Alkyl Halides to Olefines

A reaction sequence starting with bistphenyltelluro]methane leads, via an alkyl phenyl tellurium oxide, to a terminal olefin. The olefin has one more carbon atom than the alkyl halide used to prepare the phenyl alkyl tellurium.  

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Free-radical addition of alkyl halides to olefins... 

Besides the addition of such reagents as halogens, hydrogen halides, or the hypohalous acids, there are other reactions which appear to proceed through addition mechanisms, but the exact course of the process is sometimes considerably obscured. The Friedel-Crafts addition of alkyl halides to olefins (p. 145), the self-condensation of olefins, and the alkylation of isoparaffins are examples in which attack at the double bond seems to be led by a carbonium ion. 

Triphenylphosphine reacts with alkyl halides to form alkyltriphenylphosphonium salts. Upon reaction with strong bases, the salts release a proton to form an ylide (alkylidenetriphenylphosphorane), which is capable of reacting with aldehydes or ketones providing an unambiguous route to olefins. Since there are virtually no... 

Ferrocene behaves in many respects like an aromatic electron-rich organic compound which is activated toward electrophilic reactions.In Friedel-Crafts type acylation of aromatic compounds with acyl halides, ferrocene is lO times more reactive than benzene and gives yields over 80%. However, ferrocene is different from benzene in respect to reactivity and yields in the Friedel-Crafts alkylation with alkyl halides or olefins. The yields of ferrocene alkylation are often very low. and the separations of the polysubstituted byproducts are tedious. 

It would be inappropriate, and indeed superfluous, to review here the whole of this very complicated field, since this has been done adequately by several authors [2, 4-7]. For our present purposes we need to pick out only one other aspect, that of co-initiation by alkyl halides. It was proved that with certain olefins and metal halides the addition of an alkyl halide to a mixture of metal halide and olefin would initiate polymerisation [8], and this was interpreted by an extension of the theory of co-initiation, in terms of the reaction scheme (2) ... 

Nucleophilic Reactions.—Attack on Saturated Carbon. Selected examples of the Arbusov reaction include phosphorylation of the chloroacetophenones (1) to give phosphonates, which cyclized to (2) in the presence of acid chlorides,1 formation of the azodiphosphonate (3) from 2,2 -dichloro-2,2 -azopropane,2 3 and the reaction of 2-chloro-3,4-dihydro-3-oxo-2//-l,4-benzothiazine (4) with triethyl phosphite to give the 2-phosphonate (5), which is used as an olefin synthon.8 Bis(trimethylsilyl) trimethylsiloxymethylphosphonite (6) has been synthesized by silylation of hydroxy-methylphosphonous acid, and, as expected, undergoes a normal Arbusov reaction with alkyl halides to give the phosphonates (7).4 This series of reactions, followed by... 

Tertiary amines do not react with nitrous acid, acetyl chloride, benzoyl chloride, benzenesulfonyl chloride, but react with alkyl halides to form quaternary ammonium halides, which are converted by silver hydroxide to quaternary ammonium hydroxides. Quaternary ammonium hydroxides upon heating yield (1) tertiary amine pins alcohol (or, for higher members, olefin plus water). Tertiary amines may also be formed (2) by alkylation of secondary amines, e.g., by dimethyl sulfate, (3) from amino acids by living organisms, e g, decomposition of fish in the case of trimethylamine. 

Ionic liquids are also being evaluated as alternatives to the use of hydrofluoric acid and sulfuric acid—for example, in simplifying aromatic alkylations by directly using olefins instead of alkyl halides to carry out the alkylation. 

Intramolecular photoalkylation of a C=C bond occurs in citronellyl iodide (equation 14)66. The percentage of cyclization is enhanced at the expense of elimination by the presence of CuCl, possibly due to a template effect. CuCl also promotes the very inefficient photochemical addition of simple alkyl halides to to olefins, and does especially so as CuC1- -Bu3P complex67. 

There are quite a number of routes available for the production of iridium(ni) alkyl compounds. In addition to the halide displacement and olefin insertion pathways noted above for iridium(l) compounds, oxidative addition of C-H bonds to iridium(l) to form iridium(in) hydrido alkyl complexes is also a possibihty. This subject will be covered in detail in Section 9 and will not be discussed here. However, there are other oxidative addition routes that lead to the formation of iridium(lll) alkyls. First, oxidative addition of O2 or HCl to some alkyl and aryl iridium(l) complexes can produce iridium(lll) alkyl or aryl compounds. In some cases, HgCl2 can add, but this appears to lead to tractable products only for the very stable pentafluorophenyl complex. Of course, oxidative addition see Oxidative Addition) of alkyl halides such as H3CI will also yield alkyl iridium(lll) compounds. Addition of Mel to Vaska s compound yields a stable iridium(III) complex, but addition of Etl does not produce a stable compound, presumably due to subsequent /J-hydride elimination see fi-Hydride Elimination). A number of mechanistic studies have been done on the oxidative addition of alkyl halides to iridium(l), especially Vaska s complex see Vaska s Complex). 

Alkyl phenyl telluriums react with AT-chloro-A-sodio-4-methylbenzenesulfonamide in refluxing THF to yield terminal olefins from prim, alkyl groups and a mixture of 1 -alkenes and 2-alkenes from sec. alkyl groups. Diorgano tellurium imides were postulated as intermediates. Considering the synthesis of the alkyl phenyl tellurium from an alkyl halide and benzenetellurolate, the overall reaction is the conversion of an alkyl halide to an olefin. Starting with lithiomethyl phenyl tellurium and an alkyl halide, the resulting olefin will have one carbon atom more than the alkyl halide. ... 

In the Zr-catalyzed enantioselective alkylation reactions discussed above, we discussed transformations that involve the addition of alkylmagnesium halides and alkylaluminum reagents to olefins. With the exception of studies carried out by Negishi and coworkers, all other processes involve the reaction of a C-C n system that is adjacent to a C-0 bond. Also with the exception of the Negishi study [Eqs. (6) and (7)], where direct olefin carbometallation occurs, all enantioselective alkylations involve the intermediacy of a metallacyclopentane (cf. Scheme 3). In this segment of our discussion, we will examine the Ni-catalyzed addition of hard nucleophiles (e.g., alkylmagnesium halides) to olefins that bear a neighboring C-0 unit. These reactions transpire by neither of the above two mechanistic manifolds (metallacyclopentane intermediacy or direct carbometallation). Rather, these processes take place via a Ni-Ti-allyl complex. 

In protic solvent at neutral to slightly acidic pH, hydridocobaltflll) species react with alkyl halides to give alkyl Co(III) species at a compatible rate to the corresponding Co(I) complex . The stereochemistry of addition to olefins and alkynes changes as the... 

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

The consecutive addition of alkyl halide to activated olefins by photoelectrocatalysis (PEC) of hydroxocobalamin hydrochloride allows the construction of extended carbon chains as shown for the synthesis of pheromone queen substance 9. The mild conditions of the B12/PEC reaction are suited for the addition of primary alkyl halides 10 containing a potential leaving group. This is illustrated in the synthesis of endo- and exo-brevicomin (11) (Scheme 4). 

Secondary and tertiary alkyl halides give olefins on occasions,223 and / -un-saturated alkyl halides give products of allylic rearrangement.224 -Dibromo-alkanes give bisphosphonium salts in satisfactory to high yield.225 Unlike di-bromomethane, tribromomethane reacts with triphenylphosphine only to the monoquaternary salt stage, the reaction being radical jin nature.226... 

Preparation of Alkyl Halides from Olefins. There are two general methods for the synthesis of alkyl halides (1) by the interaction of an alcohol with a halogen hydride—a procedure that may reasonably be discussed under esterification or halogenation and, also, under the Friedel-Crafts synthesis when a metal halide is used to catalyze the reactions— and (2) by the addition of a halogen hydride to an unsaturated hydrocarbon. This reaction may be catalyzed by metal halides and by sulfuric acid. In the latter instance, the ethylsulfuric acid first formed is converted to the halide by gaseous chlorine or chlorine liberated in situ by action of sulfuric acid on a halide. 

In general, the ease of synthesis of alkyl halides from olefins is dependent on the molecular weights of the hydrocarbons and the particular hydrogen halide. Thus, as was explained earlier in this chapter, the reaction becomes more difficult in passing from iodides through bromides to chlorides. Likewise, olefins containing several carbon atoms react much more readily than those of a lower order. 

The Group VIB arene-metal tricarbonyl complexes are effective homogeneous catalysts for the dehydrohalogenation of aliphatic alkyl halides to create an olefin function [17]. Often mixtures of several isomers occur in these reactions with terminal alkenes being formed as the major product (Scheme 5). This suggests that the proportion of products depends on their relative rate of formation (kinetic control). 

The same OEP dimer and its TpTP analog are obtained by photolysis of the hydride derivatives . The reaction of [Rh(OEP)]2 with alkyl halides, unactivated olefins, and acetylenes gives the o-bonded metal-carbon derivatives according to Scheme 15 . ... 

Phosphine readily adds to a-olefins in the presence of a free-radical initiator to yield tertiary alkylphosphines quantitatively [11]. Although these tertiary alkylphosphines have pfQs which are typically an order of magnitude lower than their amine counterparts and consequently are less basic, the more poIari2able lone pair makes them much more nucleophilic than the corresponding amines [12,13]. As a result, tertiary alkylphosphines readily undergo nucleophilic addition to a variety of alkyl halides to yield tetraaUcylphosphonium salts [13]. 

Numerous studies confirm the need by many Lewis acids for other molecules, like water or alkyl halides, to form initiating ions. For instance, pure TICU will not initiate the polymerization of isobutylene. This led many to believe that none of the Lewis acids is capable of initiating cationic polymerizations of olefins by itself. Subsequent investigations, however, demonstrated " that some strong Lewis acids are capable of initiating such polymerizations. 

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