4-Chloro-8-nitro-1.6-naphthyridine, reduction chloride

Subjecting 8-chloro-5-iiitro-l,7-iiaphthyridiiie (97) to reduction with tin(II) chloride leads, besides loss of the chloro atom and reduction of the nitro group, i.e., formation of 5-amino-l,7-naphthyridine (131, 22%), to the formation of small amounts of 5-amino-6,8-dichloro- (132, 1.5%) and 5-amino-6-(or 8-)chloro-l,7-naphthyridine (133, 2.5%) (88PJC305). 

Catalytic hydrogenation (Pd/C) of 2-chloro-3-nitro-l,5-naphthyridine (125, R = Cl) in methanolic solution afforded 3-amino-l,5-naphthyridine (126, R = H, 74%) isolated in the form of its trihydrochloride (40MI1). Similar Pd/C hydrogenation of 2-ethoxy-3-nitro-l,5-naphthyridine (125, R = OEt) gave 3-amino-2-ethoxy-l,5-naphthyridine (126, R = OEt, 47%) (80RTC83). Reduction with tin(II) chloride in hydrochloric acid also leads to 126, (R = OEt, 73%) (63RTC997). 

Tin(II) chloride reduction of both 4-chloro-3-nitro-l,8-naphthyridine (129, R = Cl) (79PJC1665) and 3-nitro-l,8-naphthyridine (129, R = H) (76S691) gave in 30-35% yield 3-amino-l,8-naphthyridine (130, R = H) reduction of the 4-amino-3-nitro compound (129, R = NH2) yielded 3,4-diamino-l,8-naphthyridine (130, R = NH2,37%) (79PJC1665). 

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