Cobalt-NHC Catalyzed C(sp2)-C(sp3) and C(sp2)-C(sp2) Kumada Cross-Coupling of Aryl Tosylates with Alkyl and Aryl Grignard Reagents

The first cobalt-catalyzed cross-coupling of aryl tosylates with alkyl and aryl Grignard reagents is reported. The catalytic system uses CoF3 and NHCs (NHC=N-heterocyclic carbene) as ancillary ligands. The reaction proceeds via highly selective C-O bond functionalization, leading to the corresponding products in up to 98 % yield. The employment of alkyl Grignard reagents allows to achieve a rare C(sp(2))-C(sp(3)) cross-coupling of C-O electrophiles, circumventing isomerization and beta-hydride elimination problems. The use of aryl Grignards leads to the formation of biaryls. The C-O cross-coupling sets the stage for a sequential cross-coupling by exploiting the orthogonal selectivity of the catalytic system.