Chemodivergent Reactions of Aromatic Ring-Annulated Hexahydrocyclopentafurans with Various Aldehydes

Hexahydro-2H-cyclopenta[b]furan fused to electron-rich aromatic rings reacts with various aromatic aldehydes in different modes to build diverse frameworks. The reaction of a dimethoxybenzene-fused cyclopentafuran generated diquinanes fused with a hydrofuran ring, indenopyrans, or diarylindanes depending upon the type of aromatic aldehydes, whereas an indole-annulated cyclopentafuran generated another type of diquinane fused with hydrofuran ring or benzylidenecyclopentafuran. The chemodivergence is due to the different properties between indole- and dimethoxybenzene-fused hydrocyclopentafurans. Namely, Lewis acid-promoted furan-ring opening of the substrates resulted in the formation of an electrophilic or a nucleophilic intermediate, respectively. Additionally, the observed chemodivergence can be attributed to the distinctive electronic properties of three classified aromatic aldehydes. Of particular interest is that 2,4-dimethoxybenzaldehyde reacted with the dimethoxybenzene-fused cyclopentafuran at the benzene ring, whereas it reacted with the indole-fused cyclopentafuran at the formyl group.