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. 2‐Arylethylbut‐3‐en‐1‐ol undergoes a Prins cascade reaction with aldehydes to afford 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.