Studies on tellurium-containing heterocycles. Part 22. Tellurazepine ring system: preparation of 1,5-benzotellurazepin-4-ones and their conversion into fully unsaturated 1,5-benzotellurazepines

The treatment of o-iodopropiolanilides (12), which were easily prepared from o-iodophenylisocyanate (11) and ethynylmagnesium bromide, with sodium hydrogen telluride resulted in the intramolecular ring closure of the presumed phenyltellurol intermediates (13) to a triple bond to give the 1,5-benzotellurazepin-4-ones (14) as the sole characterized products. The obtained amides (14) were easily converted into fully unsaturated lactim 4-methoxy-1,5-benzotellurazepines (18) by treatment with trimethyloxonium tetrafluoroborate. Decomposition by thermolysis of the 4-methoxyazepinenes (18) afforded the 4-methoxyquinolines (19) with extrusion of a tellurium atom.