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.