Stereoselective Synthesis of Hexahydro-1H-pyrano- and thiopyrano[3,4-c]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.