Copper-Catalyzed Stereoselective [4 + 2] Cycloaddition of β,γ-Unsaturated α-Keto Esters and 2-Vinylpyrroles in Water.

An asymmetric [4 + 2] cycloaddition of β,γ-unsaturated α-keto esters with 2-vinylpyrroles in water was developed under the catalysis of a kind of copper complex with a low loading. A series of optically pure 3,4-dihydro-2 H -pyran derivatives could be obtained in excellent yields, with high diastereoselectivities and enantioselectivities. The corresponding mechanism was proposed, which was supported by DFT calculations.