Synthesis of 2,3-Benzotropones via Palladium(II)-Catalyzed Aerobic Dehydrogenation from 1-Benzosuberones and Sequential Diels-Alder Reaction to Yield Benzobicyclo[3.2.2]nonenones.

An approach to 2,3-benzotropone from 1-benzosuberone via palladium(II)-catalyzed aerobic dehydrogenation was developed. This method first provided a catalytic route to various 2,3-benzotropones from their corresponding 1-benzosuberones in good yields. In addition, the reaction could be applied to a one-pot Diels-Alder reaction with maleimide, providing a complex benzobicyclo[3.2.2]nonenone in ≤90% yield. Kinetic analysis supporting our proposed mechanism was also performed, underscoring the robustness of the developed synthetic pathway.

Synthesis of Xanthones via Copper(II)-Catalyzed Dehydrogenative Cyclization and Successive Aromatization in a One-Step Sequence.

In this study, an unprecedented approach to the xanthone scaffold from cyclohexyl(2-hydroxyphenyl)methanone via dehydrogenative cyclization and a successive aromatization cascade is reported. This methodology affords a novel route to the privileged structure with a wide substrate scope (a total of 29 compounds, ≤96% yield) in a highly atom-economic manner.

Syntheses of 1H-Indoles, Quinolines, and 6-Membered Aromatic N-Heterocycle-Fused Scaffolds via Palladium(II)-Catalyzed Aerobic Dehydrogenation under Alkoxide-Free Conditions.

Aromatic N-heterocycle-fused scaffolds such as indoles and quinolines are important core structures found in various bioactive natural products and synthetic compounds. Recently, various dehydrogenation methods with the help of alkoxides, known to significantly promote dihydro- or tetrahydro-heterocycles to be oxidized, were developed for the heterocycle synthesis. However, these approaches are sometimes unsuitable due to resulting undesired side reactions such as reductive dehalogenation. Herein, expedient syntheses of 1H-indoles, quinolines, and 6-membered N-heterocycle-fused scaffolds from their hydrogenated forms through palladium(II)-catalyzed aerobic dehydrogenation under alkoxide-free conditions are reported. A total of 48 compounds were successfully synthesized with a wide range of functional groups including halogens (up to 99% yield). These methodologies provide facile routes for various privileged structures possessing aromatic N-heterocycles without the help of alkoxides, in highly efficient manners.

Synthesis of meta-(Indol-3-yl)phenols from Indoles and Cyclohexenone via Palladium(II)-Catalyzed Oxidative Heck Reaction and Dehydrogenative Aromatization in a One-Step Sequence.

Facile construction of a meta-(indol-3-yl)phenol framework with a wide substrate scope (a total of 25 compounds) via a palladium(II)-catalyzed oxidative Heck reaction and dehydrogenative aromatization in a one-step sequence is reported. This methodology affords a novel route for the privileged structures that are challenging to access via a direct link between indole and phenol, in a highly efficient and atom-economical manner.