Hydroxyl-Directed Rh(III)-Catalyzed C-H Functionalization: Access to Benzo[ de ]chromenes.

A cascade oxidative annulation reaction of heterocyclic ketene aminals (HKAs) with internal alkynes catalyzed by [Cp*RhCl 2 ] 2 and oxidized by Cu(OAc) 2 ·H 2 O was developed to efficiently synthesize highly functionalized benzo[ de ]chromene derivatives in good to excellent yields. The reaction proceeded by the sequential cleavage of C(sp 2 )-H/O-H and C(sp 2 )-H/C(sp 2 )-H bonds. These multicomponent cascade reactions were highly regioselective. In addition, all of the benzo[ de ]chromene products exhibited intense fluorescence emission in the solid state, and they demonstrated concentration-dependent quenching in the presence of Fe 3+ , indicating that these compounds could be used in the recognition of Fe 3+ .