Enantioselective Oxidative Cyclization/Mannich Addition Enabled by Gold(I)/Chiral Phosphoric Acid Cooperative Catalysis.

An enantioselective Mannich-type reaction of 3-butynol and nitrones is described, which affords dihydrofuran-3-ones in good yields and with excellent enantioselectivities. The reaction is initiated by gold-catalyzed alkyne oxidation and modification of the resulting gold carbene species with a tethered hydroxy group to form enolate species; the reaction terminates with an enantioselective Mannich-type addition with the assistance of chiral phosphoric acid (CPA) and hydrogen bonding. This novel pattern of alkyne transformation involving chemical bond cleavage, and a fragment modification and reassembly process, provides an atom- and step-economic method, and is the first example of cooperative asymmetric catalysis in gold-catalyzed alkyne oxidations via an alpha-oxo gold carbene route.