Iodine-magnesium exchange

This iodine-magnesium exchange can also be performed with heterocyclic iodides, such as the functionalized pyridine 16 [21] or the iodouracil derivative 17 (Scheme 2.5) [22]. In both cases, the intermediate organomagnesium reagent can... 

The functionalized arylzinc reagents are best prepared either starting from an aryllithium obtained by halogen-lithium exchange followed by a low-temperature (-80°C) transmetalation with ZnBrj or by performing an iodine-magnesium exchange reaction. The latter reaction tolerates temperatures up to -30°C and is more convenient for industrial applications. ... 

Functionalized aryl Grignard compounds, prepared by iodine-magnesium exchange according to the procedure reported by Cahiez, Knochel and coworkers in 1998, can be efficiently acylated. It is thus possible to prepare various polyfunctionalized diaryl ketones (Scheme 14). ... 

The chemistry of organomagnesium ate complexes TABLE 6. Iodine-magnesium exchange of aryl iodides... 

The reactions of 2-iodopyrazine, 2-methylsulfanyl-4-iodopyrimidine and 3-iodo-6-phenylpyridazine with lithium tributylmagnesate resulted in very efficient iodine-magnesium exchange to yield the corresponding heteroarylmagnesium species (equations 35-37)" °. The reactions with carbonyl compounds and diphenyl disulfide proceeded with good yields. The reactions proceeded smoothly, and neither the starting iodide nor any butylated compounds derived from nucleophilic addition to the heteroaromatic nuclei were observed. 

Lithium tributylmagnesate induced iodine-magnesium exchange reaction of 5-alkoxy-3-iodomethyl-l-oxacyclopentanes (Scheme 16). A following intramolecular nucleophilic substitution led to construction of a cyclopropane with concomitant opening of the oxa-cyclopentane ring. 

Magnesium carbenoids (5 and 6) were generated from a geminal diiodoalkane by diastereoselective iodine-magnesium exchange reaction with isopropylmagnesium halide in THF at —78°C for 45 min (Scheme 1). Subsequent reaction of the magnesium... 

Similarly, nitroarenes can also be lithiated (Scheme 5.43), but reactions of meta-lated nitroarenes with electrophiles only proceed cleanly if the metalation is performed in the presence of the electrophile [403], Otherwise, the metalated arene can reduce nitro groups to nitroso groups, which quickly react with additional organo-metallic reagent to yield hydroxylamines [404, 405], Nitroarylmagnesium halides can be prepared by iodine-magnesium exchange at -80 °C to -40 °C, and react with electrophiles in the expected way [6] (Scheme 5.43). 

The iodine-magnesium exchange on ort o-iodoaryl sulfonates leads, after warming up, to the formation of functionalized arynes, which can be trapped by dienes or nucleophiles (Scheme 17).45,46 Hetaryl iodides react with 7-PrMgCl in THF giving the corresponding magnesium compounds in excellent yields (Scheme 18).47,47a,47b... 

Substituted pyridines, quinolines, and diazines react with polyfunctionalized aryl Grignard reagents, obtained by iodine-magnesium exchange under very mild conditions in the presence of PdCl2(dppf) as a catalyst (Scheme 48). 136,137... 

Reaction of aryl Grignard compounds, obtained in situ by iodine-magnesium exchange, with C0CI2, presumably generates aryl radicals. In the presence of a double bond or aromatic ring an intramolecular radical cyclization may take place. This reaction was used for the synthesis of spiro-indolines.244 Oshima has applied cobalt-mediated tandem radical cyclization-cross-coupling reaction for the synthesis of benzyl-substituted heterocycles (Scheme 80).245... 

A convenient synthesis of aryl glycines from Grignard reagents, prepared via iodine-magnesium exchange, was performed by the reaction with N-Boc-iminomalonate (from diethyl mesoxalate and BocN=PPh3). The reaction... 

A flexible and convergent access to 2,3-disubstituted benzo[b]thiophenes has been developed (Scheme 22). The most concise approach involves a sequential coupling of an o-bromoiodobenzene with benzylthiol and zinc acetylides leading to the adduct 78. Treatment with iodine followed by an iodine/magnesium exchange and acylation provides the polyfunctional benzofuran derivatives. a... 

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