Rhodium-Catalyzed Cascade Oxidative Annulation Leading to Substituted Naphtho[1,8-bc]pyrans by Sequential Cleavage of C(sp2)–H/C(sp3)–H and C(sp2)–H/O–H Bonds

The cascade oxidative annulation reactions of benzoylacetonitrile with internal alkynes proceed efficiently in the presence of a rhodium catalyst and a copper oxidant to give substituted naphtho­[1,8-bc]­pyrans by sequential cleavage of C­(sp2)–H/C­(sp3)–H and C­(sp2)–H/O–H bonds. These cascade reactions are highly regioselective with unsymmetrical alkynes. Experiments reveal that the first-step reaction proceeds by sequential cleavage of C­(sp2)–H/C­(sp3)–H bonds and annulation with alkynes, leading to 1-naphthols as the intermediate products. Subsequently, 1-naphthols react with alkynes by cleavage of C­(sp2)–H/O–H bonds, affording the 1:2 coupling products. Moreover, some of the naphtho­[1,8-bc]­pyran products exhibit intense fluorescence in the solid state.