Carbanions coupling with

Work in the mid-1970s demonstrated that the vitamin K-dependent step in prothrombin synthesis was the conversion of glutamyl residues to y-carboxyglutamyl residues. Subsequent studies more cleady defined the role of vitamin K in this conversion and have led to the current theory that the vitamin K-dependent carboxylation reaction is essentially a two-step process which first involves generation of a carbanion at the y-position of the glutamyl (Gla) residue. This event is coupled with the epoxidation of the reduced form of vitamin K and in a subsequent step, the carbanion is carboxylated (77—80). Studies have provided thermochemical confirmation for the mechanism of vitamin K and have shown the oxidation of vitamin KH2 (15) can produce a base of sufficient strength to deprotonate the y-position of the glutamate (81—83). 

In another method for the coupling of two different allylic groups, a carbanion derived from a P,y-unsaturated thioether couples with an allylic halide. The... 

Stimulated by extensive research activities on donor/acceptor substituted stilbenes, Mullen and Klarner have reported a donor/acceptor substituted poly(4,4 -biphenyl-diylvinylene) derivative (85) in which the NR2 donor and CN acceptor substituents are located on the vinylene unit [111]. The synthesis is based on a C-C-coupling reaction of in situ generated carbanion functions with a (pseudo)cation function, followed by a subsequent elimination of MeSH with formation of the olefinic double bond. 

The above reactions proceed via free radical coupling. An alternative system for photochemically driven hydrocarbon functionalization evidently proceeds via the carbanion, which is obtained from reduction of the initially formed free radical3. The carbanion reacts with acetonitrile to give, after in situ hydrolysis, the methyl ketone, e.g., formation of (tricyclo[3.3.1.13-7]dec-1-yl)ethanone6. 

Thus, the reaction of living anionic polystyrene with AIBN, leading to chain coupling with elimination of CN , seems to be similar to that proposed by YOSHIMURA (15) for the reaction of carbanions with substituted a aminonitriles. 

The technique of the sulfur coupling reaction can be used also to prepare multiblock polymers. The technique of deactivation of carbanionic polymer with oxygen or sulfur is able to yield numerous interesting organic compounds such as novel macromolecular initiators, new macromolecular additives, and telechelic polymers. Finally, the coupling reactions can be used to build block polymers. 

The Pd(0)-catalyzed allylic alkylation developed by Tsuji and Trost is useful for creating organic frameworks that have a variety of polar functional groups (197). The reaction is formally viewed as a combination of an allylic cation and a carbanion. A number of allylic compounds that have an electronegative leaving group can be coupled with stabilized cafbanions of pKa less than 16 under mild reaction conditions (Scheme 84). Nucleophilic attack of Pd(0) species on an allylic substrate... 

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

The combination of ortho metallation and meta nucleophilic acylation was used to prepare a key intermediate in a synthesis of deoxyfrenolicin (42), as outlined in Scheme 11. The complex of anisole is orf/io-metallated with n-butyllithium and quenched with chlorotrimethylsilane the resulting [(o-(tri-methylsilyl)anisole)Cr(CO)3] (43) is then metallated again, converted to the arylcuprate, and coupled with ( )-2-hexenyl bromide to give the complex of l-trimethylsilyl-2-methoxy-3-(2-hexenyl)benzene (44). Addition of the carbanion from the cyanohydrin acetal of 4-pentenal, followed by the standard iodine oxidation and subsequent hydrolysis of the cyanohydrin acetal to regenerate the carbonyl group... 

Carbanions, such as the enolate ions of acetone, acetylmorpholine and others were un-reactive toward 1-AdI in liquid ammonia under photostimulation, and only the reduction product AdH and the dimer (1-Ad)2 were formed. It has been proposed that even though the 1-Ad radicals are formed under photostimulation, they do not couple with carbanions to give the S l product, at least at a competitive rate with other reactions121. 

The coupling takes place as if a carbanion (R ) were present and the carbanion attacked the alkyl halide to displace the halide ion. This is probably not the actual mechanism, however, because dialkylcuprates also couple with vinyl halides and aryl halides, which are incapable of undergoing SN2 substitutions. 

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