Saikat Maiti

IBX works efficiently under solvent free conditions in ball milling

IBX (2-iodoxybenzoic acid), discovered in 1893, is an oxidant in synthetic chemistry whose extensive use is impeded by its explosiveness at high temperature and poor solubility in common organic solvents except DMSO. Since the discovery of Dess–Martin Periodinane in 1983, several modified IBX systems have been reported. However, under ball milling conditions, IBX works efficiently with various organic functionalities at ambient temperature under solvent free conditions. Also, the waste IBA (2-iodosobenzoic acid) produced from the reactions was in situ oxidized to IBX in the following step using oxone and thus reused for multiple cycles by conserving its efficiency (only ∼6% loss after 15 cycles). This work describes an overview of a highly economical synthetic methodology which overcomes the problems of using IBX, efficiently in gram scale and in a non-explosive way.

An Organic Intermolecular Dehydrogenative Annulation Reaction

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(sp2)-H bonds and one N(sp3)-H bond are functionalized from two different arenes for tandem C-C and C-N bond formation reactions.

Dehydrogenative Aromatic Ring Fusion for Carbazole Synthesis via C–C/C–N Bond Formation and Alkyl Migration

An intermolecular dehydrogenative annulation (IDA) for carbazole synthesis via sequential C-C/C-N bond formation with a selective alkyl group migration is reported. Using the hypervalent iodine(III) reagent PhI(OAc)2 (PIDA), in a one-pot operation, up to five C(sp2)-H bonds, one N(sp3)-H bond functionalization, and one alkyl (Me, Et) group migration could all be achieved from non-prefunctionalized 1,3,5-trialkylbenzenes and anilides under ambient laboratory conditions. Mechanistically, it is shown that PIDA reacts with anilides to generate a nitrenium ion or an equivalent carbenium ion which influences the second aromatic ring to be activated for C-C/C-N bond formation. Strategically, regioselective fusion of arenes to anilides is described.

Electron-Rich Aromatics Under Ball Milling: Oxidative Aryl-iodination Using I2-Oxone and Biarylation with I2

Abstract We report here a simple, efficient, and environmentally friendly methodology for electrophilic aryl-iodination of electron-rich arenes using I2-oxone under ball milling. The reactions work efficiently under solvent-free conditions at room temperature. We have also shown that iodine could be used as catalyst for metal-free biaryl coupling of a few electron-rich substrates. In addition, one-pot multistep synthesis has been demonstrated for one substrate. GRAPHICAL ABSTRACT

Soft–Hard Acid/Base-Controlled, Oxidative, N-Selective Arylation of Sulfonanilides via a Nitrenium Ion

In iodine(III)-catalyzed, dehydrogenative arylations of sulfonanilides, the functionalization of C-C bonds is preferred over the functionalization of C-N bonds. Herein, an unprecedented N-selective arylation of sulfonanilides using soft-hard acid-base (SHAB) control by a nitrenium ion over a carbenium ion is reported. Treatment of sulfonanilides with iodine(III) led to the formation of nitrenium ions (soft), which preferentially react with biphenyls (soft) over bimesityl (hard) to generate C-N bonds. The iodine(III) was generated in situ by using PhI and mCPBA at room temperature.

Oxidative N-Arylation for Carbazole Synthesis by C–C Bond Activation

Activation of strong C-C σ-bonds is quite challenging. We report here an intramolecular oxidative N-arylation method of biarylsulfonamides via cleavage of C-C bonds toward synthesis of heterocycle carbazoles. The stability of generated carbocations could control the reactivity of a nitrenium ion for the C-N bond formations at the ipso-carbon via a retro-Friedel-Crafts-type reaction using hypervalent iodine(III) reagent PhI(OAc)2.

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

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.

The mechanochemical synthesis of quinazolin-4(3H)-ones by controlling the reactivity of IBX

Performing any synthesis using several arylamines and hypervalent iodine(V) reagents by direct mixing is unrealistic because of the high exothermic reaction or explosion. Herein we demonstrate, when anilines were substituted with an amide group at the ortho-position, successful chemical reactions could be performed due to intramolecular control. At maximum contact of the reacting substances, i.e., under solvent-free mechanochemical conditions, 2-aminobenzamides, aryl-, alkylaldehydes and the iodine(V) reagent o-iodoxybenzoic acid (IBX) led to substituted quinazolin-4(3H)-one derivatives in fair yields.