The orthoester Johnson–Claisen rearrangement of allylic terpenols in the presence of acidic ionic liquid

Abstract A convenient protocol for the synthesis of natural isoprenoid-derived carboxylic esters via reaction of allylic terpenols with triethyl orthoacetate (propionate) in the presence of 1-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF 6 ] (10 mol%), has been developed. The desired terpene derivatives were prepared in moderate to high yield. The ionic liquid (IL) can be easily separated from the products and repeatedly used up to ten times without reduction in the product yield. Experimental data evidence that HF, generated in situ from the IL, most likely acts as a true catalyst in the Johnson–Claisen rearrangement.