Organolithium compounds with aryl halides

Organolithium reagents (Section 14 3) Lithi um metal reacts with organic halides to pro duce organolithium compounds The organic halide may be alkyl alkenyl or aryl Iodides react most and fluorides least readily bro mides are used most often Suitable solvents include hexane diethyl ether and tetrahy drofuran... 

The reaction of strong bases with aryl halides results in the generation of an aryne through loss of HX, Arynes can also be formed by reaction of aryl halides with lithium and organolithium compounds. 

B.iv.c. trans-a,pSubstituted Alkenylmetals. The accessibility of trani-a,/3-substituted alkenyhnetals is still rather limited, and only a few examples of this type of crosscoupling reactions have been reported (Table 6). Notably, trtmi-a,/3-substituted alkenylboronates can be prepared by hydroboration of 1-bromo-l-alkynes followed by subsequent treatments with organolithiums and bases, a procedure similar to that for the preparation of (Z)-/3-substituted alkenylboron compounds.t " Et The Pd-catalyzed crosscoupling reaction of the resultant organoboranes with aryl halides proceeds with complete retention of alkenyl stereochemistry to give trisubstituted alkenesP (Scheme 33). 

Next to the formation of Grignard reagents, the most important application of this reaction is the conversion of alkyl and aryl halides to organolithium compounds, but it has also been carried out with many other metals, (e.g., Na, Be, Zn, Hg, As, Sb, and Sn). With sodium, the Wurtz reaction (10-93) is an important side reaction. In some cases, where the reaction between a halide and a metal is too slow, an alloy of the metal with potassium or sodium can be used instead. The most important example is the preparation of tetraethyl lead from ethyl bromide and a Pb—Na alloy. 

Arylcopper intermediates can be generated from organolithium compounds, as in the preparation of cuprates.95 These compounds react with a second aryl halide to provide unsymmetrical biaryls in a reaction that is essentially a variant of the cuprate alkylation process discussed on p. 680. An alternative procedure involves generation of a mixed diarylcyanocuprate by sequential addition of two different aryllithium reagents to CuCN, which then undergo decomposition to biaryls on exposure to oxygen.96 The second addition must be carried out at very low temperature to prevent equilibration with the symmetrical diarylcyanocuprates. 

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 ... 

The stability of the alkyl and aryl derivatives increases with the number of phosphines bound to nickel(II). The bis-phosphine derivatives can be prepared according to equations (144)-(146) and using organomagnesium halides or organolithium compounds.1224-1231 A tetrakis phosphine complex was obtained similarly (equation 147). 

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