High Regioselective Diels---Alder Reaction of Myrcene with Acrolein Catalyzed by Zinc-Containing Ionic Liquids

Abstract: The ambient zinc-containing ionic liquids, MX-ZnCl2, functioning as both Lewis acid catalyst and green solvent, are employed for a high regiose-lective Diels–Alder reaction of myrcene with acro-lein for the first time, where MX is either 1-butyl-3-methylimidazolium chloride (BmimCl), 1-ethyl-3-methylimidazolium bromide (EmimBr), N-butylpyr-idinium bromide (BPyBr), or N-ethylpyridinium bromide (EtPyBr). Compared with the analogous re-action performed over a ZnCl2 catalyst in the con-ventional solvent dichloromethane, higher regiose-lectivity of the para cycloadduct and excellent yield were achieved at shorter reaction time in these ionic liquids with optimized molar compositions of MX and ZnCl2. These moisture-insensitive ionic liquids can be easily separated from reaction products after simple washing with hexane, allowing their reuse with no obvious loss in activity