Efficient Enantioselective Synthesis of Functionalized Tetrahydropyrans by Ru-Catalyzed Asymmetric Ring-Opening Metathesis/Cross-Metathesis (AROM/CM)

An efficient method for enantioselective synthesis of highly functionalized pyrans (up to 98% ee) through Ru-catalyzed asymmetric ring-opening metathesis/cross-metathesis is described. Reactions are promoted by a recyclable chiral Ru−chloride or a new chiral Ru−iodide complex; the latter catalyst is less efficient but gives rise to significantly higher levels of enantioselectivity. Catalytic reactions can be performed in undistilled solvent and with a wide range of substrates, including those that contain secondary and tertiary alcohols. Representative regioselective functionalizations that highlight the utility of the catalytic method are also presented.