1.2- Dihydroquinolines disproportionation reaction

No 3,4-dihydroquinolmes of type 29 have ever been isolated, or even detected by any spectroscopic method however, their intermediacy was postulated for the disproportionation reaction of 1,2-dihydroquinolines (85CJC412) and for flash-vacuum thermolysis of triazoles (98JOC5779). 

During the study of this substitution reaction of oximes, we examined the cyclization of 2-(3-hydroxyphenyl)ethyl ketone 0-2,4-dini-trophenyl oxime 80a. When 80a was treated with NaH, quinoline 82a and 1,2,3,4-tetrahydroquinoline 83a, which are the disproportionation products of the initially formed 3,4-dihydroquinoline 81, were obtained in good yield. Both E- and Z-isomers cyclized to give the 8-hydroxyquinolines 82a and 83a, with almost the same reaction rate (Scheme 35). ... 

Lithium in liquid ammonia conditions can produce l,4-dihydroquinoline" and 3,4-dihydroisoquinoline." Conversely, lithium aluminium hydride reduces generating l,2-dihydroquinoline" and 1,2-dihydroisoquinoline. These dihydro-heterocycles can be easily oxidised back to the fully aromatic systems, or disproportionate, especially in acid solution, to give a mixture of tetrahydro and re-aromatised compounds. Stable dihydro-derivatives (see also 9.13) can be obtained by trapping following reduction, as a urethane, by reaction with a chloroformate. Quaternary salts of quinoline and isoquinoline are particularly easily reduced, either catalyticaUy or with a borohydride in protic solution, giving... 

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See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ , ]

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