Rhodium-Catalyzed Cascade Oxidative Annulation Leading to Substituted Naphtho[1,8-bc]pyrans by Sequential Cleavage of C(sp~2)-H/C(sp~3)-H and C(sp~2)-H/O-H Bonds

摘要

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[l,8-bc]pyrans by sequential cleavage of C(sp~2)-H/C(sp~3)-H and C(sp~2)-H/O-H bonds. These cascade reactions are highly regio-selective with unsymmetrical alkynes. Experiments reveal that the first-step reaction proceeds by sequential cleavage of C(sp~2)-H/C(sp~3)-H bonds and annulation with alkynes, leading to 1-naphthols as the intermediate products. Subsequently, 1-naphthols react with alkynes by cleavage of C(sp~2)-H/O-H bonds, affording the 1:2 coupling products. Moreover, some of the naphtho[l,8-bc]pyran products exhibit intense fluorescence in the solid state.