Synthesis and reactions of 2 H ‐Benzothieno[3,2‐ d ][1,3]oxazine‐2,4(1 H )‐dione

The title compound 5 is synthesized by the reaction of the potassium salt of 3‐aminobenzo[ b ]thiophene‐2‐carboxylic acid with phosgene. Compound 5 is readily alkylated to give 6 with methyl iodide, benzyl bromide, or propargyl bromide in the presence of sodium hydride. Reaction of 5 and 6 with nucleophiles follows specifically different pathways. Compound 5 is readily ionized to the isocycanate species 13 and subsequently reacts with methanol or methylamine to produce exclusively the carbamate 7 or ureido acid 9 . The N ‐substituted derivative 6 , in analogous reactions with methanol or methylamine, produce exclusively the amino ester 8 or the amino amide 10 . The N‐benzyl derivative 6b reacts with the cyclic S ‐methylthiopseudourea 11 to give the tetracycle 12 , a new ring system.