Annulative π‑Extension (APEX) of Heteroarenes with Dibenzosiloles and Dibenzogermoles by Palladium/o‑Chloranil Catalysis

Annulative π-extension (APEX) reactions of heteroarenes are described herein. A catalytic system comprising a cationic palladium species and o-chloranil using dimethyldibenzosiloles as π-extending agents enabled the extension of the π-system of benzo­[b]­thiophenes. π-Extended dibenzofurans and carbazoles could also be obtained from benzofuran and N-tosylindole, respectively, with dimethyldibenzogermole as a germanium-based π-extending agent. Mechanistic investigations indicated two possible reaction pathways involving carbopalladation-based double C–H arylation of benzothiophene or formal cycloaddition/oxidation cascades.