Functionalized Contorted Polycyclic Aromatic Hydrocarbons by a One-Step Cyclopentannulation and Regioselective Triflyloxylation

The oxidative cyclodehydrogenation (often named the Scholl reaction) is still a powerful synthetic tool to construct even larger polycyclic aromatic hydrocarbons (PAHs) by multiple biaryl bond formations without the necessity of prior installation of reacting functional groups. Scholl-type reactions are usually very selective although the resulting products bear sometimes some surprises, such as the formation of five-membered instead of six-membered rings or the unexpected migration of aryl moieties. There are a few examples, where chlorinated byproducts were found when FeCl3 was used as reagent. To our knowledge, the direct functionalization of PAHs during Scholl-type cyclization by triflyloxylation has not been observed. Herein we describe the synthesis of functionalized PAHs by the formation of five-membered rings and a regioselective triflyloxylation in one step. The triflyloxylated PAHs can be used as reactants for further transformation to even larger contorted PAHs.