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

Herein we report Lewis acid HfCl4-catalyzed [4 + 2] cycloaddition between ß,γ-unsaturated α-keto esters and various symmetric or unsymmetric alkynes, giving the desired polysubstituted 4H-pyrans in up to 98% yield and with excellent regioselectivity (>99:1) via a vinyl carbocation under mild conditions.

Switchable Enantioselectivity in Conjugate Alkyne Addition of ß,γ-Unsaturated α-Keto Esters by Asymmetric Binary Acid Catalysis.

Switchable enantioselectivity was uncovered in the enantioselective catalytic conjugate addition of ß,γ-unsaturated α-keto esters with terminal alkynes to the chiral Lewis acid complex of In(BF4)3 and chiral phosphoric acid.

Carbocation Lewis Acid TrBF4-Catalyzed 1,2-Hydride Migration: Approaches to (Z)-α,ß-Unsaturated Esters and α-Branched ß-Ketocarbonyls.

Carbocation Lewis acid TrBF4-catalyzed 1,2-hydride migration of α-alkyldiazoacetates themselves or in situ-generated cross-coupling adducts of aldehydes and α-alkyldiazoacetates has been developed, affording (Z)-α,ß-unsaturated esters and α-branched ß-ketocarbonyls, respectively, in good yields and with high regioselectivities.