Pd-Catalyzed Regio- and Stereoselective Synthesis of Tertiary Enamides via a Three-Component Coupling of 2-Arylaziridines with Diazo Esters and Cyclic Ethers

A palladium-catalyzed three-component coupling of 2-arylaziridines, α-diazo esters, and cyclic ethers, affording tertiary enamides with excellent regio- and stereoselectivity, is reported. This regioselective ring-opening of aziridines is different from the classical transition-metal/phosphine catalyzed ones. A broad spectrum of substrates is tolerated (up to 33 examples). An ortho-aryl substituent on the naphthyl ring of 1,1'-bi-2-naphthol (BINOL)-derived phosphoramidite ligand is critical for this coupling, and the additional diphosphine (DPEphos) ligand can further enhance the reactivity. Mechanistic studies suggest that 10-membered and 9-membered palladacycle intermediates may be formed and followed by twice reversible β-H eliminations.