Oxidative Annulation of Acetanilides with Alkynes Catalyzed by Cyclopentadienyl Rhodium(III) Complexes with Pendant Amides

Abstract

AbstractIt has been established that a cationic cyclopentadienyl (Cp) rhodium(III) complex with a pendant N‐phenylcarbamoyl moiety (CpA1RhIII) showed high catalytic activity towards the oxidative [3+2] annulation of acetanilides with internal alkynes to produce substituted indoles. Catalytic activity of the CpA1RhIII complex in the reactions of symmetric internal alkynes (diphenylacetylene and 6‐dodecyne) was higher than that of the Cp*‐rhodium(III) complex and comparable to that of a Cp‐rhodium(III) complex with two ethoxycarbonyl groups (CpERhIII). On the other hand, the CpA1RhIII complex showed significantly higher catalytic activity than the CpERhIII complex in the reactions of unsymmetric internal alkynes (1‐phenyl‐1‐propyne and 1‐phenyl‐1‐hexyne). Additionally, the catalytic activity of the CpA1RhIII complex in the oxidative tandem [2+2+2] annulation‐lactamization of acetanilides with two unsymmetric electron‐deficient internal alkynes (ethtyl 2‐butynoate) was also comparable to that of the CpERhIII complex.