Copper-Catalyzed One-Pot Cross-Dehydrogenative Thienannulation: Chemoselective Access to Naphtho[2,1‑b]thiophene-4,5-diones and Subsequent Transformation to Benzo[a]thieno[3,2‑c]phenazines

A facile, cost-effective, and highly efficient copper-catalyzed, TEMPO-mediated straightforward synthesis of 2,3-disubstituted naphtho­[2,1-b]­thiophene-4,5-diones has been achieved via cross-dehydrogenative thienannulation. The reaction proceeded via in situ generated naphthalene-1,2-diones by dearomatization of β-naphthols, followed by oxidative heteroannulation with α-enolic dithioesters chemoselectively in an open flask. Further, the naphtho­[2,1-b]­thiophene-4,5-diones undergo l-proline-catalyzed cross-dehydrative coupling with ortho-phenylenediamine enabling pentacyclic benzo­[a]­thieno­[3,2-c]­phenazines in good yields under solvent-free conditions. A mechanistic rationale for this cascade reaction sequence is well supported by the control experiments.