Quinolines ring formation

In an extension of quinoline ring formation by reaction of enolate anions with o-trifluoromethylaniline, the enolate anion was replaced with anion of nitrile (44) to give quinoline (45) (Scheme 19) <94TL(35)7597). 

Preparation o the key intermediate for the chloroquinoline series starts with Shiff base formation of metachloroaniline with ethyl oxaloacetate (66). Heating of the intermediate leads to cyclization into the aromatic ring and consequent formation of the quinoline ring (67). Saponification of the ester to the acid... 

Pyridylcarbonyl)- and 2-(2-quinolylcarbonyl)benzoic acids possess the open-chain structure in the solid state (84KGS1231). In dioxane solution, the ring-chain equilibrium is observed. Protonation of the pyridine or quinoline ring nitrogen atom leads to the formation of the protonated cyclic forms 11. Evidently, protonation stabilizes the tautomer that is the stronger base, i.e., the cyclic form. 

Polyquinolines (PQ) are obtained by the Friedlander reaction of a bis-o-aminoaromatic aldehyde (or ketone) with an aromatic hisketomethylene reactant [Concilio et al., 2001 Stille, 1981]. The quinoline ring is formed hy a combination of an aldol condensation and imine formation (Eq. 2-221). Polymerization is carried out at 135°C in m-cresol with poly (phosphoric acid) as the catalyst. The reaction also proceeds under base catalysis, but there... 

In a manifestation of the reaction shown above, quinoline rings have also been formed by the cycloaddition of /V-arylketenimines 543 with 3,4-dihydro-2//-pyran 455 under high-pressure conditions (Scheme 100) <2001H(55)1971>. The reaction is proposed to proceed via the initial formation of 544 by attack of the enol ether on the protonated ketenimine subsequent electrophilic aromatic substitution gives 545. Protonation of the enamine to give 546 is followed by elimination to produce 547. Protection of the alcohol with 455 gives 548. 

Formation of pentacycle 55 was consistent with the radical addition-quinoline rearomatization-overoxidation sequence depicted below. Thus, the initially formed acyl radical L undergoes regioselective cyclization upon the 4-position of the quinoline ring to give the azacyclohexadienyl radical M, which is probably oxidized by hydrogen abstraction at the hands of the initiator AIBN <04AGE95>. A new hydrogen abstraction at the doubly... 

Combes quinoline synthesis. Formation of quinolines by condensation of (i-di ketones with primary arylamines followed by acid-catalyzed ring closure of the intermediate Schiff base. 

The X-ray-determined structure of the complex of 16 and 19 with quaternary salt 15 revealed that the primary discriminative forces leading to an efficient resolution are the formation of directional hydrogen bonds of hydroxy groups of cinchonidine and BINOL with the halide anion as well as aryl-aryl interaction between the naphthyl and the quinoline rings [40]. 

CycUzations. Activation of an allenyl group with SnCLt and linkage to a C-nucleophile constitute a ring formation process. The reaction of Al-arylaldimines with allylsilanes (or allylgermanes) in the presence of SnCl, leads to 2,4-disubstimted 1,2,3,4-tetrahydro-quinolines due to rapid interception of the carbocationic intermediates. 

The biosynthetic pathway to furoquinoline alkaloids apparently involves formation of the quinoline ring before introduction of the side chains, for... 

Shamma s synthesis (Scheme 29) leaves the formation of the quinoline ring to a late stage, building up a tricyclic pyridone-ketone (121) which is then subjected to a Friedlander quinoline ring synthesis. 

---