Modulating Prins Cyclization versus Tandem Prins Processes for the Synthesis of Hexahydro‐1H‐pyrano[3,4‐c]chromenes

Abstract We propose the synthesis of biologically relevant hexahydro‐1 H ‐pyrano[3,4‐ c ]chromenes, via a tandem Prins/Friedels‐Crafts process, catalyzed by BF 3 .Et 2 O, starting from ( E )‐ and ( Z )‐5‐phenoxypent‐3‐en‐1‐ol. The diastereoselectivity of the process is controlled by the geometry of the homoallylic alcohol. We also point out that the Prins product can be obtained in high yields and good diastereoselectivity when the reaction is promoted by AlCl 3 as Lewis acid in the presence of an external nucleophile.