Magnesium, reaction of with alkyl and aryl

McGwire, Mark, 1041 Macrolide antibiotics, 758 Magnesium, reaction of with alkyl and aryl halides, 550-551, 571 Magnetic field... 

Alkyl and aryl iodides usually react with magnesium more rapidly than the corresponding bromides, and the bromides very much more rapidly than the chlorides. Aryl (as distinct from alkyl) chlorides have usually only a slow reaction with magnesium and are therefore very rarely used. With alkyl and aryl iodides in particular, however, a side reaction often occurs with the formation of a hydrocarbon and magnesium iodide ... 

There are very few studies of the Barbier reaction mechanism with magnesium as the metallic source. However, with the discovery that the reaction will often proceed to a greater extent with other metals such as lithium, some good mechanistic studies have been conducted. The focus of most of these studies has been the reaction of an alkyl or aryl halide with a ketone. The conclusions drawn from these studies are considered to be valid for magnesium as well, and they will be referenced in this section. 

Reactions of Activated Magnesium with Alkyl and Aryl Halides... 

Such cyclohexadienes are easily oxidizable to benzenes (often by atmospheric oxygen), so this reaction becomes a method of alkylating and arylating suitably substituted (usually hindered) aryl ketones. A similar reaction has been reported for aromatic nitro compounds where 1,3,5-trinitrobenzene reacts with excess methyl-magnesium halide to give 2,4,6-trinitro-l,3,5-trimethylcyclohexane. Both... 

New 3-desoxyanthocyanidins have been prepared according to a Grignard reaction of some flavones with appropriate alkyl- and aryl-magnesium bromides. The reaction of 5,7-dihydroxyflavone (chrysin) with an excess of phenylmagnesium bromide in THF under reflux conditions, followed by hydrochloric acid hydrolysis, afforded 1 in Scheme 10.2. Flavylium salts bearing a substituent at the 4-position are important compounds since they are known to be less sensitive to nucleophiles, especially water, and they give only minor amounts of the colorless pseudobases. ... 

Like magnesium, lithium reacts with alkyl halides, vinyl halides, and aryl halides to form organometallic compounds. Ether is not necessary for this reaction. Organolithium reagents are made and used in a wide variety of solvents, including alkanes. 

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