Cobalt-Catalyzed Arylative Cyclization of Acetylenic Esters and Ketones with Arylzinc Reagents through 1,4-Cobalt Migration

1,4-Migrations of organopalladium and organorhodium species have been utilized for the development of various cascade reactions involving remote C-H bond activation. Recently, we reported a cobalt-catalyzed migratory arylzincation reaction of an alkyne that features alkenyl-to-aryl 1,4-cobalt migration and cobalt-to-zinc transmetalation as key steps. We report herein that the cobalt/arylzinc combination can also promote a cascade arylative cyclization reaction of alkynes bearing pendant ester or ketone moieties to afford benzo-fused cyclic ketone or alcohol products, respectively. The reaction is considered to proceed through insertion of the alkyne into an arylcobalt species, 1,4-cobalt migration, and intramolecular organocobalt addition to the carbonyl group. The present cobalt/arylzinc system may not only serve as an alternative to previously reported rhodium/arylboron and iridium/arylboron systems but also complement their scopes in the arylative cyclization.