Halides, aryl reaction with lithium

The aryl- and alkyllithiums can be prepared from the corresponding halides by reaction with lithium metal. A mole of lithium halide is produced as a by-product... 

Organocadmium compounds can be prepared from Grignard reagents or organo-lithium compounds by reaction with Cd(II) salts.180 They can also be prepared directly from alkyl, benzyl, and aryl halides by reaction with highly reactive cadmium metal generated by reduction of Cd(II) salts.181... 

The next series of fully-conjugated indeno[l,2-b]fluorenes synthesized by Haley et al. was 6,12-diarylindeno[l,2-b]fluorenes (Scheme 26) [77]. Similar to 96a-i, lithium-halogen exchange with the appropriate aryl halide and reaction with 22 afforded mixtures of stereoisomers 97a-i. Reduction using anhydrous SnCl2 at elevated temperatures provided 87a-j in 36-59% yield. The electron-withdrawing... 

In that vein, it has been subsequently shown (by reactions which most probably involve a series of one electron transfer processes) that halogens can be stripped from almost any alkyl, alkenyl, or aryl halide by treatment with lithium (Li) or sodium (Na) in the presence of a proton donor such as (commonly used) 2-methyl-2-propanol (r-butanol [(CH3)3C-OH], r-BuOH). A solvent such as oxacyclopentane (THE) helps to moderate the reaction. Rearrangements of the carbon skeleton are common. Because it usually lacks selectivity, the method is only rarely used (unless the goal is destruction of the halogenated compound). 

Aryl sulfides are prepared by the reaction of aryl halides with thiols and thiophenol in DMSO[675,676] or by the use of phase-transfer catalysis[677]. The alkenyl sulfide 803 is obtained by the reaction of lithium phenyl sulfide (802) with an alkenyl bromide[678]. 

A key step in the reaction mechanism appears to be nucleophilic attack on the alkyl halide by the negatively charged copper atom but the details of the mechanism are not well understood Indeed there is probably more than one mechanism by which cuprates react with organic halogen compounds Vinyl halides and aryl halides are known to be very unreactive toward nucleophilic attack yet react with lithium dialkylcuprates... 

Formation of aryl Grignard reagents (Section 14 4) Aryl halides react with magnesium to form the corresponding arylmagnesium halide Aryl iodides are the most reac tive aryl fluorides the least A similar reaction occurs with lithium to give aryllithium reagents (Section 14 3)... 

Preparation Using Metallic Lithium. Most simple organolithium reagents can be prepared by reaction of an appropriate halide with lithium metal. The method is applicable to alkyl, aryl, and alkenyl lithium reagents. 

Sn2 and SN2 Reactions with Halides and Sulfonates. Corey and Posner discovered that lithium dimethylcuprate can replace iodine or bromine by methyl in a wide variety of compounds, including aryl, alkenyl, and alkyl derivatives. This halogen displacement reaction is more general and gives higher yields than displacements with... 

Hindered lithium dialkylamides can generate aryl-substituted carbenes from benzyl halides.162 Reaction of a,a-dichlorotoluene or a,a-dibromotoluene with potassium r-butoxide in the presence of 18-crown-6 generates the corresponding a-halophenylcarbene.163 The relative reactivity data for carbenes generated under these latter conditions suggest that they are free. The potassium cation would be expected to be strongly solvated by the crown ether and it is evidently not involved in the carbene-generating step. 

Similarly to the alkyl derivatives, the most common route for arylcopper compounds is the reaction of a copper halide and aryllithium compounds (Equation (4)). Organocuprates with aryl groups are obtained by using an appropriate excess of the lithium reagent. Magnesium aryls have also been employed in transmetallation reactions with Cu(l) salts to yield both arylcopper compounds and arylcuprates (Equations (5) and (6)). 

Several organolithium compounds have important apphcations in organic syntheses. These may be readily synthesized by reactions of lithium with organics. The metal reacts with alkyl or aryl halides or mercury alkyls or aryls to produce alkyl or aryl hthium. Some examples are ... 

Acyl halides can be reduced to aldehydes1206 by treatment with lithium tri-f-butoxyaluminum hydride in diglyme at -78°C,1207 R may be alkyl or aryl and may contain many types of substituents, including N02, CN, and EtOOC groups. The reaction stops at the aldehyde stage because steric hindrance prevents further reduction under these conditions. Acyl halides can also be reduced to aldehydes by hydrogenolysis with palladium-on-barium sulfate... 

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