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Rh/Ag-Mediated Peri-Selective Heteroarylation/Single Electron Transfer Annulation Cascade of 1‑(Methylthio)naphthalenes and Analogues: Road Less Traveled to Benzo[de]thioacenes

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posted on 31.05.2019, 00:00 by Shiping Yang, Rui Cheng, Min Zhang, Zhengyang Bin, Jingsong You
Reported herein is a one-shot synthesis of benzo­[de]­thioacenes via a Rh-catalyzed peri-selective heteroarylation/Ag-mediated SET intramolecular cyclization sequence of 1-(methylthio)­naphthalenes and heteroatom-embedded analogues in HFIP. Moreover, the different alcohols enable an exquisite switch in the reaction process. t-BuOH instead of HFIP delivers biaryl sulfides rather than cyclized products. By separation of rhodacycle species, control experiments, EPR experiments, and especially capture and isolation of thiophene radical adduct with BHT, the mechanistic pathway has been illustrated clearly. The formation of a sulfur-bridged six-membered ring via SET cyclization of the cation-radical to the methylthio group presented herein is intrinsically different from the conventional acid-mediated cyclization of sulfoxides. The annulative π-extension developed herein exemplifies the high compatibility of oxidative C–H activation and radical chemistry.