Brønsted Acid-Catalyzed Tandem Double Friedel–Crafts Alkylation to Construct a Dihydrophenalene Skeleton Bearing an All-Carbon Quaternary Center

An efficient Brønsted acid-catalyzed tandem reaction has been developed for the construction of a dihydrophenalene skeleton bearing an all-carbon quaternary center. Starting with 2-naphthol-tethered ketones and indoles, the tandem reaction catalyzed by TsOH monohydrate proceeded smoothly with good to excellent efficiency through a double Friedel–Crafts alkylation process. Moreover, the synthetic utility of this method was demonstrated by easy gram-scale preparation and product transformations to fused hexacyclic compounds.