Imines nitrogen

Replacement of carbonyl oxygen by nitrogen (imines, hydrazones, osazones etc.)... 

The less important double bonds to nitrogen (imines) are very similar but now there is only one lone pair on nitrogen and a second G bond to whatever substituent is on the nitrogen atom. Looking down on the planar structures of alkenes, imines, and ketones we see only the ends of the p orbitals but the rest of the structures are clearly related. 

In both complexes, llb,d, the Pd-I bond trans to the phosphorus atom (Pdl—12 in 11b and Pdl-Il in lid) is longer (0.08 and 0.09 A) than the Pd-I bond trans to the nitrogen atom, which might be attributed to the larger trans influence of the phosphorus compared to nitrogen (imine and pyridine) [45]. In the solid state one of the o-aryl substituents in complex llb,d (methyl in the case of 11b and isopropyl in the case of lid) is oriented above/below the coordination plane. A connection between shielding of the metal center along the z-axis and chain transfer reactions was found for several diimine complexes [22 c, 33 b, 41, 42 c]. 

It ia possible that an unstable di-imine is first formed and rapidly loses nitrogen ArN,+ X- -------------------------> ArN=NH ----------> ArH -f-N,... 

The nucleophilicity of amine nitrogens is also differentiated by their environments. In 2,4,5,6-tetraaminopyrimidine the most basic 3-amino group can be selectively converted to a Schiff base. It is meta to both pyrimidine nitrogens and does not form a tautomeric imine as do the ortho- and /xira-amino groups. This factor is the basis of the commercial synthesis of triamterene. 

Aromatization of indolines is important in completing synthetic sequences in which the directive effects of the indoline ring have been used to achieve selective carbocyclic substitution[l]. Several methods for aromatization have been developed and some of these are illustrated in Table 15.2. A range of reagents is represented. One type of procedure represents use of oxidants which are known to convert amines to imines. Aromatization then provides the indole. Such reagents must not subsequently oxidize the indole. Mereuric acetate (Entry 1) is known to oxidize other types of amines and presumably reacts by an oxidative deprotonation ot- to the complexed nitrogen. 

Step 5 The nitrogen stabilized carbocation is the conjugate acid of the imine Proton transfer to water gives the imine... 

Imines. The group >C=NH is named either by the suffix -imine or by citing the name of the bivalent radical R R C< as a prefix to amine. For example, CH3CH2CH2CH=NH could be named 1-butanimine or butylideneamine. When the nitrogen is substituted, as in CH2=N—CH2CH3, the name is A-(methylidene)ethylamine. 

Quinones are exceptions. When one or more atoms of quinonoid oxygen have been replaced by >NH or >NR, they are named by using the name of the quinone followed by the word imine (and preceded by proper affixes). Substituents on the nitrogen atom are named as prefixes. Examples are... 

Dipolar cycloaddition reactions with azides, imines, and nitrile oxides afford synthetic routes to nitrogen-containing heterocycles (25—30). 

Carbon—nitrogen double bonds in imines, hydrazones, oximes, nitrones, azines, and substituted diazomethanes can be cleaved, yielding mainly ketones, aldehydes and/or carboxyHc acids. Ozonation of acetylene gives primarily glyoxal. With substituted compounds, carboxyHc acids and dicarbonyl compounds are obtained for instance, stearoHc acid yields mainly azelaic acid, and a smaH amount of 9,10-diketostearic acid. 

The first-order decomposition rates of alkyl peroxycarbamates are strongly influenced by stmcture, eg, electron-donating substituents on nitrogen increase the rate of decomposition, and some substituents increase sensitivity to induced decomposition (20). Alkyl peroxycarbamates have been used to initiate vinyl monomer polymerizations and to cure mbbers (244). They Hberate iodine quantitatively from hydriodic acid solutions. Decomposition products include carbon dioxide, hydrazo and azo compounds, amines, imines, and O-alkyUiydroxylarnines. Many peroxycarbamates are stable at ca 20°C but decompose rapidly and sometimes violently above 80°C (20,44). 

Reductions of Nitriles. In the reduction of nitriles, hydrogen is added progressively across the carbon—nitrogen triple bond, forming first the imine and then the amine. 

Alkylation of pyrimidin-2(or 4)-amine on a ring-nitrogen gives an imine, e.g. (8), of quite high basic strength (pjSTa 10.7) because its cation, e.g. (13 R = Me), has typical and effective resonance stabilization indeed, methylation of pyrimidine-2,4-diamine gives a still stronger base (pjSTa> 13) due to an even more resonance-stabilized cation (14). 

Dihydroazoles can exist in at least three forms (cf. Section 4.01.1.3), which in the absence of substituents are tautomeric with each other. The forms in which there is no hydrogen on at least one ring nitrogen normally predominate because imines are generally more stable than vinylamines in aliphatic chemistry. Thus for dihydropyrazoles the stability order is A" (hydrazone) (288) > A (azo) (289) >A (enehydrazine) (290). 

As the sp nitrogen atom in many heterocycles can be alkylated and aminated, the construction of an azomethine ylide or azomethine imine dipole is readily attainable as shown in Scheme 13. These ylides are very reactive and undergo cycloaddition with a... 

In addition to (461), Dorn has described the imine (463) isolated from 5-amino-l-methylpyrazole and arenesulfonyl chloride (80CHE1). Upon heating, or in the presence of triethylamine, it undergoes rearrangement to the more stable 5-bis(arylsul-fonamido)pyrazoles (464). 5-Iminopyrazolines (461) react with acyl chlorides at the exocyclic nitrogen atom to afford amidopyrazolium salts (B-76MI40402). 

Other non-oxidative procedures have also been used to deaminate aziridines. For example, aziridines react with carbenes to yield ylides which subsequently decompose to the alkene. Dichlorocarbene and ethoxycarbonylcarbene have served as the divalent carbon source. The former gives dichioroisocyanides, e.g. (281), as by-products (72TL3827) and the latter yields imines (72TL4659). This procedure has also been applied to aziridines unsubstituted on the nitrogen atom although the decomposition step, in this case, is not totally stereospecific (72TL3827). 

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