Stereoselective Synthesis of Hexahydro‑1<i>H</i>‑pyrano- and thiopyrano[3,4‑<i>c</i>]quinoline Derivatives through a Prins Cascade Cyclization

A cascade reaction of (E)-5-(arylamino)­pent-3-en-1-ols and thiols with various aldehydes in the presence of 30 mol % BF3·OEt2 in 1,2-dichloroethane at 80 °C affords a novel class of trans-fused hexahydro-1H-pyrano­[3,4-c]­quinolines and hexahydro-1H-thiopyrano­[3,4-c]­quinolines in good to excellent yields with high selectivity. The condensation of (Z)-5-(arylamino)­pent-3-en-1-ol with aldehydes provides the corresponding cis-fused products under similar conditions.