Quinolines, nucleophilic aromatic

Recently37, the importance of CT complexes in the chemistry of heteroaromatic N-oxides has been investigated in nucleophilic aromatic substitutions. Electron acceptors (tetracyanoethylene and p-benzoquinones) enhance the electrophilic ability of pyridine-N-oxide (and of quinoline-N-oxide) derivatives by forming donor-acceptor complexes which facilitate the reactions of nucleophiles on heteroaromatic substrates. 

Chloropyrazolo[3,4- ]quinoline, 3-chloropyrazolo[3,4-acid-induced nucleophilic aromatic substitution (SnH) of H-3 in A -hydroxypyrazolo[3,4-first cases of nucleophilic aromatic substitution of a fused pyrazole <2002JOC585>. 

Nucleophilic aromatic substitution of hydrogen in syntheses of quinoline derivatives 01H(54)445. 

If the aromatic moiety of a cinnamylamine derivative has an ort/io-halogen substituent, 1,2-dihydroquinoline would be obtained yia the subsequent S Ar reaction. In the presence of catalytic amounts of tosylamide, MBH adduct 603 was rearranged to the thermodynamically more stable tosylamide derivative, which then could be easily subjected to nucleophilic aromatic substitution reaction at the ortho position, giving 1,2-dihydroquinoline 605 in 81% yield. Furthermore, using DBU as a base, elimination of p-toluenesulfinic acid afforded quinoline 606 in 69% yield (Scheme 4.178). However, interestingly, Xn-substituted MBH adducts 607 were directly converted into quinolines 608 in a one-pot reaction in moderate yields. The discrepancy between 604 and 607... 

These systems nitrate aromatie eompounds by a proeess of electro-philie substitution, the eharacter of whieh is now understood in some detail ( 6.1). It should be noted, however, that some of them ean eause nitration and various other reactions by less well understood processes. Among sueh nitrations that of nitration via nitrosation is especially important when the aromatic substrate is a reactive one ( 4.3). In reaetion with lithium nitrate in aeetie anhydride, or with fuming nitrie aeid, quinoline gives a small yield of 3-nitroquinoline this untypieal orientation (ef. 10.4.2 ) may be a eonsequenee of nitration following nucleophilic addition. ... 

A variety of aryl systems have been explored as substrates in the Knorr quinoline synthesis. Most notable examples are included in the work of Knorr himself who has demonstrated the high compatibility of substituted anilines as nucleophilic participants in that reaction. In the case of heteroaromatic substrates however, the ease of cyclization is dependent on the nature and relative position of the substituents on the aromatic ring." For example, 3-aminopyridines do not participate in ring closure after forming the anilide... 

To derive the maximum amount of information about intranuclear and intemuclear activation for nucleophilic substitution of bicyclo-aromatics, the kinetic studies on quinolines and isoquinolines are related herein to those on halo-1- and -2-nitro-naphthalenes, and data on polyazanaphthalenes are compared with those on poly-nitronaphthalenes. The reactivity rules thereby deduced are based on such limited data, however, that they should be regarded as tentative and subject to confirmation or modification on the basis of further experimental study. In many cases, only a single reaction has been investigated. From the data in Tables IX to XVI, one can derive certain conclusions about the effects of the nucleophile, leaving group, other substituents, solvent, and comparison temperature, all of which are summarized at the end of this section. 

On the basis of the reaction of alkyl radicals with a number of polycyclic aromatics, Szwarc and Binks calculated the relative selectivities of several radicals methyl, 1 (by definition) ethyl, 1.0 n-propyl, 1.0 trichloromethyl, 1.8. The relative reactivities of the three alkyl radicals toward aromatics therefore appears to be the same. On the other hand, quinoline (the only heterocyclic compound so far examined in reactions with alkyl radicals other than methyl) shows a steady increase in its reactivity toward methyl, ethyl, and n-propyl radicals. This would suggest that the nucleophilic character of the alkyl radicals increases in the order Me < Et < n-Pr, and that the selectivity of the radical as defined by Szwarc is not necessarily a measure of its polar character. 

Further new competitive AMPA antagonists include the imidazo-fused 23-benzodiazepine derivative 103. This compound showed excellent anticonvulsant activity and other activities indicative of possible therapeutic significance in human stroke and Parkinson k disease <00BMC2127>. An efficient synthesis of fluorine-containing H-1,4-diazepino[6,5-/t]quinolines has been described based on iV,/V-dimethyl-5,7-bis(trifluoroacetyl)-8-quinolylamine and an aromatic nucleophilic displacement with 1,2-ethylenediamine, followed by cyclocondensation <00S1822>. 

One aspect of asymmetric catalysis has become clear. Every part of the molecule seems to fulfill a role in the process, just as in enzymic catalysis. Whereas many of us have been used to simple acid or base catalysis, in which protonation or proton abstraction is the key step, bifunctional or even multifunctional catalysis is the rule in the processes discussed in this chapter.Thus it is not only the increase in nucleophilicity of the nucleophile by the quinine base (see Figures 6 and 19), nor only the increase in the electrophilicity of the electrophile caused by hydrogen bonding to the secondary alcohol function of the quinine, but also the many steric (i.e., van der Waals) interactions between the quinoline and quinuclidine portions of the molecule that exert the overall powerful guidance needed to effect high stereoselection. Important charge-transfer interactions between the quinoline portion of the molecule and aromatic substrates cannot be excluded. 

Unsaturated 5(4//)-oxazolones derived from aromatic and heterocyclic aldehydes including phthalic anhydride/ antipyrine/ " chromone/ indoles/ pyridines/" ° quinolines/" diazines/" benzoxazoles/" and benzimidazoles " " have been prepared. Reaction with nitrogen nucleophiles and subsequent cycliza-tion leads to the expected 5(477)-imidazolones. 

Nucleophilic reagents attack pyridine at the a-position to form an adduct that rearomatizes by dissociation (Scheme 1). Only very strong nucleophiles, e.g. NH2-, RLi, LAH, Na-NH3, react, and for the second step to afford a substitution product (5), conditions that favour hydride loss are required. Adducts formed with hydride ions (from LAH) or carbanions (from lithium alkyls) are relatively more stable than the others at low temperature, and dihydropyridines (6) can be obtained by careful neutralization. Fusion of a benzene ring to pyridine increases reactivity towards nucleophiles, and attack is now found at both a- and y-positions in quinoline (7) and at C-l in isoquinoline (8). This may be attributed to a smaller loss of aromaticity in forming the initial adduct than in pyridine, and thus a correspondingly decreased tendency to rearomatize is also observed. Acridine reacts even more easily, but nucleophilic attack is now limited to the y -position (9), as attachment of nucleophiles at ring junctions is very rare. 

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. 

Quinolines have also been prepared on insoluble supports by cyclocondensation reactions and by intramolecular aromatic nucleophilic substitution (Table 15.26). Entry 10 in Table 15.26 is an example of a remarkable palladium-mediated cycloaddition of support-bound 2-iodoanilines to 1,4-dienes. Reduction of the nitro group of polystyrene-bound 2-nitro-l-(3-oxoalkyl)benzenes with SnCl2 (Entry 11, Table 15.26) leads to the formation of quinoline /Y-oxides. These intermediates can be reduced to the quinolines on solid phase by treatment with TiCl3. 4-Quinolones have been prepared by thermolysis of resin-bound 2-(arylamino)methylenemalonic esters [311]. 

The presence of N-atoms in the aromatic part of the aldehyde appears essential for chiral amplification. With only one nitrogen, such as in the case of 3-pyridine carbaldehyde, autocatalytic kinetics but no chiral amplification effect has been observed [24,25]. In the case of 3-quinoline carbaldehyde, i.e., in the presence of two nucleophilic centers, autocatalysis as well as moderate chiral amplification were reported [26,27]. Highest amplification capacity is observed in the presence of two N-atoms in the aromatic part of the aldehyde, where for the substituent at the 2-position the amplification capacity increases H < CH3 < f- Bu - C=C -, i.e., with the size and rigidity of this group. So far, detailed studies that could relate the given observations to the possible mechanism of chiral amplification in Soai s reaction are still to be carried out. 

When first reported in 1905, the Reissert reaction demonstrated the addition of KCN to quinoline in the presence of benzoyl chloride, but many new modifications since then have employed other nucleophiles and catalytic promotion by a Lewis acid. Shibasaki reported in 2001 the first catalytic enantioselective Reissert-type reaction. Optimized reaction conditions involving an electron-rich aromatic acid chloride in a low-polarity solvent, and use of catalyst 14, were found to suppress the racemic pathway and resulted in good enantioselectivity (Scheme 2) <2001JA6801>. 

Oxidation of the pyridine nitrogen increases the propensity of the aromatic ring for nucleophilic attack at the 2- and 4-positions. a-Benzotriazolyl-substituted pyridines, quinolines, and isoquinolines may be prepared by treatment of the A -oxide with 1-tosylbenzotriazole in the presence of triethylamine in toluene or xylene under reflux <2001H1703> (Equation 78). 

Nucleophilic Reactions of Aromatic Heterocyclic Bases Heterocyclic aromatic compounds containing a formal imine group (pyridine, quinoline, isoquinoline, and acridine) also react readily with nucleophilic reagents. A dihydro-derivative results, which is readily dehydrogenated to a new heteroaromatic system. Since the nucleophile always attacks the a-carbon atom, the reaction formally constitutes an addition to the C=N double bond. An actual localization of the C=N double bond in aromatic heterocyclic compounds is incompatible with molecular orbital theory. The attack of the nucleophilic reagent occurs at a site of low 77-electron density, which is not... 

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