Cobalt-catalyzed Annulation Of C(sp~2)-H Bond With Alkyne By Traceless N,O-Bidentate Directing Group

Substituted isoquinolines are one of the most important heterocycles,which are frequently found in natural products and biologically active molecules.Recently,transition-metal-catalyzed C-H bond activation provides a new approach to obtain isoquinolines.N,O-bidentate directing-enabled,traceless heterocycle synthesis is described via Cp*-free cobalt-catalyzed C-H activation/annulation with both internal and terminal alkynes.This operationally simple approach shows a broad substrate scope with 28 isoquinolines obtained in good to excellent yields.A series of control experiments have been conducted for the plausible reaction mechanism.The N-O moiety of ?-imino-oxy acids which were installed through cheap and commercially available starting materials can serve as internal oxidant.The directing group can be removed directly in situ along the catalytic process,which shows the atom-and step-economy of the catalysis system.Meanwhile,the weakly coordinating nature of the carboxylic acid has played a vital role in the reaction.