Carbonation acetylene anion

The reduction of acetylenic tellurides to the vinylic ones is achieved by treatment with NaBH4 in EtOH. The formal unusual reduction of the carbon triple bond by NaBH4 can be rationalized involving the attack of a hydride ion to the tellurium atom producing a tellurol and an acetylenic anion followed by the addition of the tellurolate anion to the acetylene, DIBAL-H has later been employed as a reducing agent. ... 

The former, an acetylenic anion, is stabilized by the increased electronegativity of sp-hybridized carbon and the latter, the allyl anion, by the jr-delo-calization of the negative charge. 

One nucleophilic addition of an acetylenic anion is used to construct the first half of the citral molecule and a second extends it to the full 10 carbon atoms. 

Some methods of adding two carbons to the alcohol involves the use of an ethyl Grignard reagent or an acetylene anion. Of these methods, the use of the acetylene anion is the most feasible it will react with an alkyl halide via an Sno mechanism. The alkyne formed can then be converted into the desired product. The synthesis which employs this method is shown below ... 

Despite their high dissociation energy of 133 kcal/mol, sp C—H bonds are prone to C—H bond activation. Indeed, the simplest alkyne, acetylene, has a rather small pR, value of25—26, which makes it a weak acid in organ-ometaUic chemistry, and can be deprotonated by a strong base such as a nitrogen- or carbon-based anion. Therefore, the reaction between a metal alkyl complex and a primary alkyne is usually thermodynamically favorable and resembles a classical acid—base metathesis reaction. 

Terminal alkyne anions are popular reagents for the acyl anion synthons (RCHjCO"). If this nucleophile is added to aldehydes or ketones, the triple bond remains. This can be con verted to an alkynemercury(II) complex with mercuric salts and is hydrated with water or acids to form ketones (M.M.T. Khan, 1974). The more substituted carbon atom of the al-kynes is converted preferentially into a carbonyl group. Highly substituted a-hydroxyketones are available by this method (J.A. Katzenellenbogen, 1973). Acetylene itself can react with two molecules of an aldehyde or a ketone (V. jager, 1977). Hydration then leads to 1,4-dihydroxy-2-butanones. The 1,4-diols tend to condense to tetrahydrofuran derivatives in the presence of acids. 

The acidity mcreases as carbon becomes more electronegative Ionization of acetylene gives an anion m which the unshared electron pair occupies an orbital with 50% s character... 

Although acetylene and terminal alkynes are far stronger acids than other hydro carbons we must remember that they are nevertheless very weak acids—much weaker than water and alcohols for example Hydroxide ion is too weak a base to convert acety lene to its anion m meaningful amounts The position of the equilibrium described by the following equation lies overwhelmingly to the left... 

Anions of acetylene and terminal alkynes are nucleophilic and react with methyl and primary alkyl halides to form carbon-carbon bonds by nucleophilic substitution Some useful applications of this reaction will be discussed m the following section... 

The halogen migration is completely suppressed by halogen-metal exchange when the chloroethynyl group is in position 5 of the pyrazole ring. The concentrations of 3-pyrazolyl and 4-pyrazolyl anions are probably small, and they cannot compete with NH2 anions for chlorine bonded to the acetylenic carbon. 

Retrosynthetic cleavage of the indicated bond in 9 provides acetylenic aldehyde 23 as a potential precursor. It was anticipated that the action of a suitable base on 23 would result in the formation of an acetylide anion, a competent carbon nucleophile that could... 

Eisch, Behrooz and Galle196 give compelling evidence for the intervention of radical species in the desulphonylation of certain acetylenic or aryl sulphones with metal alkyls having a lower oxidation potential at the anionic carbon. The primary evidence presented by these workers is that the reaction of 5-hexenylmagnesium chloride outlined in equation (85) gives a mixture of desulphonylation products, in accord with the known behaviour of the 5-hexenyl radical, in which the cyclopentylmethyl radical is also formed. 

In adding two molecules of acetone to acetylenes, there are no problems of chemoselectlvity as the dl-anion (15) of the monoadduct reacts preferentially on carbon. Diol (13) cannot bo Isolated as it cyclises under the hydration conditions. 

The mechanism of the reaction of tertiary phosphites with halogeno-acetylenes has been investigated by two groups of workers. - Initial attack of phosphite could be on carbon to give the anion (78), which can eliminate halide, or on halogen to give the ion pair (79) which leads to the same intermediate (80). In both cases an Arbusov reaction would give the isolated product (81). 

Dick turned up some interesting chemistry of caprolactam and its O-alkyl imino ethers. He and collaborators went on to explore the chemistry of allene, for example, its reactions with acetylene, carbon monoxide, and tetrafluo-roethylene. He did extensive work on the chemistry of cyclooctatetraene and of ferrocene. In the cyanocarbon area he collaborated on studies of the anion radical of tetracyanoethylene, that is, tetracyanoethylene bearing an extra electron. He was author or coauthor of 45 papers and 16 U.S. Patents that came out of the Central Research Department. 

As one can notice, the monoUthiated allenic isomer seems to be preferred in almost aU cases in hexane. However, West and Gomowicz reported that the IR spectrum of monolithio-I,3-bis(trimethylsilyl)-3-phenylpropyne exhibits two bands at 2000 and 1850 cm and attributed them to the acetylenic and allenic forms ". In light of the new interpretation, Priester and coworkers ascribed the band at 2000 cm to the propargyl anion, where both phenyl and silicon stabilized the charge at carbon atom 3 . 

C-H insertion of an alkylidene carbene intermediate, which was generated via the Michael addition of a sulfinate anion to the acetylenic p-carbon. In MeOH,... 

The first metal-olefin complex was reported in 1827 by Zeise, but, until a few years ago, only palladium(II), platinum(Il), copper(I), silver(I), and mercury(II) were known to form such complexes (67, 188) and the nature of the bonding was not satisfactorily explained until 1951. However, recent work has shown that complexes of unsaturated hydrocarbons with metals of the vanadium, chromium, manganese, iron, and cobalt subgroups can be prepared when the metals are stabilized in a low-valent state by ligands such as carbon monoxide and the cyclopentadienyl anion. The wide variety of hydrocarbons which form complexes includes olefins, conjugated and nonconjugated polyolefins, cyclic polyolefins, and acetylenes. 

Substituted cyclopentadienones react with iron carbonyls to form stable, diamagnetic 7r-co triplexes of the type [Fe(CO)3(cyclopentadienone)] (215). The proposed structure is shown in (XX). These complexes undergo reactions typical of metal carbonyls, e.g., displacement of carbon monoxide by tertiary phosphines, but the carbonyl group of the ligand does not show reactions characteristic of a keto-group. These complexes are also formed by interaction of acetylenes with iron carbonyls (see Section VI,C). Interaction of tetracyclone and Fe3(CO)i2 gives unstable complexes which contain the sandwich anion [Fe(tetracyclone)2]2 analogous to the anion (XXV) (215). 

Another carbon anion you may have met is the acctylidc ion, formed by the action of strong base on acetylene ... 

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