Synthesis of a New Tricyclic Compound, 5H-2-Methoxycarbonyl-4-oxofuro[2, 3-b][1, 5]benzothiazepine

Methyl 5-(2-carboxyphenylthio)-2-furancarboxylate (2) was obtained by the nucleophilic substitution of methyl 5-nitro-2-furancarboxylate (3) with the disodium salt of thiosalicylic acid, and chlorination of 2 gave methyl 5-(2-chloroformylphenylthio)-2-furancarboxylate (4). The reaction of 4 with sodium azide gave methyl 5-(2-azidocarbonylphenylthio)-2-furancarboxylate (8) and methyl 5-(2-isocyanatophenylthio)-2-furancarboxylate (9) was obtained by the thermolysis of 8. Finally, the new tricyclic compound, 5H-2-methoxycarbonyl-4-oxofuro[2, 3-b][1, 5]benzothiazepine (1) was obtained by cyclization of 9 in the presence of aluminum chloride.