Hydrogenation nitrogen-containing heteroaromatic

Finally, polymer 594 has been used as an arene-catalyst to activate nickel from nickel(II) chloride and lithium, in order to perform hydrogenation of different organic substrates such as afkenes, afkynes, carbonyl compounds and their imines, alkyl and aryl halides (chlorides, bromides and iodides), aromatic and heteroaromatic compounds as well as nitrogen-containing systems such as hydrazines, azoxy compounds or Af-amino oxides, giving comparable results to those obtained in the corresponding reaction in solution . 

The hydrogenation of N-heteroaromatic compounds is of interest in relation to HDN, since selective hydrogenation of the nitrogen-containing rings always takes place prior to C-N bond breaking (see Scheme Few... 

Applications of asymmetric hydrogenation of several heteroaromatic nitrogen-containing substrates for the installation of chirogenic centers, and therefore enantioselective preparation of important precm ors and intermediates, as well as their use in the total syntheses of some bioactive natural compounds, are discussed below. 

Perfluorinated systems are molecules in which all of the hydrogen atoms have been replaced by fluorine and so, in this chapter, we are concerned with the chemistry of perfluorinated heteroaromatic systems containing one or more nitrogen atoms such as pentafluoropyridine, tetrafluoropyrimidine, and trifluoro- -triazine. Since the first realistic synthesis of pentafluoropyridine was reported in the 1960s, the chemistry of perfluorinated heteroaromatic systems has developed extensively and been discussed in several detailed reviews and in more general monographs. 

Polyazines are polymers with six-membered heteroaromatic rings in the main chain, whereby these rings contain at least one tertiary nitrogen. Compounds which can be conceived by partial hydrogenation of the hetero rings are related to these. Of the very great number of possible different compounds, those with quinoxaline (I), quinazoline dione (II), triazine (III), melamine (IV), and isocyanurate (V) groups have found use in industry ... 

Heterocyclic aromatic compounds contain C and H atoms other than carbon and hydrogen (Fig. 6). For the monocyclic molecules Hiickel s rule is applicable. For example both pyridine and pyrrole contain six ti electrons. Unlike the former the lone pair of the latter is delocalized. Armit and Robinson have shown a connection between the electronic sextet and the heteroaromaticity. Due to the electronegativity difference between carbon and nitrogen the bonds in pyridine are not of equal length and the delocalization is not perfect. Five membered heteroaromatics with oxygen and sulfur are furan and thiophene respectively. Pyrazole/imidazole, triazoles and tetrazoles are five membered heteroaromatics with two, three and four nitrogen atoms respectively. Three important aromatic six membered heterocyclic molecules are pyrimidine, pyrazine and pyridazine. Benzofused... 

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