Halogen exchange amide halides

Lithium-halogen exchange. The reagent is useful for preparation of organo-lithiums from acetal-containing substrates, dihaloarenes (monofunctionalization), and halopyridines. Dechlorination of /V-(/3-chloroalkyl)amides apparently cannot be achieved with BuLi alone (stops at (V-deprotonation ), and the use of LN is required." Of course the N,C-dithio derivatives may be employed in C-C bond formation (remarkably the coupling with aryl and vinyl halides). Barbier-type reactions have been achieved."... 

Successful lithiation of aryl halides—carbocyclic or heterocyclic—with alkyUithiums is, however, the exception rather than the rule. The instability of ortholithiated carbocyclic aryl halides towards benzyne formation is always a limiting feature of their use, and aryl bromides and iodides undergo halogen-metal exchange in preference to deprotonation. Lithium amide bases avoid the second of these problems, but work well only with aryl halides benefitting from some additional acidifying feature. Chlorobenzene and bromobenzene can be lithiated with moderate yield and selectivity by LDA or LiTMP at -75 or -100 °C . 

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