Diastereo‐ and Enantioselective Synthesis of trans‐2,3‐Disubstituted 2,3‐Dihydropyran‐4‐one Derivatives

trans‐Diastereoselective hetero‐Diels–Alder reactions took place in the presence of SiCl₄/activator systems. The reactions of aldehydes with a derivative of Danishefsky’s diene afforded the corresponding pyrones with high yields and diastereoselectivity upon activating SiCl₄ with suitable neutral Lewis bases. Aldol intermediates deriving from a Mukaiyama‐type pathway were isolated in many cases. The employment of a chiral activator allowed us to convert Danishefsky’s diene (or its disubstituted derivative) into both aldols and pyrones in good to high enantiomeric excesses.