Tellurium in organic synthesis: X. Synthesis of 3-halogenobenzo [b] tellurophene derivatives

Several substituted 3-halogenobenzob] tellurophenes have been synthesized by treating phenylacetylenes with TeO₂ in acetic acid in the presence of a lithium halide. A mechanism is postulated involving an electrophilic attack by a solubilized tellurium species on the acetylenic bond with introduction of a halogen atom followed by cyclization to the benzob]tellurophene system. The benzob]tellurophenes can be easily chlorinated with Cl₂ gas to yield benzob]tellurophene 1,1-dichloride derivatives, but attempted lithiation is the 3-position was unsuccessful and resulted in a ring rupture. When refluxed in trifluoroacetic acid 3-chlorobenzob]tellurophene was converted into 3-oxo-2,3-dihydrobenzob]tellurophene.