Organomagnesium preparation

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 term Grignard reaction refers to both the preparation of a class of organomagnesium haUde compounds and their subsequent reaction with a wide variety of organic and inorganic substrates. As such it has had a wide and profound influence on synthetic chemistry since its first elucidation by Victor Grignard at the beginning of the twentieth century. 

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). 

Organolithium and organomagnesium compounds find their- chief use in the preparation of alcohols by reaction with aldehydes and ketones. Before discussing these reactions, let us first exanine the reactions of these organometallic compounds with proton donors. 

Oddo reported that the organomagnesium derivatives of p3Trole, indole, skatole, and carbazole could be prepared in a single operation by mixing the parent heterocyclic compound with an alkyl halide and magnesium in anhydrous ether.The product formed was reported to be the same as that obtained by the more conventional procedure. However, this approach to the synthesis of the indole Grignard reagents does not seem to have been exploited in subsequent work. 

An interesting example of the organomagnesium synthesis is to be found in the use of 1,4-addition of the Grignard reagent to 4-alkyl-ideneisoxazol-5-ones (91) to prepare saturated isoxazol-5-ones (92). 

Allenyl and 1- and 2-alkynyl sulfoxides have also been prepared by reaction of organomagnesium halides with sulfinate ester 19. 1-Alkynyl p-tolyl sulfoxides were prepared in good yield from 1-alkynylmagnesium halides plus ester 19 in toluene (equation ll)63. The corresponding organolithium compound was unsatisfactory as a... 

Arylboronic acids have traditionally been prepared via the addition of an organomagnesium or organolithium intermediate to a trialkyl borate. Subsequent acidic hydrolysis produces the free arylboronic acid. This limits the type of arylboronic acids one can access via this method, as many functional groups are not compatible with the conditions necessary to generate the required organometallic species, or these species may not be stable intermediates. 

As with organomagnesium reagents, there is usually loss of stereochemical integrity at the site of reaction during the preparation of alkyllithium compounds.25 Alkenyllithium reagents can usually be prepared with retention of configuration of the double bond.26,27... 

The preparation of ketones proceeds conveniently by reaction of imidazolides with organomagnesium reagents, as shown in Table 14-6 for several examples of purely aromatic, aromatic-aliphatic, and purely aliphatic ketones. The yields are very satisfactory even for purely aliphatic ketones, since in this case, too, alcohol formation is completely suppressed.t851,t861... 

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