Zn(II)-Catalyzed Addition of Aromatic/Heteroaromatic C(sp2)−H to Azoalkenes: A Polarity-Reversed Arylation of Carbonyl Compounds

The α-(hetero)arylation of ketones and their derivatives by the direct installation of (hetero)aryl substituents at the α-carbon atom on the carbonyl structure is a challenging goal in organic synthesis, but its utility is limited to use of stoichiometric amount of base, expensive noble metal catalysts, prefunctionalized (hetero)arenes, bulky ligands and high temperatures. Here, we reported how an umpolung approach that involve the Michael-type reaction between electron-rich (hetero)aromatic substrates and azoalkenes provided access to otherwise inaccessible hydrazone structures. Subsequent hydrolysis of these latter to ketones as well as the other valuable synthetic transformations to a variety of heterocyclic scaffolds (including precursor of indole-indoline core of the vinca alkaloids (+)-vinblastine and (+)-vincristine) demonstrated the usefulness of this protocol.