meyer reaction, but vinyl halides do not. Substituted alkyl halides can be used eg, ethylene chlorohydrin gives 2-hydroxyethylarsonic acid [65423-87-2], C2H7As04. Arsinic acids, R sC OH), are also readily prepared by substituting an alkali metal arsonite, RAs(OM)2, for sodium arsenite ... 

Ester- and amide-substituted radicals bearing an adjacent stereocenter abstract hydrogen with high diastereoselectivity1. The radicals are generated via intra- or intermolecular radical addition to alkenes, halogen abstraction from alkyl halides or reductive cleavage of alkylmercury compounds. Some examples are shown in Table 1. 

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