Studies on synthesis of coumarin derivatives. XV. On the preparation of ethyl pyranobenzoxazole-carboxylates.

Abstract

The reaction between ethyl ο-nitro-hydroxy-3-coumarincarboxylates (I, VI, and XI) with zinc powder in acetic acid, acetic anhydride, or a mixture of acetic acid and acetic anhydride were examined. The reaction of the ο-nitro-hydroxy compounds in acetic acid gave ethyl ο-amino-hydroxy-3-coumarincarboxylates (II, VII, and XII) and in a mixture of acetic acid and acetic anhydride yielded ethyl ο-acetamido-hydroxy-3-coumarincarboxylates (III, VIII, and XIII). The amino and acetamido compounds were refluxed with acetic anhydride to obtain ethyl ο-dicaetylamino-acetoxy-3-coumarincarboxylate (IV, IX, and XIV). The acetamido compounds obtained were fused with phosphorous pentoxide to yield new ethyl pyranobenzoxazolecarboxylates (V, X, and XV).