In a recent JACS Communication [Bolla et al., J. Am. Chem. Soc. 2005, 127, 16044], the Rychnovsky group reports a new annulation reaction that generates tetrahydropyran rings as single diastereomers from unsaturated ketones and enol ether alkenes. The reaction is stereoselective and should be useful for synthesizing natural products containing tetrahydropyran rings.