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.