Iodine(III)-Enabled Distal C–H Functionalization of Biarylsulfonanilides

Abstract

Here we report a metal-free C-N coupling reaction for carbazole synthesis by distal (- meta) C-H bond functionalization. Nitrenium ion, a potential synthetic intermediate, was generated in situ from reactions of iodine(III) reagents and biarylsulfonanilides. Following, nitrenium ions were used for intramolecular dehydrogenative C-N coupling reactions via 1,2-alkyl (methyl or ethyl) migration by the expense of C-H bond functionalization at the distal position toward synthesis of 1,2,4-trialkyl-substituted carbazoles. The iodine(III) condition was either maintained by using a stoichiometric amount of phenyliodine diacetate (PIDA) or in-situ generated from iodobenzene (PhI)- meta-chloroperbenzoic acid ( mCPBA) combination.

Hypervalent iodine-mediated synthesis and late-stage functionalization of heterocycles

“…Later, the same group developed intramolecular dehydrogenative C−N coupling reaction for the synthesis of carbazoles 264 by reacting biarylsulfonanilides 273 with iodine(III) reagent (Scheme 73). 104 This method enabled distal (-meta) C−H bond functionalization with the aid of 1,2-alkyl migration. Reactions were performed either by using stoichiometric phenyliodine diacetate 6 or in situ generated iodine(III) reagent from precatalyst iodobenzene 13 (20 mol %) and terminal oxidant mCPBA.…”

“…Murai and co-workers performed the first oxidative rearrangement of cyclic secondary amines 274 using hypervalent iodine reagent 6 (Scheme 74). 105 This method comprises PhI(OAc)2-promoted 1,2-C-to-N alkyl migration of secondary amines 274 followed by subsequent reduction using NaCNBH3 to provide tetracyclic compounds 275. Further scope of the reaction was extended towards the synthesis of macrocyclic indole-fused compounds.…”

Recent Advances in Intramolecular Metal‐Free Oxidative C–H Bond Aminations Using Hypervalent Iodine(III) Reagents

“…Recently, carbazole synthesis has been reported by a distal (‐ meta ) C–H bond functionalization of biarylsulfonanilides using in situ generated PIDA from iodobenzene and meta ‐chloroperbenzoic acid or a stoichiometric amount of phenyliodine diacetate (PIDA) …”

C–N Coupling via Antiaromatic Endocyclic Nitrenium Ions

“…The combinations of amine or amine derivatives with hypervalent iodine­(III) reagents − generally produce nitrenium ions. , The divalent nitrogen-containing species with six electrons in its valence shell with positive charge on nitrogen is recognized as a nitrenium ion (Figure a). , Nitrenium ions are isoelectronic with carbene family having two nonbonding electrons. The nitrenium ion is considered as one of the most important synthetic intermediates in innumerable chemical transformations. − Depending on the nature and stability of the nitrenium ion, many oxidative transformations are reported for the preparation of functional molecules of interests using exocyclic nitrenium ions. , Due to the electron spin orientation, nitrenium ions exist in two different forms, i.e., singlet state and triplet state (Figure a) . In Figure b, generation of a nitrenium ion is shown from the mixtures of amine or amide with iodine­(III) reagents.…”