A Hypervalent Cyclic Dibenzoiodolium Salt as a Halogen‐Bond‐Donor Catalyst for the [4+2] Cycloaddition of 2‐Alkenylindoles

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.

Sulfonium and Selenonium Salts as Noncovalent Organocatalysts for the Multicomponent Groebke–Blackburn–Bienaymé Reaction

“…Among the XB donor species, the iodine derivatives are shown to exhibit the highest catalytic activity. Although search for new uncharged iodine-containing XB-donating species is going on, it has been clearly demonstrated that noncovalent organocatalysts based on cationic iodine­(I) , and iodine­(III) − derivatives exhibit the highest catalytic activity (Figure A−C).…”

Diaryliodonium Tetracyanidometallates Self-Assemble into Halogen-Bonded Square-Like Arrays

“…Diaryliodonium cations (Ar 2 I + ) are multipurpose reagents in organic synthesis. They have received major attention as arylating agents − but attracted interest also as topochemical reagents and noncovalent catalysts. − Their ability to form attractive interaction was recognized long ago, when Alcock introduced the concept of secondary bonding . After the rationalization of these interactions as charge-assisted halogen bonds (HaBs), the use of diaryliodonium cations as tectons in crystal engineering became more and more common. , This increased interest was favored by the unique geometric features of these HaB donors with respect to other organic tectons.…”

Chemistry of 2-vinylindoles: synthesis and applications

“…84 Similar [4 + 2] cycloaddition reactions catalyzed by cationic halogen-bond donors to generate 3-indolyl-substituted tetrahydrocarbazole derivatives were obtained in good to excellent yields. 91 Additionally, Diels-Alder reaction of 2-vinylindoles with 3-nitrocoumarins has been discussed to prepare different coumarin-fused polycyclic indoles in good yields (up to 82%) with high diastereoselectivities (up to 419 : 1) in a Brønsted acid. 1…”