C = N groups

Asymmetric aryl isocyanate dimers, ia which the C=0 group of oae molecule reacts with the C=N group of another, have been postulated as labile iatermediates ia the formation of carbodiioiides (17) upoa heating isocyanates. 

The Cg-amine, originally obtained by the methanolysis of kasugamycin, on treatment with lead tetraacetate or sodium periodate afforded a nitrile amine, with evolution of carbon dioxide, showing a maximum at 2200 cm.-1. This reaction is explained only by the structure (13). The -N-C=N group of the product can be formed by oxidative decarboxylation and can be easily rationalized by the present understanding of such reagents (2, 13) as shown below. On the other hand, the treatment... 

Pascal An SI unit of pressure the pressure exerted by the force of 1 newton on an area of 1 square meter, 104,635 Paschen series, 138 Pasteur, Louis, 601 Pauli exclusion principle, 141-143 Pauling, Linus, 185 Pentyl propionate, 596t Peptide linkage The—C—N—group... 

Our sincere appreciation goes to all the members of the K. C.N. group whose dedication, brilliance, and diverse ethnic background have made this group s contributions both possible and enjoyable. 

Phenols, alkali225, and some other substances226-228 serve as initiators of these reactions. In the case of poly(acrylonitrile) this role is played by a tertiary hydrogen which is activated by the C=N group. 

Much earlier information on the structure of diazonium ions than that derived from X-ray analyses (but still useful today) was obtained by infrared spectroscopy. The pioneers in the application of this technique to diazonium and diazo compounds were Le Fevre and his school, who provided the first IR evidence for the triple bonds by identifying the characteristic stretching vibration band at 2260 cm-1 (Aroney et al., 1955 see also Whetsel et al., 1956). Its frequency lies between the Raman frequency of dinitrogen (2330 cm-1, Schrotter, 1970) and the stretching vibration frequency of the C = N group in benzonitrile (2255 cm-1, Aroney et al., 1955). In substituted benzenediazonium salts the frequency of the NN stretching vibration follows Hammett op relationships. Electron donor substituents reduce the frequency, whereas acceptor substituents increase it. The 4-dimethylamino group, for example, shifts it by 103 cm-1 to 2177 cm-1 (Nuttall et al., 1961). This result supports the hypothesis that... 

Another arylation reaction which uses arenediazonium salts as reagents and is catalyzed by copper should be discussed in this section on Meerwein reactions. It is the Beech reaction (Scheme 10-49) in which ketoximes such as formaldoxime (10.13, R=H), acetaldoxime (10.13, R=CH3), and other ketoximes with aliphatic residues R are arylated (Beech, 1954). The primary products are arylated oximes (10.14) yielding a-arylated aldehydes (10.15, R=H) or ketones (10.15, R=alkyl). Obviously the C=N group of these oximes reacts like a C = C group in classical Meerwein reactions. It is interesting that the addition of some sodium sulfite is necessary for the Beech reaction (0.1 to 0.2 equivalent of CuS04 and 0.03 equivalent of Na2S03). 

The hydrolysis of an organic nitrile, a compound containing a —C=N group, in basic solution, is proposed to proceed by the following mechanism. Write a complete balanced equation for the overall reaction, list any intermediates, and identify the catalyst in this reaction. 

This is by far the most used type of primary synthesis for quinoxalines. It usually involves the cyclocondensation of an o-phenylenediamine (or closely related substrate) with a synthon containing an oxalyl [—C(=0)—C(=0)—] or equivalent [e.g., HC(=0)—C=N] grouping. For convenience, discussion of this synthesis is subdivided according to the type of synthon used to produce formally aromatic quinoxalines the formation of similar ring-reduced quinoxalines (mostly from related synthons at a lower oxidation state) is included in each such category. 

The amount of the resonance stabilization is similar to that for the benzyl radical. In radicals formed from monomers having C=0 or C=N groups conjugated with the carbon-carbon double bonds, the corresponding resonance structures... 

A product, 14, was also isolated from the reaction between 6,6-Me2AH and cis-[ReCl4(MeCN)2]. X-ray crystallography identified this as 14 resulting from insertion of the C = N group into the adenine N9-H bond [Re N3 2.351 A], Formation of 14 is explained by activation of the coordinated MeCN towards intramolecular nucleophilic attack by the deprotonated adeninyl N9. 

The UV-Vis spectra of the noncoordinated 5-amino-37/-l,3,4-thiadiazole-2-thione 26 and its organotin(iv) complex exhibit two absorption bands at 256 and 318 nm assigned to the 7t-7t and n-jt transitions of the C=N chromophore, respectively <2006SAA148>. These bands undergo a hyperchromic shift upon complexation supporting the participation of the C=N group in the coordination. 

I.3.4.2.4. Heterocumulenes The 1,3-dipolar cycloaddition of substituted ben-zonitrile oxides to the C=N group of chlorocarbonyl isocyanate C1C(0)N=C=0 gives 3-aryl-4-chlorocarbonyl-5-oxo-4,5-dihydro-l,2,4-oxadiazoles 172 in 75%-80% yield (340). A similar reaction with chlorosulfonyl isocyanate, C1S02N=C=0, affords 4-unsubstituted oxadiazolinones 173 (341). 

Prior to 1958 only nitrile-adducts were reported to result from the reaction of nitriles with trihaloboranes (c.f. 36)). The first reported example of the 1,2-addition of boron-halogen bonds to a C=N group involves the reaction of tri-fluoroacetonitrile with trichloroborane or tribromoborane 4) and leads to dimeric derivatives. A 1 1 ratio of the cis-trans isomers is obtained as indicated on the basis of 19F n.m.r. studies. 

A B-Cl bond of pentafluorophenyldichloroborane adds quantitatively across the C=N group of trichloroacetonitrile and yields an equilibrium mixture of the monomeric and dimeric iminoborane derivative 26>. In contrast, benzon-itrile does not react at all with trichloroacetonitrile under comparable conditions 26 ... 

Addition of B—F bonds across C=N groups has never been achieved. Therefore, the only B-fluoro substituted iminoborane so far known was obtained by the reaction of diphenylketimine-lithium with trifluoroborane 13> according to the general Equation (25). 

The following sections provide an overview on the state of the art for the enantioselective hydrogenation (including transfer hydrogenation) of various classes of C = N groups, together with a short, critical assessment of the presently known catalytic systems. Only selective (ee >80%) or otherwise interesting catalysts are included and, furthermore, other reduction methods for C = N functions (hydride reduction, hydrosilylation) are only covered summarily. 

Hydride reductions of C = N groups are well known in organic chemistry. It was therefore obvious to try to use chiral auxiliaries in order to render the reducing agent enantioselective [88]. The chiral catalyst is prepared by addition of a chiral diol or amino alcohol, and the active species is formed by reaction of OH or NH groups of the chiral auxiliary with the metal hydride. A major drawback of most hydride reduction methods is the fact that stoichiometric or higher amounts of chiral material are needed and that the hydrolyzed borates and aluminates must be disposed of, which leads to increased costs for the reduction step. 

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