Metals, activated with alkyl halides

Halides containing longer-chain alkyl groups reacted more slowly. Unalloyed lead metal reacted with alkyl halides, especially if it was oxide free and finely divided (70). Binary alloys of lead with other active metals have also been tried as substrates, with varying success (70). 

Activated bismuth metal reacts with alkyl halides or trifluoromethyl iodide in the presence or absence of metallic copper at high temperatures to afford a mixture of mono- and dihalobismuthines [61JINC213, 63AJC636, 97JA724]. 

Generally, smaller particles are obtained with polar, more highly solvating solvents. However, these solvents do not necessarily yield the most active metal slurries. The reactivities vary, and the metal slurries can be fine tuned somewhat for use in specific types of reactions. For example, nickel particles from pentane are very active as hydrogenation catalysts, whereas nickel particles from THF are not active as hydrogenation catalysts but are very active in alkyl halide reactions. 

Alkylation of Alkali Metal Cyanides by Alkyl Halides Activated in the a-Posi-tion by a Double Bond. When a mixture consisting of 4 to 8 moles of an alkyl halide activated in the apposition by a double bond is heated with 1 mole of alkali metal ferrocyanide, several alkylation products of the ferrocyanide anion can be isolated from the reaction mixture (12). The relative proportions of the tetra-, penta-, and hexaalkylated complexes can be varied by varying the alkyl halide to ferrocyanide ratio and the time of reaction. When potassium ferrocyanide is alkylated with benzyl bromide at a ratio of 4 alkyl halides to ferrocyanide anion, short reaction times favor the tetraalkylated complex an 8 to 1 ratio and long reaction times favor the hexaalkylated complex of the alkylating agents tested benzyl bromide provided the fastest alkylation ... 

In view of the limited stability of the "carbenoid" LiCsCCb Cl, functionalization reactions have to be carried out a temperatures that are as low as possible Silylations of metallated acetylenes are usually rather slow in E12O at temperatures below -20 C. A small amount of HMPT appears to cause a considerable enhancement of the rates of silvlation with trimethylchlorosilane. It is not known whether this effect is only due to the typical properties of HMPT as a dipolar aprorir solvent (also shown in alkylation with alkyl halides) or whether it is a result of active participation of this solvent in the reaction as depicted in the following equations ... 

R2Cd compounds were first obtained by the direct reaction of cadmium metal with alkyl halides. Unfortunately, this method is limited and typically does not readily yield pure products. However, the direct method is facilitated by the use of highly activated cadmium slurries. " ... 

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. 

Reactions of lithium alkyls are generally considered to be carbanionic in nature, but in reactions with alkyl halides free radicals have been detected by electron spin resonance.32 Lithium alkyls are widely employed as stereospecific catalysts for the polymerization of alkenes, notably isoprene, which gives up to 90% of 1,4-cA-polyisoprene numerous other reactions with alkenes have been studied.33 The TMED complexes again are especially active not only will they polymerize ethylene but they will even metallate benzene and aromatic compounds, as well as reacting with hydrogen at 1 atm to give LiH and alkane. 

Organolithium compounds, generally phenyl- or butyllithium, can be used, in the same way as(triphenylmethyl)sodium (see page 917), as base for C-alkyla-tion, since in certain cases they react by metal exchange with activated hydrocarbons. For instance, the 2-lithio derivative of resorcinol dimethyl ether is formed in 70% yield on reaction with phenyllithium. The organolithium compounds thus obtained react readily with alkyl halides or sulfates, forming a carbon-carbon bond 326 for example, 2,6-dimethoxytoluene is formed by... 

The a-alkylation of amines is a valuable synthetic transformation. The amino group itself is not suflBciently activating to allow conversion of an a-methyl (R2N—Me) (or methylene) group into an alkali-metal salt (R2N—CH2—M), but certain derivatives of secondary amines can be converted into lithium salts with a strong base. The resulting a-amino-organolithium species react readily with alkyl halides, aldehydes, acid chlorides and other electrophiles. Successful results have been obtained with A -nitroso derivatives, various sterically hindered amides or for-mamidines. For example, dimethylamine can be converted into the amines 91 and 92 via the formamidine 90 (1.95). ... 

The second pathway is analogous to the reaction of an activated metal, similar to those generated using Riecke s methodology, with alkyl halides. However, Luche reports that pre-activation of the zinc gave poor yields of organozinc under sonochemical conditions. 

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