Electrophilic Activation of Iodonium Ylides by Halogen-Bond-Donor Catalysis for Cross-Enolate Coupling

The umpolung alkylation of silyl enol ethers with an iodonium(III) ylide proceeds under mild conditions to afford various 1,4-dicarbonyl compounds in high yields in the presence of a halogen-bonding catalyst. Unlike typical transition-metal activation processes of such ylide precursors, which tend to proceed via carbenoid intermediates, experimental and computational studies indicate that halogen bonding (XB) between the XB donor catalyst and the iodonium ylide plays a crucial role in promoting the reaction. The identification of a compatible Bronsted base catalyst enabled the extension of this method to enols generated in situ to give the corresponding adducts in good yields.