Metal-halogen exchange, with

Gilman s colour test 2, which depends on rapid metal-halogen exchange with 4-bromo-./V,7V-dimethylaniline, is positive for alkyllithium compounds [3], but not for organomagnesium compounds. 

Aryllithium reagents are formed by metal-halogen exchange with aryl hahdes or H-metal exchange with various aromatic compounds, and they react with alkyl hahdes. The reaction of 138 with u-butyllithium, for example, generated the... 

An alternative to the Simmons-Smith and Furukawa reagents is iodomethylzinc phenoxide, readily accessible by deprotonation of phenol with Et2Zn and subsequent metal-halogen exchange with CH2l2- An economically attractive method for cyclopropanation of alkenes is to use CH2Br2, which is considerably less expensive and easier to purify and store than CH2l2- ... 

Bromobenzocyclopropene (8) underwent metal-halogen exchange with toV-butyllithium selectively at C2. The lithiated product reacted with dimethylformamide to give the aldehyde 9, which was converted to 2-ethynylbenzocyclopropene (10) and 2-vinylbenzocyclopropene (11). 

The combination of metal-halogen exchange with the presence of a directing substituent can lead to regioselective metallation. ... 

We have found that copolymers of o- or p-chlorostyrene with butadiene can undergo metal-halogen exchange with n-BuLi in the presence... 

Metal/halogen exchange with 2,5-dibromopyridine leads exclusively and efficiently to 2-bromo-5-lithiopyridine in a thermodynamically controlled process it has been suggested that the 2-pyridyl anion is destabilised by electrostatic repulsion between nitrogen lone pair and the adjacent anion " this same factor is probably important in the greater difficulty found in generating 2,3-pyridyne (see section 5.3.2). The example below illustrates the use of the Weinreb amide of formic acid as a formyl-transfer reagent. ... 

In Scheme 12 the synthesis of an expanded optically active phosphine is shown. The preparation of the P substituents starts from l-bromo-3,5-dimethylbenzene which is converted into the bis(bromomethyl)bromoxylene by MBS, depicted in the upper left comer of Scheme 12. Reaction with the Na derivative of menthol forms the ether bonds to the menthyl groups starting from the benzylic positions. In the reaction with BuLi, a metal halogen exchange with the bromine substituent of the aromatic ring is the next step. Addition of CI2P-CH2-CH2-PCI2 completes the synthesis. The new... 

By Metal-Halogen Exchange with Aryl Halides... 

We foimd that aryl bromide (TFVE-Br) underwent smooth and quantitative metal-halogen exchange with /-butyllithium in ether at -78°C. The aryllithium reagent reacted readily in ether solution at low temperature with a variety of inorganic and organic electrophiles. In combination with established Grignard chemistry, new TFVE derivatives 1-3 were obtained from readily available and inexpensive substrates (Figure 6). 

---