By the Meissenheimer Reaction on 1,5-Naphthyridine -Oxides

The conversions of 1,5-naphthyridine A-oxides into C-halogeno-l,5-naphthyr-idines by the Meissenheimer reaction (POCl3 or POBr3) or a related reaction (Br2 in Ac20) both suffer from the fact that two or more products are usually formed in each case. This introduces a sometimes difficult separation procedure, so that such 

Similar treatment of 1,5-naphthyridine 1,5-dioxide (31) has been reported to give only 2,6-dichloro-1,5-naphthyridine (33) (POCl3, reflux, 20 min 37 or 54%)971,1047 or a mixture of 2,4- (32), 2,6- (33), 2,7- (34), 2,8- (35), and 3,8-dichloro-1,5-naphthyridine (36) from which all except the 2,7-isomer were isolate eventually in a pure state.233 

Treatment of 1,5-naphthyridine 1-oxide with bromine in acetic anhydride gave a complicated mixture in which 2-bromo- and 2,7-dibromo-1,5-naphthyridine, 3-bromo- and 3,6-dibromo-1,5-naphthyridine 1-oxide, and 3-bromo-l, 5-naphthyridin-2 (l//)-one were identified.317 

---