Brønsted Acid-Mediated Stereoselective Cascade Construction of Functionalized Tetrahydropyrans from 2-(Arylmethylene)cyclopropylcarbinols and Aldehydes

(<i>E</i>)- and (<i>Z</i>)-2-(Arylmethylene)cyclopropylcarbinols <b>1</b> could be converted to the corresponding tetrahydropyrans <b>2</b> and <b>3</b> stereoselectively in the presence of Brønsted acids MsOH or TsOH under mild conditions. A plausible Prins-type reaction mechanism has been proposed.