Dehalogenation of Halogeno-1,6-Naphthyridines

5-Chloro-7-methyl-l,6-naphthyridine (43) underwent direct hydrogenolysis to give 7-methyl-1,2,3,4-tetrahydro-l,6-naphthyridine (44) (Pd/CaC03, MeOH, H2, 20°C %), but the same substrate (43) gave 4-hydrazino-7-methyl-l, 6-naphthyridine (45) (H2NNH2.H20, MeOH, reflux, 10 min 95%) and thence 7-methyl-l,6-naphthyridine (46) (AcOH, H20, CuS04, reflux, 10 min 65%).1285 

Ethyl 1 -(2-chloroethyl)-7-(4-methylpiperazin-1 -yl)-4-oxo-1,4-dihydro-1,6-naphthyridine-3-carboxylate (48, Q = CH2CH2C1, R = Et) gave 7-(4-methyl- 

A few rarely used reactions of halogeno-l,6-naphthyridines are exemplified 

Note It is quite remarkable that very few deliberate hydrolyses of these halogenonaphthyridines have been reported. 3-(3,5-Dimethyoxyphenyl)-2,7-difluoro-l,6-naphthyridine gave 3-(3,5-dimethox-yphenyl)-7-fluoro-l,6-naphthyridin-2(l//)-one (49) (NaOH, H20, THF, 53°C, 3 days 95%).564 

2-Chloro-5-dichloromethyl-l,6-naphthyridine gave 5-dichloromethyl-l, 6-naphthyr-idin-2(l//)-one (50) (6M HC1, 95°C, 90 min 67%).490 

---