Organic azides in heterocyclic synthesis, 12. Thermal cyclization of 4‐azido‐3‐formyl‐2‐quinolones to isoxazolo[4,3‐c]quinolones

Abstract
Thermolysis of the 4‐azido‐3‐formyl‐2‐quinolone 6, which was prepared from the 4‐hydroxy‐2‐quinolone 1, afforded the ringclosed isoxazoloquinolone 7. 3‐(Arylaminomethylene)‐2,4‐quinolinediones 2 could not be transformed into an azide precursor in order to obtain the corresponding pyrazoloquinolone but yielded by attempted chlorination either 5‐methyldibenzo[b,h][1,6]naphthyridine‐6(5H)‐one (9) or 4‐chloro‐3‐formyl‐1‐methyl‐2(1H)‐quinolone (5).

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