Vinyl carbanions nucleophilic addition with

Because of thetr electron deficient nature, fluoroolefms are often nucleophihcally attacked by alcohols and alkoxides Ethers are commonly produced by these addition and addition-elimination reactions The wide availability of alcohols and fliioroolefins has established the generality of the nucleophilic addition reactions The mechanism of the addition reaction is generally believed to proceed by attack at a vinylic carbon to produce an intermediate fluorocarbanion as the rate-determining slow step The intermediate carbanion may react with a proton source to yield the saturated addition product Alternatively, the intermediate carbanion may, by elimination of P-halogen, lead to an unsaturated ether, often an enol or vinylic ether These addition and addition-elimination reactions have been previously reviewed [1, 2] The intermediate carbanions resulting from nucleophilic attack on fluoroolefins have also been trapped in situ with carbon dioxide, carbonates, and esters of fluorinated acids [3, 4, 5] (equations 1 and 2)... 

Treatment of a-lithionitriles with vinylic sulfones resulted in the formation of cyclized products, i.e., 3-oxothian-l, 1-dioxides 346 or cyclopropane derivatives 348. When a-lithiated aliphatic nitriles were used, carbanions 343, formed by the nucleophilic addition,... 

Dehydrobromination of bromotrifluoropropene affords the more expensive trifluoropropyne [237], which was metallated in situ and trapped with an aldehyde in the TIT group s [238]synthesis of 2,6-dideoxy-6,6,6-trifluorosugars (Eq. 77). Allylic alcohols derived from adducts of this type have been transformed into trifluoromethyl lactones via [3,3] -Claisen rearrangements and subsequent iodolactonisation [239]. Relatively weak bases such as hydroxide anion can be used to perform the dehydrobromination and when the alkyne is generated in the presence of nucleophilic species, addition usually follows. Trifluoromethyl enol ethers were prepared (stereoselectively) in this way (Eq. 78) the key intermediate is presumably a transient vinyl carbanion which protonates before defluorination can occur [240]. Palladium(II)-catalysed alkenylation or aryla-tion then proceeds [241]. 

The synthesis of 4-alkyl thioketones is possible by exploiting the stabilizing effect of a sulfur atom upon an adjacent carbanionic center. Ambident allylic anions react so that conjugate addition proceeds exclusively with the a-carbon of the nucleophile,129 243 244 as illustrated in equation (S3) 245 arylsulfinyl and arylsulfonyl groups normally246 behave similarly.247-249 Sulfur-stabilized vinylic carbanions can be prepared and function as Michael donors in difunctionalization sequences.250... 

Reactions which are apparently stereospecific occur in the nucleophilic displacement of vinylic iodide [31] in the electron-deficient alkenes E- and Z-24 shown in Scheme 9.14. With ethanolic toluenethiolate, the sole detectable product from the reaction of -24 is -25. However, -25 is also the sole detectable product from the reaction of Z-24. This stereoconvergence demands that the stereoisomers react through a common intermediate, and it was reasonably suggested that initial nucleophilic addition of the thiolate anion yields a resonance-stabilised carbanion (26) whose stereoisomerisation, again by rotation about a carbon-carbon single bond, is much faster than the loss of iodide to yield the substitution product ( fy). 

The fruitfulness of the idea of a stepwise addition with an independent variation of the addends was brilliantly illustrated by Normant s studies, which resulted in the elaboration of a general method of alkene synthesis based on the reaction of alkyne carbometallation. Basically this reaction represents a case of the well-known nucleophilic addition to a carbon-carbon triple bond. In the Normant reaction, however, the initial addition of a nucleophile (an organome-tallic reagent) across the triple bond results in the formation of a stabilized carbanion-like intermediate equivalent to a vinyl carbanion. This intermediate can similarly be further reacted with an external electrophile. Most typically, copper-modified Mg or Li reagents, which are unable to react with acidic acetylenic hydrogens, are used in this sequence. 

Conjugate nucleophilic addition of methyl, vinyl, allyl, and malonate groups to l-(2-indolyl)but-2-enecarbonitrile has been effected with a range of organometallic carbanions, for example, the lithium derivative of ethyl vinyl ether gives the product (390), which can be cyclized to a pyrrolof 1,2-ajindole (391) (Scheme 130) <9ITL7237>. 

Substituted imidazoles A/-R Im undergo a stereoselective, uncatalysed ring opening on reaction with ynones PhC=CCOR and water in MeCN at 45-60 C to produce (Z,Z)-propenylaminoethenylformamides R N(CH=0)CH=CH-NH-C(Ph)=COR. The reaction is believed to proceed via a zwitterionic vinyl carbanion, generated by the initial nucleophilic addition of imidazole to the C=C bond. ... 

Reaction of sodium methoxide with (147) does not give 2,3,4,5-tetrachloro-biphenyl as earlier reported in this study, (148) and (149) were obtained. In view of the failure of addition to styrene under similar reaction conditions it is likely that the chlorines activate the double bond to nucleophilic attack. With (150) two major products, (151) and (152), were found. The preference for attack at the double bonds is considered to be finely balanced. The suggestion of intermediate non-classical carbanions seems unlikely no tricyclic products are observed. In a detailed investigation, other polyhalogenonorbornadienes were observed to undergo similar vinylic substitution or addition. The products... 

The success of the reaction depends on the formation of the zwitterionic 7t-allylpalladium complex, which is subsequently trapped with the electron-poor olefins to afford the desired vinylcyclopentane. This is achieved through a nucleophilic addition of Pd onto the vinyl group, which results in an opening of the cyclopropane ring, revealing the zwitterionic 7i-allylpalladium complex. The presence of the ester moieties stabilizes the carbanion, while the carbocation is stabilized by the 7t-allylpalladium complex. This is followed by a Michael addition of the electron poor olefins onto the carbanion to form the second intermediate, which rapidly... 

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