Synthesis of 1,3-benzotellurazole derivatives from phenyl ureas and tellurium tetrachloride

A method has been developed to prepare previously inaccessible substituted 1,3-benzotellurazoles following an efficient two-step process, consisting of the tellurination of electron rich phenyl ureas with tellurium tetrachloride and subsequent ring closure of the resulting aryl tellurium trichlorides. Tellurination occurs regiospecifically ortho to the urea moiety due to intramolecular Te–O coordination, producing highly crystalline solids that are readily isolated in yields up to 83 %. Subsequent ring closure, accomplished by heating with phosphorus trichloride and subsequent reduction with hydrazine hydrate, provides access to 1,3-benzotellurazole derivatives. Selected products were characterized by X-ray crystallography.