Zinc, reaction with alkyl halides

Frankland s method orgchem Reaction of dialkyl zinc compounds with alkyl halides to form hydrocarbons may be used to form paraffins containing a quaternary carbon atom. frarik-lonz, meth-3d ... 

Monohalogenothiazoles, 567 nucleophilic substitution reactions, 322 with amines. 567 with ArSH, 567 with benzamide, 567 with OH", 567 with OR", 567 relative reactivities, 568 with SR", 567 with sulfinic acid salts, 567 with sulfonamide, 567 reactions, with alkyl halides, 574 with n-butyllithium, 573 with Gtignard reagents, 573 reeduction of, with nickel, 573 with zinc, 573... 

Development of new methodologies for formation of carbon-carbon bonds has been one of the major tasks in organic chemistry. Obviously, organometallic compounds, particularly zinc derivatives, have found great use in such reactions. During the past several years, there have been several significant reports of nickel- and palladium-catalyzed reactions of dialkylzincs and alkylzinc halides with alkyl halides of diverse structure. A detailed account of most of these studies can be found in a recent review by Knochel et al,246... 

Reaction XLI3I. (d) Condensation of Diethyl Oxalate with Alkyl Halides in the presence of Zinc (Frankland- -Duppa). (A., 185, 184.)—This is a type of condensation very similar to those just described. The zinc alkyl is not isolated, and simple halogen compounds are used. The product is a derivative of glycollic acid. 

Anyway, it is doubtful whether Letts and Collie thought about zinc as the catalyst of the reaction of tin with alkyl halides (in spite of their demonstration) since this fact was established considerably later. The authors also found that the reaction of EtI with a Sn—Zn alloy (33-50%) containing 5% of Cu gave a maximum yield of E Sn. Thus, long before Rochows s finding the catalytic influence of copper in the direct synthesis of organometallic compounds was observed636. 

One of the main issues with the use of magnesium and zinc as inexpensive co-reductants is their reactivity with alkyl halides. Also, additives such as TMSOTf are relatively expensive. In an attempt to address these limitations, Namy utilised mischmetal (La 33%, Ce 50%, Nd 12%, Pr 4%, Sm and other lanthanides 1%) as the stoichiometric reductant for the regeneration of the Sm(II).31,32 This reagent system provides an important alternative since it does not require the use of additives and mischmetal is relatively inexpensive. This system has been utilised successfully in Barbier and Reformatsky reactions, halide reductions and pinacol couplings (Scheme 7.7).31,32... 

Direct Reaction of Zn with Alkyl Halides. The direct insertion see Insertion) reaction of Zn metal into alkyl halides - alkyl iodides being the ideal snbstrates - is a nseful reaction to prepare simple or polyfunctional organozinc halide compounds (equation 1). With primary alkyl iodides, the reaction requires an excess of Zn dnst (ca. 3 eqniv), previonsly treated with few mol % of 1,2-dibromoethane and TMSCl, and a temperature of 40 °C in THF. In these conditions, secondary alkyl iodides react at room temperatnre and benzylic and allylic bromides at 0 °C. The insertion see Insertion) into less activated C-X bonds may reqnire more reactive forms of zinc (Riecke zinc), higher temperatures, or the use of polar see Polar Compounds) solvent or cosolvent. 

As a first approximation one can view metallation and electrolytic reduction as a single class of reactions differing only in the ease with which electrons are transferred to the substrate. Ordinarily mercury metal does not react with alkyl halides because of its high ionization potential of 240 kcal mol as compared with 124,176 and 216 kcal mol for lithium, magnesium and zinc, respectively. However, if one places a potential across mercury then it will readily react with alkyl halides in an electrolytic reaction. 

Frankland-Duppa reaction. Formation of a-hydroxycarboxylic esters by reaction of dialkyl oxalates with alkyl halides in the presence of zinc, or amalgamated zinc, and acid. 

Ketones. Rieke zinc produced by the reduction of Zn(CN)j with Li naphthalenide reacts with alkyl halides, and the organozinc halides can be used to form ketones on treatment with CuCN and acid chlorides. Secondary and tertiary alkylzinc bromides are readily prepared in this direct manner." a-Chloromethyl ketones have been prepared by this method using chloroacetyl chloride in the coupling reaction. ... 

Oxidative-addition reactions of alkyl halides also occur with metal ions such as thallium(I). In this case, the HOMO is an s orbital on the metal of a symmetry. The concerted mechanism is now impossible and only a two-step reaction can occur. The same is true for reactions of metals in the free state, such as zinc or magnesium, with alkyl halides. Note that free radicals may be formed, instead of ions, in all cases discussed. Free radical reactions are usually allowed by symmetry. 

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