9,10-Phenanthrenequinone (PQ) reacts with ketones under FeCl3 catalysis to furnish a variety of structurally diverse furan annulated products. While the reaction of PQ with acetone and cyclopentanone furnishes furan annulated ketals, its reaction with ethyl alkyl ketones provides 3-furaldehyde annulated products. In contrast to the reaction of PQ with cyclopentanone, its reaction with cyclohexanone furnishes a tetrahydrobenzofuran annulated secondary alcohol. The reactions of PQ with cycloheptanone and cyclooctanone take a different course to provide 7,8-dihydro-6H-cyclohepta[b]furan and 6,7,8,9-tetrahydrocycloocta[b]furan annulated products, respectively. Mechanistically, the above reactions go through aldol condensation, dehydration and cyclization to form furan-phenanthrene annulated products where in each step FeCl3 catalysis is involved.
