Lewis Acidic Chloroaluminate Ionic Liquids: Novel Reaction Media for the Synthesis of 4-Chloropyrans

1‐n‐Butyl‐3‐methylimidazolium chloroaluminate [bmim]Cl·AlCl3 (N = 0.56−0.67) ionic liquid has been employed as an alternative reaction medium to conventional acid catalysts for Prins cyclizations, to produce 4‐chlorotetrahydropyran derivatives in excellent yields and in short reaction times. The ionic liquid plays a dual role as both catalyst and solvent, providing a rapid and efficient route to the synthesis of chlorotetrahydropyrans. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)