Short Synthesis of Sulfur Analogues of Polyaromatic Hydrocarbons through Three Palladium-Catalyzed C–H Bond Arylations

An expeditious synthesis of a wide range of phenanthro­[9,10-b]­thiophene derivatives, which are a class of polyaromatic hydrocarbon (PAH) containing a sulfur atom, is reported. The synthetic scheme involves only two operations from commercially available thiophenes, 2-bromobenzenesulfonyl chlorides and aryl bromides. In the first step, palladium-catalyzed desulfitative arylation using 2-bromobenzenesulfonyl chlorides allows the synthesis of thiophene derivatives, which are substituted at the C4 position by an aryl group containing an ortho-bromo substituent. Then, a palladium-catalyzed one-pot cascade intermolecular C5-arylation of thiophene using aryl bromides followed by intramolecular arylation led to the corresponding phenanthro­[9,10-b]­thiophenes in a single operation. In addition, PAHs containing two or three sulfur atoms, as well as both sulfur and nitrogen atoms, were also designed by this strategy.