Grignard reagent, carbanion chemistry

You have already had considerable experience with carbanionic compounds and their applications in synthetic organic chemistry The first was acetyhde ion m Chapter 9 followed m Chapter 14 by organometallic compounds—Grignard reagents for example—that act as sources of negatively polarized carbon In Chapter 18 you learned that enolate ions—reactive intermediates generated from aldehydes and ketones—are nucleophilic and that this property can be used to advantage as a method for carbon-carbon bond formation... 

The origin of the alkyl or aryl group (R) in Eq. (20) is as well an important issue in the development of C, chemistry involving C02. We will not be concerned with this question at present other than to mention that the carbanion in Eq. (20) is usually derived from lithium or Grignard reagents, or alkyl- or arylhalides [Eqs. (21) and (22)]. An alternate source, e.g., olefins,... 

Carbon nucleophiles play a central role in organic chemistry, as they form the basis of carbon-carbon bond formation. A few are shown in Figure 1.2, including such carbanionic species as organolithiums (RLi), Grignard reagents (typically written as RMgBr), and the cyanide (CN ) and acetylide (R-C=C ) anions. Other examples such as enolates, enols, and enamines will be briefly discussed in Section 1.15. 

Carbon-carbon bond formation is one of the oldest and most important topics of organic chemistry, and for a long time has been dominated by Friedel-Crafts and Grignard reactions. The former are based on stabilized carbocations as reagents and are exemplified by benzene alkylation (Equation 1), while the latter involve stabilized carbanions and are exemplified by acetone alkylation (Equation 2). 

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