Organomagnesium compound

Organomagnesium halides (the Grignard reagents) are still the organometallic compounds most widely used in preparative organic chemistry, owing this to the relative ease of their preparation and handling. 

The method applied almost exclusively to their preparation is direct reaction of an alkyl or aryl halide with metallic magnesium, in accordance with the equation  

It is extremely widely applicable, for Grignard reagents can be prepared from almost every type of alkyl and aryl halide except the fluorides. 

Ioffe and A. N. Nesmeyanov, The Organic Compounds of Magnesium, Beryllium, Calcium, Strontium, and Barium, North-Holland, Amsterdam, 1967. 

The amount of magnesium used is normally that equivalent to the halide, but sometimes an excess must be taken. 

See also page 420. Section 2.6 page 506, Section 3.22 and page 514, Section 3.24. 

PhSCH—CHCH=CHBr —---------------------- R1CH=CHCH=CHR2 

CuIorPd(PPii3)4 V alkyl, 1 benzylic, aiyl BCSJ 2831 (1981) 

Coupling of arylmagnesium halides takes place with aryl, alkenyl, and alkyl halides. Reaction of electron-rich chlorides can be carried out using carbene ligand XVI-2. For example, the coupling product of 4-chloroanisole (2) with phenylmag-nesium bromide (1) was obtained in high yield at room temperature [65]. Also 

Highly asymmetric coupling of Grignard reagents is possible. The axially chiral (5)-biaryl 9 was prepared with 93 % ee in 87 % yield by the reaction of the bistriflate 7 with PhMgBr. (5)-phephos (VII-7) was the best chiral ligand [70]. The 

Some heteroaryl halides are electron-deficient and reactive. 3-Pyridylmagnesium chloride (13) was prepared efficiently by the treatment of 3-bromopyridine (12) with isopropylmagnesium chloride, and 2-(3-pyridyl)pyridine (15) was prepared by coupling 13 with 2-bromopyridine (14) using DPPF as a ligand [71]. 

The pure cw-stilbene derivative 18 was prepared cleanly in high yield by the reaction of sterically hindered 2,6-dimethylphenylmagnesium bromide (16) with tra 5 -3,4-dibromo-3-hexene (17), which is easier to prepare than the corresponding cw-dibromide [72]. 

Interestingly, alkyl chlorides can be used for the coupling without undergoing y3-H elimination. The best ligand for the efficient coupling of 1-chlorohexane is PCy3, and the reaction in NMP or DMAC as a solvent gives n-hexylbenzene (19), 

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Organohthium and organomagnesium compounds find their chief use m the prepa ration of alcohols by reaction with aldehydes and ketones Before discussing these reac tions let us first examine the reactions of these organometallic compounds with proton donors... 

Organohthium and organomagnesium compounds are stable species when prepared m suitable solvents such as diethyl ether They are strongly basic however and react instantly with proton donors even as weakly acidic as water and alcohols A proton is transferred from the hydroxyl group to the negatively polarized carbon of the organometallic compound to form a hydrocarbon... 

The carbon-metal bonds of organolithium and organomagnesium compounds have appreciable carbamomc character Carbanions rank among the strongest bases that we 11 see m this text Their conjugate acids are hydrocarbons—very weak acids indeed The equilibrium constants for ionization of hydrocarbons are much smaller than the s for water and alcohols thus hydrocarbons have much larger pA s... 

Victor Grignard was led to study organomagnesium compounds because of ear her work he performed with organic derivatives of zinc... 

Magnesium methylate is used as a drying agent for alcohols and other organic solvents and as an intermediate in various manufacturing processes, eg, for organomagnesium compounds (79), orthocarbonic esters (80), and for oxide coatings. 

In earlier studies [f J], it was shown that pentafluorobenzene has an acidic aryl hydrogen capable of metalation by organolithium or organomagnesium compounds to yield perfluorophenylorganometallic compounds... 

Anhydrous diethyl ether is the customary solvent used when preparing organomagnesium compounds. Sometimes the reaction does not begin readily, but once started, it is exothermic and maintains the temperature of the reaction mixture at the boiling point of diethyl ether (35°C). 

Grignard reagent (Section 14.4) An organomagnesium compound of the type RMgX formed by the reaction of magnesium with an alkyl or aryl halide. 

Reactions of Enamine Salts with OrganometalUc Compounds Organolithium and organomagnesium compounds react with enamine salts to give amines substituted on the ix-carbon atoms. The treatment of. -dehydroquinolizidinium perchlorate (163) with alkylmagnesium halides gives 9-alkylated quinolizidines (164) (252,256). Formation of... 

Heterocyclization with participation of organomagnesium compounds 99JOM(575)l. 

A related cleavage reaction (165 166) occurs on the treatment of isoxazoles with organomagnesium compounds.This reaction considerably hinders the use of the Grignard reaction in the isoxazole series (see Section IV,D) in it the activity of the organo-... 

The cleavage of the isoxazole ring by organomagnesium compounds may proceed by either one or both of two alternative mechanisms. Magnesium subhalides produced during the associated reaction may act as reducing agents as proved in specific cases.Another possibility is that the reduction involves a six-membered cyclic complex (171). 

Under the conditions used for the reductive cleavage of the O—N bond in isoxazoles, a similar reaction readily occurs with isoxa-zolines, e.g. on treatment with organomagnesium compounds and on catalytic hydrogenation.- Hydrogenolysis of the O—N bond (180 181 182 183) was used to elucidate the structure of isoxa-zolones from -ketoesters. -... 

Addition of organomagnesium compounds to polarized multiple bonds O OMgX OH... 

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