Quinolines regioselective

In the case of the 2-dimethylamino- (or 2-amino-)methylene derivatives, the products were at first thought to be pyrimido[4,5-c]isoquinolines (267), but later work with 6-(N-substituted amino)uracils assigned the structures of the products (268) as belonging to the isomeric pyrimido[4,5-f>]quinoline system (74CB2537), in agreement with the regioselection rules above. 

As one might expect, most of the reported cases of Camps quinoline syntheses involve reactions in which only one of the carbonyl groups is enolizable, thus eliminating the regioselectivity problem. 

Skraup proposed a simple mechanism involving imine formation followed by an acid-mediated cyclization. Unfortunately the observed regioselectivity is not consistent with the proposed mechanism when, for example, electron-rich aniline 4 reacts with a, 3-unsaturated aldehyde 5 to give quinoline 6. ... 

Bischler has suggested that anilines undergo 1,4-addition followed by dehydration which would explain the inherent regioselectivity. Mechanistic studies suggest that the reaction involves the reversible formation of diazetidinium ions 7 and there irreversible cyclization to quinolines. ... 

Because of the extremely low solubility of the cyclized products, only the 8-acetyl-9-X oxo-6,9-dihydrothiazolo[5,4-g]quinoline was isolated. On the other hand, 6-substituted derivatives having the same possibility to produce linearly or angularly annelated thiazoloquinolines cyclize regioselectively. 

Methylbenzotriazole derivatives with an aminoethylene substituent in position 4 also regioselectively produce only the angularly annelated 7-ethoxycarbonyl-6-0X0-6,9-dihydro-2-methyl-2//-triazolo[4,5-/i]quinoline 158. Under alkaline hydrolysis the ester 158 yielded the corresponding acid 159 (90CCC1038, 92FA1001). 

Strong effects of the catalyst on the regioselectivity have been observed in the cycloadditions of a variety of heterocyclic dienophiles. Some results of the BF3-catalyzed reactions of quinoline-5,8-dione (21) and isoquinoline-5,8-dione (22) with isoprene (2) and (E)-piperylene (3) [25], and of the cycloadditions of 4-quinolones (23a, 23b) as well as 4-benzothiopyranone (23c) with 2-piperidino-butadienes, are reported [26] in Scheme 3.8 and Equation 3.2. The most marked... 

Grignon-Dubois and coworkers have shown that reduction of a quinoline using zinc and acetic acid in THF gives the dimeric compound 3-177 via intermediate 3-176 (Scheme 3.47) [70J. Usually, a mixture of the syn- and anti-products is formed the substituent has some influence on the regioselectivity of the dimerization and cydization step. With R = H and R = 6-Me, only the benzazepine 3-177 were produced, by a head-to-head dimerization. 

Related alkyne couplings yield tricyclic quinolines via a regioselective amination/C-H functionalization pathway (Equations (104) and (105)).98... 

Regioselective cyclization of /V-(4-benzoyl-5-benzimidazolyl)amino-methylenemalonates (969, R = H, Me) was observed. When the cyclization was carried out in polyphosphoric acid, then 4-phenylimidazo-[4,5-/]quinoline-5-carboxylates (970) were obtained, while the thermal cyclization in diphenyl ether at 200°C, or the cyclization in a mixture of phosphoryl chloride and polyphosphoric acid afforded 4-benzoyl-8-hydroxyimidazo[5,4-g]quinoline-7-carboxylates (971) (89KFZ692). 

Halogenated quinolines very often nndergo nncleophilic addition with BuLi, so must be lithiated with LDA or LiTMP " The regioselectivity of their reactions parallels that of the pyridines, and similar halogen migrations are observed (Scheme 116) . ... 

Quiroga J, Mejia D, Insuasty B et al (2001) Regioselective synthesis of 4, 7, 8, 9-tetrahydro-2H-pyrazolo[3, 4-b]-quinolin-5(6H)-ones. Mechanism and structural analysis. Tetrahedron 57(32) 6947-6953... 

Bennasar et al. reported a new radical-based route for the synthesis of calothrixin B (378) (869). This synthesis starts from the 2,3-disubstituted N-Boc indole 1558 and uses a regioselective intramolecular acylation of a quinoline ring as the key step for the construction of the calothrixin pentacyclic framework. Chemoselective reaction of in s/fM-generated 3-lithio-2-bromoquinoline [from 2-bromoquinoline 1559 with LDA] with the 3-formylindole 1558 followed by triethylsilane reduction of the... 

Quinoline and isoquinoline react in an analogous manner with benzene in conjugated superacids (HCI-AICI3, HBr-AlBr3) to yield predominantly cis-5,1-diphenyl-5,6,7,8-tetrahydroquinoline and <7,v-6,8-diphenyl-5,6,7,8-tetrahydroisoqui-noline, respectively (75-94% yield).297 The regioselectivity observed corresponds to the most stable dicationic intermediates 73 and 74. Unsaturated imides298 exhibit similar behavior in triflic acid (Scheme 5.33). 

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