Nitrogen heterocycles, anionic

Ruonne atoms in aromatic nitrogen heterocycles are readily replaced by oxygen nucleophiles [77] Bistnfluoromethyl hydroxylarmne anion is an mterest-ing nucleophile for the mtroduction of oxygen mto perfluoropyndine Rearrangement of the product occurs at 125 °C [18] (equation 12)... 

Heteroaromatic Annulation with Cyclic Azaallyl Anions Synthesis of Bridgehead Nitrogen Heterocycles... 

The azaallyl anions 85.11-85.17 derived from cyclic nitrogen heterocycles generally react with 6 to afford the corresponding bridgehead nitrogen heterocycles. Some of the examples studied by our group are described below. 

Figure 19 the carbon-13 chemical shifts for a number of nitrogen heterocycles and their anions and cations are plotted against the proton shifts at the same positions. The scatter is excessive, and is not restricted to positions alpha to nitrogen (open circles). In Figure... 

Nitrogen heterocycles continue to be valuable reagents and provide new synthetic approaches such as NITRONES FOR INTRAMOLECULAR -1,3 - DIPOLAR CYCLOADDITIONS HEXAHYDRO-1,3,3,6-TETRAMETHYL-2,l-BENZISOX AZOLINE. Substituting on a pyrrolidine can be accomplished by using NUCLEOPHILIC a - sec - AM IN O ALKYL ATION 2-(DI-PHENYLHYDROXYMETHYL)PYRROLIDINE. Arene oxides have considerable importance for cancer studies, and the example ARENE OXIDE SYNTHESIS PHENANTHRENE 9,10-OXIDE has been included. An aromatic reaction illustrates RADICAL ANION ARYLATION DIETHYL PHENYLPHOSPHONATE. 

A general problem in alkylation of nitrogen heterocycles is the regio-chemistry of the corresponding anions. The ratio of N- versus C-alkylation usually depends on reaction conditions PTC strongly favors N-alkylation. 

A variety of five-membered nitrogen heterocycles can be prepared efficiently by inter- or intramolecular addition/cyclizations of sulfonamide anions with alkynyliodonium salts. The intermolecular variant employs the combination of the amides 172 or anilides 174 with propynyl(phenyl)iodonium triflate (Scheme 65) [131,132]. The yield of dihydropyrroles 173 in this cyclization is extremely sensitive to the nature of the protective group P the tosyl group in 172 proved... 

Nitrogen heterocycles more electrophilic than benzene are susceptible to attack by hydride ion from a complex metal hydride anion. In protic solvents the intermediate cyclic enamines can undergo further reduction. The proper choice of reducing agent and reaction conditions thus allows the preparation of many partially reduced nitrogen heterocycles unavailable by other routes. These reduction procedures provide a valuable adjunct to catalytic hydrogenation155 for the syntheses of saturated nitrogen heterocycles. 

The development of intramolecular anionic cyclization for the preparation of heterocyclic systems provides routes to several oxygen and nitrogen heterocycles. Tetrahydro-furans, pyrrolidines144, indohnes145 or indoles146 have been synthesized via intramolecular... 

The synthesis of the allyl ethers in nitrogen heterocyclic systems presents an element of complication in that the allylation could occur on the oxygen atom or the basic nitrogen atom. This is a feature of alkylation of ambident anions.3 However, this applies only when the allylation is effected by reacting the oxo or hydroxy derivative of the compound with an allyl halide in the presence of a base.3 The alternative method is to react the appropriate halo derivative with sodium allyloxide in allyl alcohol. The latter approach provides not only better yields of the allyl ethers but also certainty of the constitution of the ethers obtained. A diagnostic tool in deciding between the 1-allyl derivative and the O-allyl compound that has commonly been employed is the infrared absorption of the amide carbonyl in the case of the former which is clearly absent in the latter. 

The term ionic liquid usually refers to a salt that exists in the liquid state at or around ambient temperatures. An ionic liquid usually consists of a salt where one or both ions are large and the cation has a low degree of symmetry. These factors tend to reduce the lattice energy of the crystalline form of the salt, and hence lower its melting point. Ionic liquids have an organic cation (often a nitrogen heterocycle) and an inorganic anion. 

In contrast to the neutral molecule of imidazole, the conjugate base is highly susceptible to electrophilic attack, particularly on one or other of the annular nitrogen atoms. Thus, alkylation occurs very rapidly in basic medium. There are also some electrophilic substitution reactions at ring carbon atoms which involve the heterocyclic anion, e.g. diazo coupling and iodination. 

Mercapto or methylthio nitrogen heterocycles are either obtained by direct treatment of hydroxy-nitrogen heterocycles with reagents such as phosphorus pentasulfide or Lawesson reagent (78BSB223 79T2433), or by treatment of activated intermediates such as chloro-nitrogen heterocycles with mercaptide anions as well as by total synthesis. 

Applications of thin-layer and paper chromatography are assodated with many aspects of experimentation in chemistry, biochemistry, pharmacy, medidne, and biology. Extensive tables of Rf values are summarized in the Handbook of Chromatography. They include data for alcohols, alkaloids, amines, amino adds, carboxylic adds, inorganic anions and cations, nitrogen heterocyclics, nucleic... 

The mechanism of this last reaction may be postulated as shown in Scheme 52. Here, the initial nucleophilic attack by the sulfonamide anion (129) is followed by protonation of the intermediate and attack by the chloride anion to yield two moles of the sulfamoyl chloride (125). A wide range of sulfamoyl derivatives can be prepared by nucleophilic displacement of the chlorine atom in sulfamoyl chlorides (125). Examples include condensations with ureas, alcohols, compounds containing acidic hydrogens and nitrogen heterocycles to give the corresponding sulfamoyl derivatives (130)-(133) (Scheme 53). 

In 1975 the anion of T was observed in a mass spectrometer, indicating a positive valence-state Ea for T. In 1990 the Ea of AGCUT were predicted using substitution, replacement, and conjugation effects [10-14], In order to estimate the Ea of substituted compounds, that of the parent compounds is required. In 1974 I. Nenner and G. J. Schulz estimated the AEa of quinoline (0.36 eV), pyradazine (0.40 eV), pyrimidine (0.00 eV), pyrazine (0.40 eV), and s-triazine (0.45 eV) from electron transmission spectra and half-wave reduction potentials [15]. No adiabatic electron affinities of aromatic nitrogen heterocyclic compounds were measured in the gas phase before 1989 [16]. 

---