Metal-lithium exchange reactions

Metal-lithium exchange reaction of a silyl metal compound (especially Group 12 metals) with alkyllithium or lithium metal. 

Metal-lithium exchange reactions provide alternative sources of vinyl-lithiums. 

As pointed out earlier (Sect. 7.1), alkyl lithium reagents induce metal-hydrogen exchange reactions. This possibility was investigated first by Paddock and coworkers [266,227]. They have found that the anion generated by the reaction of methylphosphazene with n-butyl lithium interacts with electrophiles such... 

Both 1 and 2 are stereochemically stable and shelf stable -metalated ethers. Subsequent tin-lithium exchange reaction with bulyllithium occurs as expected with retention of configuration in both cases51. 

The classical tin-lithium exchange reaction was first applied to cyclopropanes in the stereospecific transformation of 7-ewrfo-bromo-7-ex o-trimethyltinnorcarane to the corresponding 7-exo-lithio compound with BuLi in THF, at -95 °C (vide supra)10. The retention of configuration in cyclopropyl tin-lithium exchange reactions has also been confirmed in monocyclic 2-metallacyclopropane carboxamides60. More recently, this metal exchange reaction was used for the preparation of sensitive methylenecyclopropanes (equation 21)61. 

Lithiotrisilanes, which are used as precursors to polysilane dendrimers, have been obtained by a mercury-lithium exchange reaction (equation 25)56,61. The terminally metalated trisilane Me3Si(Me2Si)2Li has been synthesized analogously56. 

Allylation of carbonyl and imino groups is one of the most convenient methods for the introduction of allylic functions.107-110 Allylic tin compounds have high interaction between C=C and C-Sn bonds which makes them more reactive than the corresponding silicon derivatives.111,112 In spite of their high reactivity, tin compounds are stable enough to be isolated and to react at ambient temperature under aerobic conditions. These factors allow them to be applicable to various types of reactions, for example, thermal,113 high-pressure,116 transition metal-catalyzed,117,118 radical,119,120 photochemical,121,122 tin-lithium exchange reactions,108,113 and so on. A broad... 

For the synthesis of a-selenoalkyllithiums, the selenium-lithium exchange reaction is a good alternative to the almost impossible metallation of unactivated selenides.Thus it has been found that a large variety of selenoacetals, often readily available from carbonyl compounds and selenols, react with butyllithiums to provide a-selenoalkyllithiums - in very high yields (Scheme 2 see also Section 2.6.2.3). 

L. S. Fuller, B. Iddon and K. A. Smith, Thienothiophenes. 2. Synthesis, metallation and bromine—>lithium exchange reactions of thieno[3,2-i>]thiophene and its polybromo derivatives, /. Chem. Soc., Perkin Trans. 1, 3465-3470 (1997). 

A quite different version of the Li-Barbier reaction, which was recently published [38], has already been referred to on p. 86 n-Butyllithium was used to generate the intermediate lithium compound from iV-(2-iodobenzyl) phenacyla-mine, achieving the first ever reported intramolecular Barbier reaction, with an aryl halide. As was the case with the iodonitrile (p. 86 of this Section), the metal-halogen exchange reaction of the n-butyllithium proved to be much faster than the carbonyl addition reaction. 

Fig. 22 Seiected examples of the use of lithium alkyl magnesiates in metal-halogen exchange reactions with aryl halides...

Regiospecific Lithiation Carbonyl Equivalents Alkenyl-lithiums Metal-Lithium Exchange Miscellaneous Reactions... 

Reactivity and yields are greatly enhanced by the presence of 0.5-1% Na in the Li. The reaction is also generally available for the preparation of metal alkyls of the heavier Group 1 metals. Lithium aryls are best prepared by metal-halogen exchange using LiBu" and an aryl iodide, and transmetalation is the most convenient route to vinyl, allyl and other unsaturated derivatives ... 

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