Stereoselective Insertion of Ketenes into O,O‐Acetals: Synthesis of β‐Alkoxy Esters and 1,4‐Dioxepan‐5‐ones

High stereoselectivity earmarks the Lewis acid catalyzed insertion of ketenes in chiral acetals. The anti-configurated aldol products 2 are formed from 1 with more than 95% stereoselectivity. A wide range of ketenes and acetals can be used, which enables the synthesis of interesting heterocycles.