Cyanide ion as nucleophile

Rate constants for the substitution reactions of square-planar dithio-phosphates and dithiocarbonate complexes of Ni(II), Pd(II), and Pt(II), with ethylenediamine and cyanide ion as nucleophiles, have been measured in methanol. The results were compared with those obtained in previous investigations, and interpreted in terms of the stabilities of 5-coordinate species that are formed prior to substitution (377). 

The masterlist is divided by reaction polarity as well as by the acceptable skeletal level of the a-carbon (the construction site). Thus cyanide ion as nucleophile (Dx) cannot be used to attach a chain of carbons in one construction it is limited to [Pg.72]

In the presence of methanol as solvent and 1,4-dicyanobenzene as acceptor, photoinduced electron transfer from 1,4-bis(methylene)cyclohexane gives 4-(methoxymethyl)-1 -methylenecyclohexane and 4-(4-cyanophenyl)-4-(methoxy-methyl)-l-methylenecyclohexane which arise by nucleophilic attack of the solvent on the radical cations, followed either by reduction and protonation, or by combination with the radical anion of the electron acceptor.These observations are in accordance with the proposed mechanism of the nucleophile-olefin combination, aromatic substitution (photo-NOCAS) reaction. The same group has also investigated the use of cyanide ion as nucleophile and report that irradiation of a mixture of 1,4-dicyanobenzene in the presence of biphenyl as donor, KCN, and 18-crown-6 gives a mixture of (79) and (80). These workers have also extended the scope of NOCAS to fluoride ion. In particular, use of 2,3-dimethylbut-2-ene and 2-methylbut-2-ene gives 4-cyanophenyl substituted... 

Table 2 Electrochemical characteristics for a-complexes and reaction products with the cyanide ion as nucleophile...

Figure 3-22 shows a nucleophilic aliphatic substitution with cyanide ion as a nucleophile, i his reaction is assumed to proceed according to the S f2 mechanism with an inversion in the stereochemistry at the carbon atom of the reaction center. We have to assign a stereochemical mechanistic factor to this reaction, and, clearly, it is desirable to assign a mechanistic factor of (-i-1) to a reaction with retention of configuration and (-1) to a reaction with inversion of configuration. Thus, we want to calculate the parity of the product, of 3 reaction from the parity of the... 

Cyanide ion ( C = N ) The negatively charged carbon atom of cyanide ion IS usually the site of its nucleophilic character Use of cyanide ion as a nucleophile permits the extension of a carbon chain by carbon-carbon bond formation The product is an alkyl cyanide or nitrile... 

Of the halogens, the fluoro-substituent is a favourite in photosubstitution (c/. Section 2). It shows a curious selectivity in that as a rule it is not easily substituted by cyanide ion, a nucleophile that functions so well with other leaving groups. 

The most frequently used method for the preparation of isoquinoline Reissert compounds is treatment of an isoquinoline with acyl chloride and potassium cyanide in water or in a dichloromethane-water solvent system. Though this method could be successfully applied in a great number of syntheses, it has also some disadvantages. First, the starting isoquinoline and the Reissert compound formed in the reaction are usually insoluble in water. Second, in the case of reactive acyl halides the hydrolysis of this reaction partner may became dominant. Third, the hydroxide ion present could compete with the cyanide ion as a nucleophile to produce a pseudobase instead of Reissert compound. To decrease the pseudobase formation phase-transfer catalysts have been used successfully in the case of the dichloromethane-water solvent system, resulting in considerably increased yields of the Reissert compound. To avoid the hydrolysis of reactive acid halides in some cases nonaqueous media have been applied, e.g., acetonitrile, acetone, dioxane, benzene, while utilizing hydrogen cyanide or trimethylsilyl cyanide as reactants instead of potassium cyanide. 

An Sn2 displacement constitutes the key operation in which the ester group at C-3 of catharanthine is introduced [62], Thus, a contrapolarizing change of the 11-position from d to a allows the desired reaction to be performed, using cyanide ion as the nucleophile. 

The first such process was realized over one and a half centuries ago with the discovery of the Strecker reaction [10] which has a cyanide ion as the nucleophile, leading to the formation of a-amino nitriles 10 (Scheme 7.2). These highly versatile synthetic intermediates can be hydrolyzed to a-amino acids or can be converted to other molecules [11, 12]. 

The use of acetylides as nucleophiles is a particularly important example of nucleophilic substitution because it results in a new carbon-carbon bond. Thus, larger organic molecules can be assembled from smaller ones using this method. The same is true for cyanide ion as a nucleophile (part b). 

The same disconnection 41 can be used for carboxylic acids with CO2 as the electrophile for a Grignard reagent 40. Dry ice (solid CO2) is particularly convenient for these reactions. Switching polarity by FGI to the nitrile 42, the same disconnection now uses cyanide ion as the nucleophile but the same alkyl halide 39 that was used to make the Grignard reagent. Mechanistic considerations should decide between these alternatives. 

The use of cyanide ion as a nucleophile in an SN2 reaction (see Section 10.8), followed by hydrolysis of the product nitrile, provides a useful preparation of carboxylic acids that contain one more carbon than the starting compound ... 

This reaction is presented in a style with which you will become familiar. The organic starting material is written first and then the reagent over the reaction arrow and the solvent under it. We must decide what happens. NaCN is an ionic solid so the true reagent must be cyanide ion. As it is an anion, it must be the nucleophile and the carbonyl group must be the electrophile. Let us try a mechanism. 

The reaction of an alkyl halide with cyanide ion involves nucleophilic substitution (Sec. 14.5). The fact that HCN is a very weak acid tells us that cyanide ion is a strong base as we might expect, this strongly basic ion can abstract hydrogen ion and thus cause elimination as well as substitution. Indeed, with... 

Step 1 The negatively charged carbon of cyanide ion is nucleophilic and bonds to the carbonyl carbon of the aldehyde or ketone. Hydrogen cyanide itself is not very nucleophilic and does not ionize to form cyanide ion to a significant extent. Thus, a source of cyanide ion such as NaCN or KCN is used. 

At first glance the conversion of bromobenzene to benzenenitrile looks simple—just carry out a nucleophilic substimtion using cyanide ion as the nucleophile. Then we remember that bromobenzene does not undergo either an S l or an 5 2 reaction (Section 6.14A). The conversion can be accomplished, however, though it involves several steps. Oudine possible steps. 

If we use cyanide ion as the nucleophile (entry 14 in Table 6.1), the alkyl halide must have the halogen (Cl, Br, or I) attached to a propyl group. The... 

A new synthesis of aldehydes with 2-methyl-2-thiazoline has the advantage of releasing the aldehydes from the thiazolidine intermediate under neutral conditions . Acetylene derivatives can be obtained from aldehydes via dibromomethylene compounds Novel reactions of alkynes with cationoid electrophiles have been published. -Diketones and 2-ketoalkoximes can be obtained by this reaction from acid chlorides and aliphatic nitro compounds respectively Addition of aldehydes to activated carbon-carbon double bonds occurs smoothly in the presence of cyanide ions as catalysts . Poly- -carbonyl compounds have been prepared by condensation of two anions, whereby the enolate salt of a y8-keto ester condenses as an electrophilic anion with strong nucleophiles such as the dianion of benzoylacetone. ... 

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