Copper-Catalyzed Decarboxylative [3 + 2] Annulation of Ethynylethylene Carbonates with Azlactones: Access to γ-Butyrolactones Bearing Two Vicinal Quaternary Carbon Centers.

An efficient decarboxylative [3 + 2] annulation reaction of ethynylethylene carbonates and azlactones has been developed with a copper salt as catalyst. This practical methodology gives access to a diverse library of γ-butyrolactones bearing α,β-two vicinal quaternary carbon centers in good to high yields with good levels of diastereoselectivities (up to 98% yield, >95:5 dr). Preliminary trials on enantioselective variant with a chiral PyBox ligand provided chiral products in up to 71% ee. This synthetic method features mild reaction conditions, broad functional group tolerance, large-scale synthesis, and versatile products transformation. A plausible catalytic cycle for the protocol is proposed based on previous related studies and our experimental observations.