Electrophilic coupling carbanions

Nucleophilic Addition-Electrophilic Coupling with a Carbanion Intermediate... 

Hulce, M. Nucleophilic Addition-Electrophilic Coupling with a Carbanion Intermediate, in Comp. Org. Synth, (eds. Trost, B. M.,Eleming, I.),... 

Both processes can be minimized by lowering the C,C-coupling temperature. No evidence for the third possible side reaction, e g., the addition of the nitro carbanion at the nitroso group of conjugated nitrosoalkene (process c), has been observed in C,C-coupling reactions due apparently to insufficiently high electrophilicity of the nitrogen atom. 

Another application of [Bu4N][Ph3SiF2] 826 involves the silicon-carbon bond cleavage of allyl-, benzyl-, and alkynylsilane derivatives 827-829.826 Subsequent reactions of the generated carbanions with electrophiles (Scheme 112) and alkyl halides (Scheme 113) provide high yields of carbon-carbon coupled products. 

In this chapter, C—N couplings, e.g. substitution reactions of carbanions on nitrogen atom of oximes to yield primary amines, have been reviewed. A list of oximes and 0-sulfonyloximes used for electrophilic amination is given in Table 6. These reagents aminate carbanions to A-organylimines as isolable intermediates which are hydrolyzed to primary amines (Scheme 53, path d Scheme 54). Depending on the organometaUic... 

The same transition metal systems which activate alkenes, alkadienes and alkynes to undergo nucleophilic attack by heteroatom nucleophiles also promote the reaction of carbon nucleophiles with these unsaturated compounds, and most of the chemistry in Scheme 1 in Section 3.1.2 of this volume is also applicable in these systems. However two additional problems which seriously limit the synthetic utility of these reactions are encountered with carbon nucleophiles. Most carbanions arc strong reducing agents, while many electrophilic metals such as palladium(II) are readily reduced. Thus, oxidative coupling of the carbanion, with concomitant reduction of the metal, is often encountered when carbon nucleophiles arc studied. In addition, catalytic cycles invariably require reoxidation of the metal used to activate the alkene [usually palladium(II)]. Since carbanions are more readily oxidized than are the metals used, catalysis of alkene, diene and alkyne alkylation has rarely been achieved. Thus, virtually all of the reactions discussed below require stoichiometric quantities of the transition metal, and are practical only when the ease of the transformation or the value of the product overcomes the inherent cost of using large amounts of often expensive transition metals. 

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