An Organic Intermolecular Dehydrogenative Annulation Reaction

Abstract

The discovery of a direct method for the synthesis of three-ring heterocyclic carbazoles from unactivated arenes and anilides by a metal-free (organic) intermolecular dehydrogenative annulation reaction under ambient laboratory conditions is reported. Iodine(III) was used as the sole reagent either stoichiometrically from inexpensive phenyliodine diacetate or organocatalytically by in situ generation from PhI-mCPBA. In a single step, three C(sp)-H bonds and one N(sp)-H bond are functionalized from two different arenes for tandem C-C and C-N bond formation reactions.

An Intramolecular C(sp2)–H Amidation Using N‐Iodosuccinimide

“…In a continuation of our research interests towards controlling chemical reactions using weak interactions in nonprefunctionalized aromatic systems, in this paper we report an intramolecular C(sp 2 )–H amidation reaction (Figure c) for the synthesis of 1,2‐disubstituted benzimidazoles using NIS instead of a strong oxidant like phenyliodine diacetate (PIDA) . To date, numerous methods for the synthesis of N–H benzimidazoles have been established, but very few reports of the metal‐free direct synthesis of N ‐substituted benzimidazoles are known …”

“…Through the addition of the acid salt NaHSO 4 , the reactivity of the amine nitrogen towards iodine(III) was decreased by charge transfer. We have also recently shown that sulfonamide‐protected arylamines react in 2,2,2‐trifluoroethanol (TFE) to give carbazoles . Certain arylamines also reacted exothermically with PIDA.…”

“…The reaction time decreased dramatically to <30 min when the solvent was changed to the fluorinated solvent TFE at room temperature (Figure b) . We recently reported that reactions using hypervalent iodine regents gave the best results when carried out in fluorinated solvents . Various coupling reactions are known using I + reagents .…”

“…b) Control of the reactivity of amines in presence of phenyliodine diacetate (PIDA). For example, the usually explosive reaction of benzylamines and PIDA was controlled by the addition of NaHSO 4 , sulfonamides in fluorinated solvents led to carbazoles, styrene was difunctionalized through cation–π interactions . c) Dehydrogenative C(sp 2 )–H amidation using NIS (this work).…”

Iodine(III) Enabled Dehydrogenative Aryl C−S Coupling by in situ Generated Sulfenium Ion

“…[14] Many chemical reactions are well known to be controlled by weak interactions. [26] In continuation of our research focus towards the use of hypervalent iodine reagents in organic synthesis, [27] herein we report an intermolecular dehydrogenative aryl CÀS coupling reaction [28] for the synthesis of diaryl sulfides and aryl sulfinyl arenes (or diaryl sulfoxides) from the respective arenes and thiophenols via generation of sulfenium ion. Selective examples of the weak interactions like anionp, [16] cation-p, [17] charge-transfer, [18] halogen bonding, [19] hydrophobic effect, [20] etc.…”