Rieke’s activated magnesium

Mg(CHPhCH=CHCHPh) from Rieke s active magnesium (Reduction of MgXj with Li/naphthalene) [3 ... 

Highly reactive form (5, 419). Details for the preparation of Rieke s activated and pyrophoric magnesium have been submitted to Organic Synthesis. The powder should be kept under argon. The preparation includes synthesis of benzoic acid in 70-897o yield from bromobenzene. 

Highly activated magnesium, prepared using Rieke s method (see 10.2.3.2.1 and 10.2.3.2.3), reacts with 1,3-dienes, including 1,3-butadiene, isoprene, myrcene and ( ),( )-1,4-diphenyl-1,3-butadiene . 

Little is known of alkyl and arylcadmium halides. They cannot be obtained by reacting cadmium metal with organic halides, unless active cadmium is prepared by Rieke s method (p. 18). The dialkyls are usually prepared by the Grignard method. Their main use is to convert acyl halides into ketones. Pure Et Cd does not react with benzoyl chloride, but it does so in the presence of the magnesium salts which are by-products in the Grignard synthesis. 

Walborsky and Rachon have also reported on the use of Rieke magnesium to obtain reaction with (S)-(+)-l-bromo-l-methyl-2,2-diphenylcyclopropane at —65°C to afford a chiral Grignard reagent that is 33-43% optically pure [73]. In 1961, Young and Walborsky [74] demonstrated that the reaction of chiral (S)-(+ )-l-bromo-l-methyl-2,2-diphenyl-cyclopropane (Table 5 1) with magnesium powder resulted in the formation of a chiral Grignard reagent as evidenced by the fact that on carbonation of the reaction mixture an optically active acid was obtained with an optical purity of approximately 12-18%. 

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