Resumen de Cyclization of the Monoterpene Citronellal to Isopulegol:: A Biomimetic Natural Product Synthesis

Bruce L. Jensen, Ahmed Malkawi, Vanessa McGowan

• Cyclization of the monoterpene (S)-(--)-citronellal takes place rapidly in the presence of tin(IV) chloride in methylene chloride at 0 °C, affording the cyclic monoterpene isopulegol in a yield of 85%. The experiment reported here mimics the reaction found in the biosynthetic pathway leading to another well-known natural product, menthol. The starting material and final product display easily interpreted infrared and proton-NMR spectra. Coupling patterns and constants produced by the C-3 methine proton establish the all-equatorial substitution pattern of the cyclohexane ring system found in the product. Either a carbocation process or an ene reaction can be used to describe the mechanistic details of this reaction.