Aza Diels-Alder Reactions of Nitriles, N,N-Dimethylhydrazones, and Oximino Ethers. Application in Formal [2 + 2 + 2] Cycloadditions for the Synthesis of Pyridines.

Metal-free, formal [2 + 2 + 2] cycloaddition strategies for the synthesis of polycyclic pyridine derivatives are described. The overall transformation proceeds via a two-stage pericyclic cascade mechanism. In the first step, an intramolecular propargylic ene reaction generates a vinylallene that is necessarily locked in the s-cis conformation.

Terminal-Selective Functionalization of Alkyl Chains by Regioconvergent Cross-Coupling.

Hydrocarbons are still the most important precursors of functionalized organic molecules, which has stirred interest in the discovery of new C-H bond functionalization methods. We describe herein a new step-economical approach that enables C-C bonds to be constructed at the terminal position of linear alkanes. First, we show that secondary alkyl bromides can undergo in situ conversion into alkyl zinc bromides and regioconvergent Negishi coupling with aryl or alkenyl triflates.

Palladium-catalyzed β-arylation of silyl ketene acetals and application to the synthesis of benzo-fused δ-lactones.

Silyl ketene acetals are shown to be competent nucleophiles in Pd-catalyzed migrative C(sp(3))-H arylations. Compared to the parent ester lithium enolates, they possess decreased reactivity but enhanced chemoselectivity. This behavior was exploited through the synthesis of valuable benzo-fused δ-lactones such as 1-isochromanones and dihydrocoumarins.