Synthesis of acenaphthylene-fused heteroarenes and polyoxygenated benzo[<i>j</i>]fluoranthenes via a Pd-catalyzed Suzuki–Miyaura/C–H arylation cascade

Acenaphthylene-fused heteroarenes with a variety of five- and six-membered heterocycles such as thiophene, furan, benzofuran, pyrazole, pyridine and pyrimidine were synthesized via an efficient Pd-catalyzed reaction cascade in good to high yields (45-90%). This cascade involves an initial Suzuki-Miyaura cross-coupling reaction between 1,8-dihalonaphthalenes and heteroarylboronic acids or esters, followed by an intramolecular C-H arylation under the same conditions to yield the final heterocyclic fluoranthene analogues. The method was further employed to access polyoxygenated benzo[<i>j</i>]fluoranthenes, which are all structurally relevant to benzo[<i>j</i>]fluoranthene-based fungal natural products. The effectiveness of our strategy was demonstrated via a concise, four-step synthesis of the tetramethoxybenzo[<i>j</i>]fluoranthene derivative <b>18</b>, which represents a formal total synthesis of the fungal natural product bulgarein.