Tandem five membered-ring selective Prins reaction and Friedel-Crafts reaction

A tandem reaction consisting of five membered-ring selective Prins cyclization and subsequent Friedel-Crafts cyclization was developed. The reactions of phenyl homoallylic alcohol 3 and benzaldehyde derivatives 6 afforded tetrahydroindenofurans 7 or pentacyclic products 8, depending upon the quantity of 6. Also homoallylic alcohol 12 having an alkyne-cobalt moiety reacted with 6 to give rise to tetrahydroindenofurans 13 in good yields.