Cobalt-Catalyzed Addition of Arylzinc Reagents to Alkynes to Form ortho-Alkenylarylzinc Species through 1,4-Cobalt Migration

摘要

Metal migration reactions through C—H bond activation, Immigrations in particular, have attracted significant attention in organorhodium and organopalladium chemistry not only as mechanistically intriguing processes but also as entries to novel remote C—H bond functionalization reactions.After the first observation of 1,4-rhodium migration in the reaction of an arylboronic acid with norbornene by Miura et al. , Hayashi and co-workers reported that a rhodium-catalyzed hydroarylation reaction of an alkyne with an arylboronic acid involves insertion of the alkyne into an arylrhodium species, vinyl-to-aryl 1,4-rhodium migration, and protonation of the resulting ortho-alkenylarylrhodium species (Scheme 1 a). These seminal studies set the stage for the subsequent development of domino cyclization reactions involving 1,4-rhodium migration followed by trapping of the arylrhodium species with an internal electrophile (e.g., carbonyl group). Herein, we report on a cobalt-catalyzed reaction of an arylzinc reagent with an alkyne that involves a similar vinyl-to-aryl 1,4-cobalt migration but is unique in that the Immigration is followed by transmetalation with the arylzinc reagent (Scheme lb). Trapping of the resulting ortho-alke-nylarylzinc species with external electrophiles allows access to a variety of 1-alkenyl-arenes functionalized in the 2-position, many of which are not readily accessible by existing synthetic methods.