Nucleophiles cyanide

The mechanism of this reaction is outlined m Figure 17 8 It is analogous to the mech anism of base catalyzed hydration m that the nucleophile (cyanide ion) attacks the car bonyl carbon m the first step of the reaction followed by proton transfer to the carbonyl oxygen in the second step... 

Nucleophilic substitution of the chlorine atom in 2-chloropyrazine and 2-chloroquinoxa-lines has been effected with a variety of nucleophiles, including ammonia and amines, oxygen nucleophiles such as alkoxides, sodium azide, hydrazine, sulfur containing nucleophiles, cyanide, etc., and reactions of this type are typical of the group (see Chapter 2.02). 

Aldehydes and unhindered ketones undergo a nucleophilic addition reaction with HCN to yield cyanohydrins, RCH(OH)C=N. Studies carried out in the early 1900s by Arthur Eapworth showed that cyanohydrin formation is reversible and base-catalyzed. Reaction occurs slowly when pure HCN is used but rapidly when a small amount of base is added to generate the nucleophilic cyanide ion, CN. Alternatively, a small amount of KCN can be added to HCN to catalyze the reaction. Addition of CN- takes place by a typical nucleophilic addition pathway, yielding a tetrahedral intermediate that is protonated by HCN to give cyanohydrin product plus regenerated CN-. 

Tkn assay using the hard nucleophile cyanide was described in Section 7.5.1.2, where non-radiolabeled KCN was used to detect the presence of cyanide adducts using mass spectrometry. However, by using K CN, it is possible to make this a quantitative assay by assessing the amount of cyanide incorporated into a non-radiolabeled test... 

Some carhon-carbon bond forming reactions with carbon nucleophiles cyanide ion, acetylide ion and Grignard reagents. 

SAMPLE SOLUTION (a) Sodium cyanide is a source of the nucleophilic cyanide anion. Cyanide ion attacks ethylene oxide, opening the ring and forming 2-cyanoethanol ... 

Write out the structure of the starting material. Notice that it contains a primary bromide and a primary chloride. Bromide is a better leaving group than chloride and is the one that is displaced faster by the nucleophilic cyanide ion. 

The structure of the chloride-cyanide stannate 39b is unusual in that the strongly nucleophilic cyanide would exhibit N-bonded coordination to Sn rather than a C-bonded orientation219. 

The anodic cyanation reaction allows the direct installation of cyanide without leaving groups. The cyanide acts in the electrochemical conversion similar to fluoride. After oxidation of the organic substrate the nucleophilic cyanide enters the reaction scene forming a less electron rich product which is deactivated for further anodic conversions. Therefore, the electrochemical cyanation reaction has some significance for aromatic substrates [67] (Scheme 12). 

The first of these carbon nucleophiles, cyanide ion, is a moderate base and a good nucleophile ... 

Nucleophilic cyanide ion can also be used to open the epoxide ring. This reaction was employed in a now obsolete pathway for the preparation of acrylonitrile, which is used to make Orion ... 

The HOMO of the nucleophile will depend on what the nucleophile is, and we will meet examples in which it is an sp or sp3 orbital containing a lone pair, or a B-H or metal-carbon o orbital. We shall shortly discuss cyanide as the nucleophile cyanide s HOMO is an sp orbital on carbon. 

Similar ring-contractions have been accomplished by treatment of a dithiolane with tris(A A -diethylamino) phosphine.l,2-Dithiolane-4-one, however, gave only polymeric material. The reaction proceeds by thiophilic attack by the nucleophilic cyanide or phosphine ... 

The silyl cyanide is an electrophile while the cyanide ion in the catalyst is a nucleophile. Cyanide adds to the carbonyl group and the oxyanion product is captured by silicon so liberating another cyanide ion for the next cycle. 

On the other hand, the adducts with a carbon-carbon linkage, e.g. 6-cyanodihydrobenzophenanthridines (Scheme 1, Nu = CN) are rather re-sistent to acids. A number of reactions with carbon nucleophiles (cyanide, Grignard reagent, nitromethane, acetone, butanone, acetaldehyde) are known and weU documented in the literature [8], Only a little is known about QBA reactions with oxygen, nitrogen, and sulfur nucleophiles [8]. 

As predicted, the soft nucleophile cyanide anion reacts with 1-chloroalkyl carbonates to afford 1-cyanoalkyl carbonates in good yields as shown with the example depicted in scheme 77. 

Mechanisms which predict parallel increases in the activity of the isomers do not appear tenable. However, realizing that the second step (k i) competes with isomerizations (ka-j) and that once the very nucleophilic cyanide is attached to the iron center, it is even more tenacious than the mphen ligand, the ka-j path stereochemistry can be summarized as shown in Table IV. 

A shorter and neater synthesis of (+ )-dihydrogambirtannine involved the multiple-phase reduction of the isoquinolinium salt 78 with sodium borohydride in a methanol-ether—water system in the presence of a high concentration of cyanide ion. The intermediate, presumably the cyanide (79) formed by trapping of the initially generated dihydroisoquinoline derivative by nucleophilic cyanide ion, was not isolated but was converted directly into ( )-dihydrogambirtannine (67) by heating in dilute hydrochloric acid. Dehydrogenation of the stable hydrochloride of 67 by means of iodine and sodium acetate afforded an improved route... 

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