1.2.3- Triazino quinolines

Eight isomeric structures can be drawn for the 1,2,4-triazino-quinolines, which have fusion only on the heterocyclic ring. Fusion could also exist on the benzo ring. Only six isomers were reported during the period of this review. 

In a similar way, 3-amino-1,2,4-triazino[6,5-c]quinoline 4-oxides 127 were synthesized by the reaction of 4-chloro-3-nitroquinoline 128 with guanidine, followed by the cyclization of intermediate arylguanidines under basic conditions (81JHC1537). 

Nitroquinoline (138) undergoes direct cyclocondensation with aromatic hydra-zones 139 in the presence of sodium hydride in DMF to give low yields of the corresponding [l,2,4]triazino[6,5-fc]quinolines 140 and pyrazolo[3,4-/] quinolines... 

Triazinoindole 146 was obtained (74T3997) in a mixture with quinoline 148 on thermolysis or of 3-(alkylthio)-6,7-dihydro[l,2,4]triazino[l,6-c]quinazolin-5-ium-l-olate 144 acid hydrolysis. The reaction presumably took place via the decomposition of 144 to a ketone and 142, which then cyclized. Compound 144 was prepared by the condensation of 142 with aldehydes, ketones, or their equivalents. Reaction of 142 with 3-amino propanol gave 143, which cyclized to 145 and then to 147 with base [80ACH(104)107] (Scheme 32). 

Treatment of 8-fluoro-4-hydroxy-l/7-[l,2,4]triazino[4,5- ]quinoline-l,6(2/7)-dione 72 with POCl3 readily and selectively gave compound 103 which was subsequently hydrodechlorinated affording 104 (Scheme 6) <2003JHC789>. 

Nitroquinoline 209 enters into a direct cyclocondensation with aromatic hydra-zones in NaOH/DMF giving pyrazolo[3,4-/]quinolines 210 and (or) triazino[6,5-/ quinolines 211 in low to moderate yield (Scheme 62) (OOOL413). Their ratio mainly depends on the structure of the starting hydrazone. For example, electron-donating substituents in its aryl moiety assist triazine ring closure. Evidently, pyrazoles 210 are products of two consecutive SNH and SN ipso reactions, whereas conversion of 209 into 211 looks rather complicated and better corresponds with cascade hetero-cyclizations considered in Section III.D.l. 

Chloro-l,2,4-triazino[5,6-c]quinoline (186) was obtained by treatment of the triazin-3-one (187) with POCl3 <74JMC244>. 

A series of l,2,4-triazino[5,6-c]quinolines have been prepared via a common route. Thus, 4-[fi-(ethoxymethylene)hydrazino]-3-nitroquinoline (244), prepared from 4-hydrazino-3-nitroquinoline (243) by reaction with triethyl orthoformate, was hydrogenated in ethanol over a palladium catalyst to give the dihydro compound (184) (96%). Dehydrogenation yielded the desired compound (185) (90%) (Scheme 19) <73GEP(0)2322394>. 

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