Syntheses of Polycyclic Tetrahydrofurans by Cascade Reactions Consisting of Five-Membered Ring Selective Prins Cyclization and Friedel–Crafts Cyclization

A novel cascade reaction
consisting of a five-membered ring selective
Prins cyclization and a subsequent Friedel–Crafts cyclization
is reported. Treatment of homocinnamyl alcohols and aromatic aldehydes
with BF3·OEt2 in CH2Cl2 afforded hydrocyclopentafurans. Also hydrocyclopentafurans underwent
the same cascade reaction after its furan ring cleavage upon treatment
with BF3·OEt2 at room temperature. Various
combinations of hydropentafurans and aromatic aldehydes or indole
aldehydes permitted divergent synthesis of diquinane-furans stuck
in aromatic rings.