Halide-lithium exchange reactions

SELECTIVE HALOGEN-LITHIUM EXCHANGE REACTIONS OF 2- 2 -HAL0PHENYL)ETHYL HALIDES ... 

Chlorohydrins epoxides. Chloromethyllithium is thermally unstable, but can be obtained by reaction of lithium wire with bromochloromethane. The halide-lithium exchange is markedly accelerated by sonication [(( ], which also promotes a subsequent reaction of the chloromethyllithium with an aldehyde or a ketone to form epoxides via chlorohydrins.1 Overall yields are 70-90%. 

Because the free energy of the aryl halide/lithium exchange equilibrium is essentially equal to the enthalpy change of the reaction, we consider other reactions from the same source of the general type (equation 11),... 

Alkyl organo tellurium compounds, prepared from alkane- or arenetellurolates and alkyl halides, react with butyl lithium,. 9ec-butyl lithium, /ert.-butyl lithium, or phenyl lithium. The alkyl group bonded to the tellurium atom is cleaved from the tellurium and is present in solution as the alkyl lithium that can be used for further reactions. This tellurium-lithium exchange reaction is synthetically useful, whenever the alkyl halides cannot be converted to alkyl lithiums by other, more conventional halogen exchange reactions. The following exchange reactions were successfully carried out ... 

The procedure to replace mercury in organic compounds by lithium was developed already in 1917 by Schlenk and Holtz and it is still the method of choice for the preparation of halide-free organolithium compounds. Wittig and Bickelhaupt were the first who used a mercury-lithium exchange reaction for the synthesis of a dilithiocompound not available by halogen-lithium exchange, o-dilithiobenzene 75. 

It can also be obtained by halide-lithium exchange by reaction of (Z)-BrCH=CHOC2Hs with n-butyllithium. 

The halogen-lithium exchange reaction of an aryl halide using a flow microreactor system has been discussed in the previous chapters. If the aryllithium species can be used in a coupling reaction catalyzed by a Pd complex in the flow microreactor system, this would provide an efficient and effective method of synthesis. However, the two reactions cannot simply be carried out sequentially. For... 

Coupling of certain lithiated reagents with aryl and vinyl halides is also possible.82 These reactions probably proceeds by a fast halogen-lithium exchange, generating the alkyl halide, which then undergoes substitution. This reaction has been applied to P-lithiobenzamides.83... 

Pentafluorophenyllithium can be readily prepared by direct reaction of penta-fluorophenyl halides with lithium amalgam [193,194] or lithium-hydrogen and lithium-halogen exchange reactions of pentafluorophenyl halides with alkyl-lithiums [195-205] (Scheme 70). 

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