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Alkyl halides vinyl carbanions

Dialkyl cuprates may also be added to aryl vinyl sulphoxides and the resulting a-sulphinyl carbanions can be treated with various electrophiles such as aldehydes, ketones and alkyl halides (equation 350)643. [Pg.355]

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. [Pg.451]

Among common carbon-carbon bond formation reactions involving carbanionic species, the nucleophilic substitution of alkyl halides with active methylene compounds in the presence of a base, e. g., malonic and acetoacetic ester syntheses, is one of the most well documented important methods in organic synthesis. Ketone enolates and protected ones such as vinyl silyl ethers are also versatile nucleophiles for the reaction with various electrophiles including alkyl halides. On the other hand, for the reaction of aryl halides with such nucleophiles to proceed, photostimulation or addition of transition metal catalysts or promoters is usually required, unless the halides are activated by strong electron-withdrawing substituents [7]. Of the metal species, palladium has proved to be especially useful, while copper may also be used in some reactions [81. Thus, aryl halides can react with a variety of substrates having acidic C-H bonds under palladium catalysis. [Pg.213]

If the monomers contain reactive groups that could be attacked by carbanions they will not be suitable for anionic polymerizations. Halogen-containing vinyl monomers are difficult to polymerize in these systems because of the elimination of alkyl halides. Interactions between many initiators and the carbonyl groups of methacrylates or acrylates necessitate the use of special reaction conditions, like very low temperatures, for the anionic polymerization of these monomers. [Pg.303]

In l-hthio vinyl sulfides (sec. 8.6) the sulfur atom stabilized the carbanion, allowing either alkylation or condensation reactions. The sulfonyl moiety can also stabilize a vinyllithium derivative. Vinyl sulfone (321), for example, was converted to the 1-lithio derivative with methyllithium.332 xhis organometallic reacted in the usual manner with alkyl halides (methyl iodide) to give the coupling product, 322. [Pg.631]

Cyclization of 47 discussed in Section 9.2.E showed an intramolecular alkylation reaction of enolates to give 49, but the formation of 50 illustrated an important competing reaction in the alkylation of enolates. An enolate anion is a bidentate nucleophile because it contains two nucleophilic centers, the carbanionic center and the oxygen, as illustrated by 90. Reaction of the O nucleophile in 90 with an alkyl halide leads to the vinyl ether 91. Reaction at the C nucleophile of 90 generates the usual alkylation product 92. Since a carb-anion is usually more nucleophilic than an alkoxy anion for common electrophiles, 92 tends to be the major product. There are several factors that can influence the relative proportion of these products, however. When... [Pg.735]

The synthetic applications of o-halobenzyl sulfones as precursors of 1,3- and 1,5-zwitter ionic synthons, have been investigated and their sulfonyl carbanions, generated by means of the phosphazene base Et-P2 reacted with different electrophiles, such as alkyl halides and aldehydes. When the alkylation was performed with ethyl bromoacetate, orf/io-substituted cinnamates were obtained after a subsequent p-elimination of sulfmic acid. When the aldol reaction was performed with paraform aldehyde, vinyl sulfones were obtained. The... [Pg.157]

In addition to diazonium salts, there are many other species that are able, once electrochemicaUy activated, to modify the surface with aromatics, unsaturated and saturated groups. These surface modifications can be achieved by (i) oxidation (amines, hydrazines, alcohols, carboxylates, carbamates, carbanions, Grignard reagents) (ii) reduction, some being closely related to diazonium salts (iodoniums, sulfonium) and other different species (vinylics, alkyl halide) (iii) spontaneously, chemically or pho-tochemically (alcenes, azides, peroxides). Note that electrochemical oxidation methods can be applied only to the materials that can withstand quite positive potentials such as carbon or Pt. This section will describe these modifications [357]. [Pg.184]

Use of the methylsulphinyl carbanion as base is recommended for the synthesis of ethers from alcohols and alkyl halides. The catalysed formation of dimethyl ether from hydrogen and carbon dioxide has been reported. Carey has described the use of the silicon-modified organolithium reagent (73) in the preparation of vinyl thioethers (Scheme 151). In order to extend the scope of this reaction to include vinyl ethers themselves, an attempt was made to metalate trimethylsilylmethyl ether use of n-buty 1-lithium resulted in nucleophilic attack on silicon, whereas t-butyl-lithium abstracted the wrong proton, as shown in Scheme 151. [Pg.202]

The same type of reaction is known starting from organic halides, the M-C bond of the catalytically active species that further undergoes CO insertion being now generated by oxidative addition of the RX substrate. The Pd° complexes catalyze the carbonylation of vinyl, aryl, benzyl and allyl halides (but not alkyl halides that have one or several (3 hydrogen atoms) in the presence of a nucleophile NuH and a base (NEts) or NuM. Various nucleophiles can be used alcohols, amines, H2 (NuH) and carbanions (NuM) ... [Pg.436]

A third method for preparation of carbanions is metal halogen exchange. An aryl or vinyl halide may be treated with an alkyllithium that gives the aryl or vinyllithium and the alkyl halide (Eq. 7.4) [12]. Vinyl bromide can be converted to vinyllithium by treatment with fert-butyllithium in ether at -78°C [13]. [Pg.209]

Vinyl halides undergo elimination by an ElcB mechanism more readily than alkyl halides because the carbanion intermediate formed from a vinyl halide has an sp hybridized C, while the carbanion derived from CH3CH2CI is sp hybridized. The higher percent -character of the sp hybridized anion makes it more stable, and therefore, it is formed more readily. [Pg.647]

A useful, although somewhat limited, method of preparing vinyl azides involves the addition of azide ion to vinyl halides with subsequent elimination of halide ion. This reaction is only possible when the halogen is located to a group which can effectively stabilize the intermediate carbanion. A number of alkyl and aryl substituted )3-chlorovinyl ketones (23) have been found to react in this way ". In many cases, however, the resulting /3-azidovinyl ketones (26) cannot... [Pg.561]

Simple sulfonyl carbanions which do not contain additional carbanion-stabilising groups, e.g. carbonyl groups or heteroatoms, can be readily alkylated in high yield by modern techniques with the use of alkyllithiums and lithium amide bases. A number of allylic halides have been successfully used. In allylic halides, the halogen directly attached to the double-bonded carbon is relatively inert towards nucleophilic attack (Scheme 41). In this way, sulfones (96) can be transformed via desulfonation into vinyl halides (97) or into ketones (98) by hydrolysis (Scheme 41). In contrast to ordinary alkyl sulfones, triflones (99) can be alkylated under mildly basic conditions (potassium carbonate in boiling acetonitrile) (Scheme 42). The ease of carbanion formation from triflones (99) arises from the additional electron-withdrawing (-1) effect of the trifluoromethyl moiety. [Pg.202]

Diketones. This alkylation of ketimines has been extended to the synthesis of 1,4-diketones by use of a 2,3-dihalopropene as the alkylating reagent. The reaction is carried out with the carbanion, prepared as described above and then diluted with IHF at -60°. The resultant vinylic halide is then hydrolyzed with sulfuric acid at -20 to 0°. [Pg.332]


See other pages where Alkyl halides vinyl carbanions is mentioned: [Pg.262]    [Pg.839]    [Pg.183]    [Pg.239]    [Pg.241]    [Pg.253]    [Pg.254]    [Pg.485]    [Pg.1485]    [Pg.1811]    [Pg.27]    [Pg.795]    [Pg.795]    [Pg.258]    [Pg.208]    [Pg.257]    [Pg.582]    [Pg.979]    [Pg.370]    [Pg.349]    [Pg.396]    [Pg.175]   
See also in sourсe #XX -- [ Pg.3 , Pg.242 ]

See also in sourсe #XX -- [ Pg.242 ]

See also in sourсe #XX -- [ Pg.3 , Pg.242 ]




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4- alkyl-2-vinyl

Alkylation carbanion

Carbanions alkyl

Carbanions alkylation

Carbanions alkylations

Carbanions vinyl halides

Carbanions vinylic

Vinyl carbanions

Vinyl halides

Vinyl, alkylation

Vinylic halides

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