Grignard reagents carbomagnesiation

When the phenyl-substituted alkynyl sulfone 42 is used as a substrate for the Cu-catalyzed carbomagnesiation, interesting nucleophile-dependent stereoselectivity is observed. While the use of allyl Grignard reagent results in a syn addition, the use of aryl Grignard reagent results in an awh -carbomagnesiation (Scheme 25). ... 

Hydroxymethylated cyclopropenes, which can be readily prepared by Rh-catalyzed reaction of diazoesters and alkynes, are good snbstrates for nncatalyzed and Cu-catalyzed carbomagnesiation. For example, a range of substitnted cyclopropanes 82 can be synthesized in a regio- and stereoselective fashion by the Cu-catalyzed addition of Grignard reagents to (3-hydroxymethyl)cyclopropenes 81 (Scheme 57) . 

The carbomagnesiation of vinyisiianes is a powerful method for the generation of synthetically useful a-silyl carbanions. However, simple vinyisiianes such as trimethyl(vinyl) silane do not undergo carbometalation with Grignard reagents (Scheme 59) °. In early days, only limited success had been achieved by using perfluorovinylsilanes °°. 

One of the classical solutions to overcome the low reactivity is to render the carbomagnesiation intramolecular. For example, Utimoto and coworkers reported that the reaction of ( )-6-bromo-3-methyl-l-trimethylsilyl-l-hexene (85) with magnesium produces the corresponding Grignard reagent 86, which intramolecularly adds to the vinylsilane moiety from the less hindered side affording a single stereoisomer of cycUzed product 87 (Scheme 60) °°. 

The carbomagnesiation of alkenes has been extensively investigated in the last 40 years and several reactions with high synthetic potential have been discovered. The addition of Grignard reagents to non-functionalized alkenes usually requires severe reaction conditions and only the zirconium-catalyzed... 

Terminal alkynes are readily deprotonated by Grignard reagents, and no further addition occurs to al-kynylmagnesium halides. In the presence of transition metal complexes of titanium,70 iron,70 rhodium,71 nickel,70 72 palladium70 or copper,73 the carbomagnesiation takes place in moderate yields. The regio- and stereo-selectivity of the additions are variable. In the presence of a copper(I) salt, however, only the syn... 

Allylic and allenyl Grignard reagents are available by conjugate carbomagnesiation of... 

Addition to ketones. Participation of the cyclic ether moiety in Cp2ZrCl2-catalyzed carbomagnesiation of terminal alkenes, e.g., (1), has been observed. Grignard reagents resulting from the transformation contain rather special structures. 

Scheme 10.20 Copper-catalyzed regioselective carbomagnesiation of non-activated 1,3-dienes with branched alkyl Grignard reagents [22].

Scheme 10.25 Nickel-catalyzed carbomagnesiation of methylenecyclopropanes with aryl Grignard s reagents proximal carbon-carbon bond cleavage [26].

Scheme 10.27 Deuterium-labeling experiment in the nickel-catalyzed carbomagnesiation of MCP derivatives with vinyl Grignard s reagents [26].

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