Iodine-magnesium exchange reaction

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. ... 

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... 

Iodine-magnesium exchange reaction of allenyl iodides occurs by the action of PrMgBr in Et2O. Subsequent reaction with aldehydes or ketones provides homopropargyl alcohols with high regioselectivity (Scheme 3.96). 

Reaction of a metallated carbon nucleophile R —M with an organohalogen compound R-X leads to an ate complex 12 [71, 72], the relevance of which in lithium-halogen exchange reactions was postulated as early as 1958 by Wittig [71]. Experimental evidence for this intermediate was subsequently obtained by Reich [73, 74], and in 1986 Famham reported the first isolation of such an (iodine-based) 10-1-2 [75] ate complex [76]. In 1998, Hoffmann reported a related ate complex as an observable intermediate in an iodine-magnesium exchange reaction [77]. In the further course of the reaction, these intermediates are converted to the end products R -X and R-M [78]. 

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. 

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). 

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... 

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