Nickel-Catalyzed Cycloaddition of α,β,γ,δ-Unsaturated Ketones with Alkynes

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 β,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.

A palladium catalyzed stereo-convergent aminocarbonylation of 1,3-dienes with nitroarenes: synthesis of (E,E)-dienamides

A palladium catalyzed stereo-convergent aminocarbonylation of 1,3-dienes with nitroarenes has been developed. The reaction of mixtrues of E/Z isomers of 1,3-dienes reacted with nitroarenes and produced (E,E)-dienamides with high stereoselectivities.

Synthesis of (E,E)-Dienones and (E,E)-Dienals via Palladium-Catalyzed γ,δ-Dehydrogenation of Enones and Enals

A new strategy for the synthesis of conjugated (E,E)-dienones and (E,E)-dienals via a palladium-catalyzed aerobic γ,δ-dehydrogenation of enones and enals has been developed. The method can be employed in the direct and efficient synthesis of various (E,E)-dienones and (E,E)-dienals, including non-substituted α-, β-, and γ- and/or δ-substituted (E,E)-dienones and (E,E)-dienals. The protocol is featured by the ready accessibility and elaboration of the starting materials, good functional group compatibility, and mild reaction conditions. Furthermore, the reaction is of complete E,E-stereoselectivity and uses molecular oxygen as the sole clean oxidant.

1,3-Dienones and 2H-Pyran-2-ones from Soft α-Vinyl Enolization of β-Chlorovinyl Ketones: Defined Roles of Brönsted and Lewis Base

The eliminative reaction pathways of (E)-β-chlorovinyl ketones were investigated in the presence of both Brönsted and Lewis bases. The Brönsted base, Et3N, effected the soft α-vinyl enolization of (E)-β-chlorovinyl ketones to [3]cumulenol intermediates; in turn, a catalytic amount of Lewis base, PPh3, initiated isomerization to provide 1,3-dienones in high yields. The introduction of a carbon-based nucleophile into the reaction mixture provided the highly efficient synthetic route to 2H-pyran-2-ones in one pot, where the carbon-based nucleophile generated by an extra equivalent of Brönsted base, Et3N, attacked the electrophilic [3]cumulenol intermediates to initiate cyclization to give 2H-pyran-2-ones.