Halogen-metal exchange, and

Annulation of aryl halides with ortho side chains bearing a pendant electi ophilic moiety via treatment with an organolithium reagent, involving halogen-metal exchange and subsequent nucleophilic cyclization to form 4- to 7-membered rings. 

The preparation of aryllithium reagents can also be performed by using t-butyllithium in a halogen-metal exchange, and aqueous potassium ferricyanide as an oxidant. 

By means of halogen-metal exchange and electrophilic capture, bromosemibull-valene 372 has been functionalized in a variety of ways 2(4)-Chlorosemibull-valene has been similarly treated... 

Both diethyl (3-pyridyl)borane and diethyl (4-pyridyl)borane are readily accessible from 3-bromopyridine and 4-bromopyridine, respectively, via halogen-metal exchange and reaction with triethylborane [29-32], The two pyridylboranes have been coupled with a variety of aryl and heteroaryl halides, as exemplified by the coupling of diethyl (3-pyridyl)borane and 2-nitrophenylbromide to form phenylpyridine 39 [30, 31]. 

Carbenes, R2C (Section 14-7B) are produced by a eliminations from polyhalogen compounds with organometallic reagents. The first step is halogen-metal exchange and this is followed by elimination of metal halide ... 

Dechlorination, debromination, demethylthiolation, and demethylsulfonylation of triazole 1-oxides 448 are all formally related to halogen-metal exchange and can also be regarded as reduction processes favored by the formation of a stabilized anion. 

An enantiospecific synthesis of negstatin I (52) was accomplished efficiently with a sequence involving two C-imidazolide anion transformations. The first was coupling of a suitably protected carbohydrate intermediate with N-tritylimidazole. Direct monobromination of imidazole (51a, X = Y = H) was not feasible, except by selective halogen-metal exchange and reprotonation of dibromo intermediate (51b, X = Y = Br) [95TL6721], Introduction of the pendant acetic acid function was accomplished by C-allylation of 51c. 

Yammal, C.C., Podesta, J.C. and Rossi, R.A. (1992) Reactions of triorganostannyl ions with haloarenes in liquid ammonia. Competition between halogen-metal exchange and electron-transfer reactions. Journal of Organic Chemistry, 57, 5720-5725. 

It is essential, for successful retention of stereochemistry, to form the organolithiums by halogen-metal exchange, and not by reductive lithiation. While transmetallation of cis- and trans-24 with BuLi, quenching the organolithium 25 with ethylene oxide, gives complete retention of stereochemistry in 26. Owing to the intervention of radicals, reductive lithiation leads to considerable (but not total) epimerisation ... 

Compounds containing two halogen atoms will undergo halogen-metal exchange and cyclisation provided that the cyclisation step is faster than the second halogen-metal exchange. This is the case if both are iodine, or if one is iodine and the other bromine, or if one is a vinyl or aryl bromide or iodide. 

The faster halogen-metal exchange and controlled conformation in vinyl and aryl systems meant that aryllithiums and vinyllithiums can be cyclised remarkably efficiently onto cyclic vinylogous amides to give 179 and 180. 180 was used in a synthesis of (+)-indolizidine 209D.87... 

When Me3SiSnBu3 is treated with CsF, the fluoride anion should coordinate to the silyl group and not the stannyl group to produce a hypervalent silicate, and as a result, a stannyl anion would be generated.282 The stannyl anion reacts with vinyl iodide to produce a vinyl anion via a halogen-metal exchange and it reacts with the carbonyl group intramolecularly (Equation (113)). Aryl halides or allyl halides are also used in similar cyclizations.283,284... 

Reaction of Silyllithium with Chlorosilane Halogen-metal exchange and Si-Si Bond Cleavage Reaction... 

Treatment of l,l-dibromo-2-ethoxycyclopropane (31) with butyllithium at low temperature resulted in a halogen-metal exchange and conversion of the cyclopropane ring into a potent... 

Careful choice of reaction conditions allows 2-lithiation even in the presence of groups susceptible to attack by the reagent. At — 100°C in THE 4,5-dicyano-l-methylimidazole forms the 2-lithio compound at — 80°C butyllithium attacks one of the nitrile functions <92JHCI09I>. Even 4- and 5-chloroimidazoles can be 2-lithiated, as can 4-bromoimidazole, but when the 2-position is blocked halogen-metal exchange and direct lithiation can occur elsewhere <94JMC332>. 

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