Alkyl halides to alkanes

Alkyl phenyl telluriums, obtained from alkyl halides and arenetellurolates, are reduced by triphenyl tin hydride to alkanes under mild conditions The alkanes were obtained in yields ranging from 71 to 95%. 5a-Cholestan-3a-yl phenyl tellurium was similarly reduced to 5a-cholestane in 89% yield. The reaction appears to be highly chemoselective as indicated by the reduction of an epoxide to an alcohol in the presence of a carbonyl group.  

5-Dihydrobenzo[c]tellurophene and 2,5-dihydronaphtho[2,3-c]tellurophene, obtained from the l,2-[bromomethyl]arenes and sodium telluride, when heated at 500° in an atmosphere of helium extruded tellurium and formed cyclobutenes in good yields.  

9-Tellurabicyclo[3.3.l]nona-2,6-diene, prepared from sodium telluride and 1,5-dibromoocta-2,6-diene, lost tellurium when heated at 175° in toluene in a sealed tube giving bicyclo[5.1.0]octa-2,5-diene b 

Diallyl tellurium, obtained from allyl bromide and sodium telluride, decomposed at 180° with formation of biallyl (1,5-hexadiene).  

The organic groups in diorgano telluriums coupled when the tellurium compounds were refluxed in acetonitrile in the presence of a stoichiometric amount of palladium prepared in situ from palladium(II) acetate.  

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Reduction of simple alkyl halides to alkanes by ethylenediamine complexes of Cr(II), denoted Cr"(en) occurs readily , e.g. for isopropyl chloride in aqueous dimethylformamide at 25 °C simple second-order behaviour is found with ki dependent on [en]/[Cr(II)] but reaching a limiting value of 1.6x 10 l.mole . sec . Competition studies between a mixture of two alkyl chlorides for Cr(II) was achieved by estimating alkane products by gas-liquid chromatography and... 

As noted earlier, [HCr(CO)5] also converts alkyl halides to alkanes, but the reactivity of the acyl chloride is much higher, such that it was possible to selectively convert the acyl chloride to an aldehyde in one step, without interference from the alkyl bromide functionality. A second equivalent of [HCr(CO)5] further reduced the alkyl bromide (Eq. (27)). 

Lithium aluminium hydride (LiAlH4), a strong reducing agent, reduces alkyl halides to alkanes. Essentially, a hydride ion (H ) acts as a nucleophile displacing the halide. A combination of metal and acid, usually Zn with acetic acid (AcOH), can also he used to reduce alkyl halides to alkanes. 

Tetra-p,3-carbonyldodecacarbonylhexa-rhodium, 288 of alkyl halides to alkanes Chromium(II) chloride, 84 Lithium aluminum hydride-Ceri-um(III) chloride, 159... 

Reduction reactions, of alkyl halides to alkanes (Continued)... 

T. Imamoto, Reduction of Saturated Alkyl Halides to Alkanes, in Comprehensive Organic Synthesis (B. M. Trost, I. Fleming, Eds.), Vol. 8, 793, Pergamon Press, Oxford, U. K., 1991. 

In the presence of a radical initiator (Z-), tributyltin hydride (RgSnH, R = CH3CH2CH2CH2) reduces alkyl halides to alkanes R X + RgSnH -> R H + RgSnX. The mechanism consists of a radical chain process with an intermediate tin radical ... 

The reduction of saturated alkyl halides to alkanes, as represented in equation (1), is the most fundamental reaction of reductive dehalogenations of organic halides. The importance of these reductions has stimulated considerable investigation, and a number of successful approaches have been reported hitherto. Numerous reducing agents or reagent systems are available and many of them have been applied to practical organic synthesis with notable success. 

This chapter surveys the reduction of saturated alkyl halides to alkanes. Reductive -eliminations of vicinal dihalides to alkenes are also described briefly. Reduction of vinyl and aryl halides is covered in this volume. Chapter 4.5 hydrogenolysis of allyl and benzyl halides is covered in this volume. Chapter 4.7, and reduction of a-halo-substituted carbonyl compounds CX—CO to carbonyl compounds CH—CO is covered in this volume. Chapter 4.8. 

CrCI2 reduction of alkyl halides to alkanes, of acetylenes to trans olefins, of epoxides to olefins, or of nitro compounds to oximes. 

Similar reactivity towards activated methyl compounds, especially methyl iodide, has been observed for Ni OEiBC [114, 115, 61, 116] and for Ni (tmtaa) (where tmtaa is the dianion of 6,8,15,17-tetramethyl-5,14-dihydro-dibenzo [b,i] [1, 4, 8, ll]tetraazacyclotetradecine) [112, 113]. Ni tmtaa), generated in situ by reduction of Nin(tmtaa) and observed by EPR, was proposed as the active catalyst in the reduction by NaBH4 of alkyl halides to alkanes. Recently, a different Ni(I) tetraazamacrocyclic complex, produced by irradiation of the Ni(II) parent compound with 5 MeV electrons, produced small amounts of methane from subsequently added CH3S-CoM [111]. The represented the first report of reactivity of any identifiably Ni(I) species with the natural substrate. 

Reactions.—New systems for the reduction of alkyl halides to alkanes include mixtures of lithium aluminium hydride with transition-metal chlorides (such as Ni or Co" chlorides) and some complex metal hydrides of copper, especially the THF-soluble Li4CuHs. Details of the application of sodium cyanoborohydride to the reduction of halides (and sulphonate esters) in dipolar aprotic solvents have been published. Virtually all other functional groups are inert to this convenient, mild, and efficient system, which has been used to develop a one-pot deoxygenation of primary alcohols (Scheme 39) via the iodides. The alternative cyanoborohydride reagents (55) and the polymeric (56) are also discussed. ... 

A variety of metal hydrides reduce alkyl halides to alkanes. Sodium borohydride has been extensively used in aprotic solvents like DMSO, DMF, diglyme and sulpholane. Reduction with this hydride in the presence of phase transfer catalysts is even more advantageous. Sodium borohydride in the presence of nickel boride (Ni2B) has been... 

Several organometallic reagents have surfaced in recent years for the reduction of the carbon-halogen bond. A titanocene dichloride-magnesium system reduces alkyl halides to alkanes under mild conditions and in good yield (equation 52) . New reagents based on 9-borabicyclo[3.3.1]nonane ( 9-BBN ) ate complexes have been used for the efficient reduction of tertiary halides (equation 53) ... 

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