Open–Close: An Alternative Strategy to α‑Functionalization of Lactone via Enamine Catalysis in One Pot under Mild Conditions

An open–close strategy in asymmetric catalysis is newly developed. With this powerful strategy, lactols are directly applied as potential precursors of lactones in enamine-based asymmetric Michael reactions providing a facile access to α-functionalized lactones containing two adjacent stereogenic centers as a single diastereomer in good to excellent yields (up to 99%) and with excellent enantioselectivities (most cases >99%). Moreover, the reaction products are shown to give highly functionalized derivatives by stepwise systematic transformations.