Manganese(III)‐Catalyzed Oxidative Cyclization of Aryl 1‐Cyanoalk‐5‐ynyl Ketone Systems: A Convenient and General Approach to Cyclopenta[b]naphthalene Derivatives

A convenient and general approach for cyclopenta[b] naphthalene derivatives containing a structurally diverse functionality at C-4 position has been successfully developed, whereby manganese(III) acetate plays a key role to facilitate the tandem 5-exo-dig and 6-exo/endo cyclization in an efficient manner. Various functional groups, including trimethyl silyl, aryl, ester, ketone, secondary/tertiary amide, phosphonate and halogen, capped on the terminal acetylenic unit are well tolerated under optimal reaction conditions. It is highly conceivable that this novel [6.6.5] framework formation procedure may have broad synthetic utility in light of its operational simplicity and high yields.