Formal Lossen Rearrangement/Alkenylation or Annulation Cascade of Heterole Carboxamides with Alkynes Catalyzed by CpRhIII Complexes with Pendant Amides |
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Authors: | Takayuki Yamada Dr Yu Shibata Prof Dr Ken Tanaka |
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Institution: | Department of Chemical Science and Engineering, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo, 152-8550 Japan |
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Abstract: | It has been established that a cyclopentadienyl (Cp) RhIII complex with two aryl groups and a pendant amide moiety catalyzes the formal Lossen rearrangement/alkenylation cascade of N-pivaloyl heterole carboxamides with internal alkynes, leading to alkenylheteroles. Interestingly, the use of sterically demanding internal alkynes afforded not the alkenylation but the 3+2] annulation products (5,5]-fused heteroles). In these reactions, the pendant amide moiety of the CpRhIII complex may accelerate the formal Lossen rearrangement. The use of five-membered heteroles may deter reductive elimination to form strained 5,5]-fused heteroles; instead, protonation proceeds to give the alkenylation products. Bulky alkyne substituents accelerate the reductive elimination to allow the formation of the 5,5]-fused heteroles. |
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Keywords: | alkenylation C−H activation cyclopentadienyl ligands Lossen rearrangement rhodium |
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