A Hypervalent Cyclic Dibenzoiodolium Salt as a Halogen‐Bond‐Donor Catalyst for the [4+2] Cycloaddition of 2‐Alkenylindoles. Issue 5 (3rd May 2021)

• Record Type: Journal Article
• Authors: Nishida, Yuki; Suzuki, Takumi; Takagi, Yuri; Amma, Emi; Tajima, Ryoya; Kuwano, Satoru; Arai, Takayoshi
• Is Part Of: ChemPlusChem. Volume 86:Issue 5(2021)
• Page Start: 741
• Page End: 744
• Publication Date: 2021-05-03
• Subjects: [4+2] cycloaddition reactions -- halogen bonding -- homogeneous catalysis -- hypervalent iodine -- indoles; Chemistry -- Periodicals; 540.5
• DOI: 10.1002/cplu.202100089
• Languages: English
• ISSNs: 2192-6506

Abstract

Abstract: A stable, hypervalent cyclic dibenzoiodolium salt acted as a strong halogen bonding (XB)‐donor catalyst for [4+2] cycloaddition of 2‐alkenylindoles, and not as an oxidizing agent. The cross‐[4+2] cycloaddition of 2‐vinylindoles with 2‐alkenylindoles was catalyzed smoothly by the hypervalent cyclic dibenzoiodolium triflate catalyst to give the tetrahydrocarbazoles in up to 99 % yield with 17 : 1 diastereoselectivity. The hypervalent cyclic dibenzoiodolium salt was also applicable to the Povarov reaction of 2‐vinylindole with N ‐ p ‐methoxyphenyl (PMP) imine to give the indolyl‐tetrahydroquinoline in 83 % yield. Abstract : Cat not ox : A trivalent cyclic dibenzoiodolium salt that does not act as an oxidizing agent becomes a halogen bonding (XB)‐donor catalyst. Using the I(III)‐XB catalyst (see scheme), a cross‐[4+2] cycloaddition of 2‐vinylindoles with 2‐alkenylindoles was furnished to give 3‐indolyl‐substituted tetrahydrocarbazoles in highly diastereoselective manner.