Some transformations of 3‐amino‐4‐alkoxycarbonyl‐6‐hydroxy‐2 H ‐1‐benzopyran‐2‐ones. The synthesis of [1] benzopyrano[3,4‐ d ]‐[1,3]oxazine and [1] benzopyrano[3,4‐ d ]pyrimidine derivatives

Acylation of 4‐alkoxycarbonyl‐3‐amino‐6‐hydroxy‐2 H ‐1‐benzopyran‐2‐one derivatives 3 and 4 gave under mild conditions the O ‐substituted derivatives 5–10, N,O ‐disubstituted derivative 11 and N,N ‐disubstituted derivative 12 . The compound 4 was transformed with benzoyl chloride under more drastic conditions into 13 , a derivative of a new heterocyclic system 2‐benzopyrano[3,4‐ d ][1,3]oxazine. The derivatives of 1‐benzopyrano‐[3,4‐ d ]pyrimidine 19 and 20 were prepared either from 3 and 4 through the corresponding N ‐heteroarylformamidines 14 and 15 and N ‐heteroarylformamide oximes 17 and 18 or by cyclization of thiourea derivative 20 .