Synthesis of Enantiomerically Pure 2,3,4,6‐Tetrasubstituted Tetrahydropyrans by Prins‐Type Cyclization of Methyl Ricinoleate and Aldehydes

The AlCl3‐catalyzed Prins‐type cyclization of methyl ricinoleate (1), an enantiomerically pure renewable compound, with aldehydes such as heptanal (2a), isobutyraldehyde (2b), pivaldehyde (2c) and benzaldehyde (2d) is a simple reaction for the diastereoselective synthesis of enantiomerically pure 2,3,6‐trialkyl‐substituted 4‐chlorotetrahydropyrans. The respective 4‐hydroxytetrahydropyrans are obtained e.g. with aldehydes 2a and 2d using montmorillonite KSF/O as the catalyst. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)