Cp*Co(III)-Catalyzed C(sp³)–H Bond Activation: A Highly Stereoselective and Regioselective Alkenylation of 8-Methylquinoline with Alkynes

Abstract

Efficient, atom-economical, highly regioselective C­(sp3)–H bond alkenylation of 8-methylquinoline catalyzed by (Cp*)­Co­(III) is reported. A well-defined, air-stable, molecular cobalt catalyst, Cp*Co­(III), is employed for the first time in C­(sp3)–H bond activation. The developed methodology is broadly applicable and tolerates a variety of functional groups, under mild conditions. Experimental and density functional theory (DFT) results suggest that the initial cyclometalation was occurred via an external-base-assisted concerted metalation deprotonation pathway.

Cobalt catalyzed carbonylation of unactivated C(sp3)–H bonds

“…16 n We have previously demonstrated the activation of C(sp 3 )–H bonds using Cp*Co( iii ) for C–H alkenation with alkynes and C–H amidation with oxazolone. 18 Inspired by these results and based on our continuous efforts on the development of cobalt catalyzed C–H bond functionalization, 19 we report herein the first regio- and site-selective cobalt catalyzed carbonylation of unactivated C(sp 3 )–H bonds including terminal and internal C–H bond connected α-1°, 2° and 3° carbons (Scheme 1c). …”

Direct Functionalization of C−H Bonds by Iron, Nickel, and Cobalt Catalysis

“…Not surprisingly, this has been realized on a number of examples, for example, pyrroles and benzamides . The group of Sundararaju used 8‐methylquinoline 206 as starting material, which is the first example of a C(sp 3 )−H alkenylation using this set of reaction conditions (Scheme ) . In most examples R 1 and R 2 were identical with n ‐butyl, which led to high yields between 62–86 % of 207 (14 examples in total).…”

Nickel, Cobalt and Palladium Catalysed C−H Functionalization of Un‐Activated C(sp3)−H Bond

“…From control experiment it is cleared that all three components i. e., Co catalyst, Ag salt and carboxylic acid are required to obtain good yield. When reaction carried for longer period of time yield will increased, whereas by changing counterion from SbF 6 to OTf to propagate alkenylation produces product in 95 % yield within 20 hour, however, changing to PF 6 gives only 76 % yield . Desired product obtained in good yield when 2 mol % of Cp*Co[III] catalyst is used along with 4 mol % of silver salt and admantyl carboxylic acid as an additive at 80 °C for 20 h. (Scheme ) Same year they also reported first time under mild conditions oxidant free Cp*Co(III) catalyzed C(sp 3 )−H bond amidation of 8‐methylquinoline, using oxazolone as an efficient amidating agent.…”