Benzo quinolines formation

It would be expected that the stabilization of the adsorbed species by an extended conjugated system should increase with the number of aromatic rings in the adsorbed azahydrocarbon. However, data suitable for comparison are available only for phenanthridine, benzo-[/]quinoline, and benzo[h] quinoline. The large difference in the yields of biaryl obtained from the last two bases could be caused by steric interaction of the 7,8-benz-ring with the catalyst, which would lower the concentration of the adsorbed species relative to that with benzo[/]quinoline. The failure of phenanthridine to yield any biaryl is also noteworthy since some 5,6-dihydrophenanthridine was formed. This suggests that adsorption on the catalyst via the nitrogen atom is possible, but that steric inhibition to the combination of the activated species is involved. The same effect could be responsible for the exclusive formation of 5,5 -disubstituted 2,2 -dipyridines from 3-substi-tuted pyridines, as well as for the low yields of 3,3, 5,5 -tetramethyl-2,2 -bipyridines obtained from 3,5-lutidine and of 3,3 -dimethyl-2,2 -... 

The sonochemistry of the other alkali metals is less explored. The use of ultrasound to produce colloidal Na has early origins and was found to greatly facilitate the production of the radical anion salt of 5,6-benzo-quinoline (225) and to give higher yields with greater control in the synthesis of phenylsodium (226). In addition, the use of an ultrasonic cleaning bath to promote the formation of other aromatic radical anions from chunk Na in undried solvents has been reported (227). Luche has recently studied the ultrasonic dispersion of potassium in toluene or xylene and its use for the cyclization of a, o-difunctionalized alkanes and for other reactions (228). 

Benzol/] quinolines formation of, 150, 162 metal catalysts, action on, 189, 196 Benzol/i]quinoline, metal catalysts, action on, 189, 196 Benzoselenazole, 2-amino-, 68 Benzoselenazole-2-thione, 62 Benzoselenazol-2-one, 49 Benzo-1,2,4-thiadiazin-3-ones, methyla -tion of, 259 Benzothiazoles 2-acylamino-, 77... 

In contrast with the azoles, diazoles and their benzo derivatives tend to react with dichlorocarbene to yield the tris(diazolyl)methanes, presumably via the initial formation of the N-dichloromethyl derivative [6, 13]. Only in more activated polymethyl derivatives does reaction occur at a ring carbon atom. In a similar manner (7.7.1.B), 2-chloropyridine and 2-chloroquinoline react with dichlorocarbene at the ring nitrogen atom to yield, after nucleophilic displacement of the chloro group, the 1 -dichloromethyl-2-oxo derivatives (13-25%) [14] (Scheme 7.38). 2-Chlorobenzothiazole reacts in an analogous manner, but other pyridine and quinoline derivatives fail to react. It is also noteworthy that the dichloromethyl group is unusually stable and is not converted into the formyl group. 

Oxidation of quinoline and isoquinoline under vigorous conditions with potassium permanganate results in oxidative degradation of the benzo-fused ring and formation of pyridine-2,3- and -3,4-dicarboxylic acid respectively. As expected, the presence of electron-donating substituents facilitates the reaction while electron-withdrawing substituents make oxidation much more difficult. Apart from A-oxide formation, little study has been devoted to the oxidation of other benzo-fused 7r-deficient systems. 

An alcoholic solution of 2,4-diphenylbenzo (g) quinoline (CVII) is stable on irradiation, but on addition of a few drops of sulfuric acid, photodehydrogenation takes place with the formation of the cyclized 4-phenyl-l, 2-benzo-r>-azapyrene126 (CVIII). 

Nucleophilic attack at ring carbon occurs in benzenes only when electron-withdrawing substituents are present. Even with pyridine, only the strongest nucleophiles react. This is because the formation of the initial adduct (2) involves de-aromatization of the pyridine ring and, once formed, many such adducts tend to re-aromatize by dissociation (1 2). Benzo fusion decreases the loss in aromaticity for the formation of the adduct and thus quinoline (3) and especially acridine (4) react more readily with nucleophiles. 

Intramolecular replacement of fluorine by nitrogen has been used for the formation of fused heterocycles, i.e. derivatives of indole,187 - 189 2,3-dihydroindole.190 benzopyrazole.191 benzo-pyridazine,192 benzoxazine,193194 bcnzothiadiazole,193 quinoline,196-198 and benzothiazinc (e.g., 9).194 1"-200... 

In some cases the reaction is accompanied by a five-membered heterocyclic ring closure. For example, l-nitro-4-methoxynaphthalene 265 reacts with p-tolylpro-penylsulfone to give benzo[/z]quinoline 266 (35%) together with A-hydroxybenzo-pyrrole derivative 267 (14%) (Scheme 77) (00EJO521). Annulation of the pyridine ring may proceed via anion 268, whereas the formation of benzoindole 267 occurs via neutral alkene 269. 

This review deals with the formation of reduced pyridines and their benzo analogs from the parent heteroaromatic bases. Included are acridines, isoquinolines, pyridines and quinolines and their quaternary ammonium salts and N-oxides. The formation of the reduced species by other methods, e.g. Hantzsch dihydropyridine synthesis, is not addressed. 

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