Reverse Regioselective Cp*Co(III)-Catalyzed [4 + 2] C-H Annulation of N-Chloroamides with Vinylsilanes: Synthesis of 4-Silylated Isoquinolones and Their Synthetic Utilities.

We have developed a Cp*Co(III)-catalyzed reverse regioselective [4 + 2] annulation of N-chlorobenzamides/acrylamides with vinylsilanes for the synthesis of 4-silylated isoquinolones. The reaction was performed at ambient temperature under redox-neutral conditions. The reaction utilized the N-Cl bond as an internal oxidant, furnished the required products with excellent regioselectivities, and demonstrated high functional group tolerance. The synthetic utility of 4-silylated isoquinolones has been demonstrated for the preparation of 4-heteroarylated and 4-alkylated isoquinolones via metal-free C-C couplings. Additionally, 3,4-dihydroisoquinolones were synthesized via protodesilylation of 4-silylated isoquinolones, thus making vinylsilane an ethylene surrogate.

Harnessing Vinyl Acetate as an Acetylene Equivalent in Redox-Neutral Cp*Co(III)-Catalyzed C-H Activation/Annulation for the Synthesis of Isoquinolones and Pyridones.

We have developed Cp*Co(III)-catalyzed redox-neutral synthesis of 3,4-unsubstituted isoquinoline 1(2H)-ones at ambient temperature using N-chloroamides as a starting material. The reaction utilizes vinyl acetate as an inexpensive and benign acetylene surrogate. The N-Cl bond of the N-chlorobenzamides plays the role of an internal oxidant and hence precludes the need for an external oxidant. The reaction works with a wide range of substrates having various functional groups and a substrate containing a heterocyclic ring. Notably, the reaction is extended to the N-chloroacrylamides in which vinylic C-H activation occurs to furnish the 2-pyridone derivatives. Preliminary mechanistic studies were also conducted to shed light on the mechanism of this reaction.