Benzopyrones. Part 23. Cyclization of o-amino carboxamides and related compounds

Abstract

Cyclization of 2-amino-6-bromo-4-oxochromene-3-carboxamide (5) with diethyl oxalate–sodium ethoxide gave the benzopyrano[2,3-d]pyrimidine-4,6-dione (6). Ethyl 3-amino-2-carbamoyl-4-oxo-chromene-6-carboxylate (10a) in a similar reaction gave derivatives of a novel ring system benzopyrano[3,2-d]pyrimidine (8) but when 3-amino-4-oxochromene-2-carboxamide (10b) was subjected to the same reaction, the novel ring system benzopyrano[3,2-e]-1,4-diazepine (14a) was obtained in high yield. This structure, which contains the hitherto unknown 1,4-diazepine-2,3,5-trione ring, is supported by spectroscopic and chemical evidence. The presence of a 3-amino and a 2-carbonyl group in a chromone has an unexpected shielding effect on the chemical shift of C-8. The course of the cyclization was studied. Attempts to cyclize 3-aminomethyl-4-oxochromene-2-carboxamide (28; X = Y = H), a homologue of (10b), failed but a new ring system (31) was obtained when ethyl 3-bromo-4-oxochromene-2-carboxylate (29; R¹= OEt) reacted with o-phenylenediamine.