The Prins Cascade Cyclization Reaction for the Synthesis of Angularly‐Fused Tetrahydropyran and Piperidine Derivatives

2-Arylethylbut-3-en-1-ol is found to undergo smooth Prins cascade reactions with various aldehydes in the presence of Sc(OTf)3 (10 mol-%) and a stoichiometric amount of TsOH to afford the corresponding trans-fused hexahydro-1H-benzo[f]isochromenes in good yields with excellent selectivity. Likewise, N-tosyl-2-phenethylbut-3-en-1-amine gives trans-fused octahydrobenzo[f]isoquinoline derivatives under similar conditions. This is the first example of the synthesis of hexahydro-1H-benzo[f]isochromene and octahydrobenzo-[f]isoquinoline from 2-arylethylbut-3-en-1-ol and N-tosyl-2-phenethylbut-3-en-1-amine, respectively.