Unexpected Heteroannulation and Chlorination of Benzothiadiazine Derivatives Mediated by DDQ

In the course of studies directed toward the synthesis of new tubulin polymerization inhibitors, several benzothiadiazine derivatives were prepared. The oxidative dehydrogenation reaction with DDQ unexpectedly led to heteroannulation and chlorination of the benzothiadiazine tricycles. A rationale for their formation is proposed.