HfCl4-Catalyzed [4+2] Cycloaddition of β,γ-Unsaturated α-Keto Esters with Alkynes

Herein we report Lewis acid HfCl4-catalyzed [4 +2] cycloaddition between beta,gamma-unsaturated alpha-keto esters and varioussymmetric or unsymmetric alkynes, giving the desired polysub-stituted 4H-pyrans in up to 98% yield and with excellentregioselectivity (>99:1) via a vinyl carbocation under mild conditions

Automated summary

This study reports a [4+2] cycloaddition catalyzed by Lewis acid HfCl4, leading to high yields of polysubstituted 4H-pyrans. The reaction conditions are mild and exhibit excellent selectivity.