Ligand-Enabled Sequential C(sp3)-H and C(sp2)-H Diolefination Reaction via Palladium Catalyst

Assembly of 2-Substituted Tetrahydroquinolines from ortho-Methylbenzenesulfamides and Dienes, Using a C(sp3)-H Activation/Annulation Sequence

1,2,3,4-Tetrahydroquinolines (THQs) are essential structural cores in many natural products and pharmaceutical drugs. Especially relevant are those presenting substitutions at position 2, yet practical methods for their one-step assembly from acyclic precursors are very scarce. Herein, we present a straightforward approach to assembling these skeletons from ortho-methylanilines using a palladium-catalyzed C(sp3)-H activation/formal cycloaddition sequence. Key for the success of the approach is the use of dienes as partners, since they lead to stable π-allyl palladium intermediates that prevent β-hydride elimination processes and allow installation of versatile alkenyl handles at position 2. Moreover, installing a perfluorobenzenesulfonyl substituent at the amine not only facilitates the C-H activation but also allows for an easy recovery of the free amine.

Palladium(II)-Catalyzed Nondirected Late-Stage C(sp2)-H Deuteration of Heteroarenes Enabled Through a Multi-Substrate Screening Approach

The importance of deuterium labelling in a variety of applications, ranging from mechanistic studies to drug-discovery, has spurred immense interest in the development of new methods for its efficient incorporation in organic, and especially in bioactive molecules. The five-membered heteroarenes at the center of this work are ubiquitous motifs in bioactive molecules and efficient methods for the deuterium labelling of these compounds are therefore highly desirable. However, the profound differences in chemical properties encountered between different heteroarenes hamper the development of a single set of broadly applicable reaction conditions, often necessitating a separate optimization campaign for a given type of heteroarene. In this study we describe the use of a multi-substrate screening approach to identify optimal reaction conditions for different classes of heteroarenes from a minimal number of screening reactions. Using this approach, four sets of complementary reaction conditions derived from our dual ligand-based palladium catalysts for nondirected C(sp2)-H activation were identified, that together enable the deuteration of structurally diverse heteroarenes, including bioactive molecules.

Palladium-Catalyzed (3 + 2) Annulation of Aromatic Acids by C(sp3)-H Olefination and Decarboxylative Cross-Coupling Reaction

A palladium-catalyzed (3 + 2) annulation of 2-methylbenzoic acid with maleimide using Ac-Leu-OH as a powerful ligand has been reported. Through a site-selective γ-C(sp3)-H olefination reaction and a sequential decarboxylative cross-coupling reaction, a five-membered cyclic ring was obtained as the final product. This novel reaction features great site selectivity and reactivity to generate various cyclic products in moderate to good yields.