Carbon‐nitrogen bond formation in cyclisation by deoxygenation, thermolysis or photolysis of phenylimidazo[1,2‐a][1,8]naphthyridines

Triethyl phosphite deoxygenation of 2‐(2‐nitrophenyl)imidazo[1,2‐a][1,8]naphthyridine (3) led to the C‐insertion to give the indoloimidazonaphthyridine 5. Our attempt to promote the N‐insertion by blocking the C‐3 position failed. Triethyl phosphite deoxygenation of 1‐nitroso‐2‐(4‐fluorophenyl)imidazo[1,2‐a][1,8]‐naphthyridine (12) led to the corresponding amine structure (15). Thermolysis and photolysis of 6,8‐dimethyl‐2‐(2‐azidophenyl)imidazo[1,2‐a][1,8]naphthyridine (17) are also reported.