Nemai C. Ganguly

CERIUM(IV) AMMONIUM NITRATE MEDIATED NITRATION OF COUMARINS

A new convenient method of nitration of coumarins using cerium(IV) ammonium nitrate (CAN) has been developed. Higher regioselectivity is observed with CAN and hydrogen peroxide in aqueous medium in comparison with CAN in acetic acid for nitration of 7-hydroxycoumarin, 7-hydroxy-4-methyl coumarin and their derivatives.

Studies on Regioselectivity of Nitration of Coumarins with Cerium(IV) Ammonium Nitrate: Solid-State Nitration of 6-Hydroxy-Coumarins on Montmorillonite K-10 Clay Support Under Microwave Irradiation

Abstract 6-Hydroxycoumarins and their O-methyl ethers were selectively nitrated in the carbocyclic ring even in the presence of activating 4-Me group in the 2-pyrone ring with cerium(IV) ammonium nitrate (CAN) in acetic acid and acetonitrile in acceptable-to-excellent yields. Acetonitrile was found to be a better solvent for regioselective nitration than acetic acid. Use of CAN on montmorillonite K-10 clay under microwave irradiation for expeditious solvent-free regioselective nitration has been revealed for the first time.

Ligand-free copper-catalyzed efficient one-pot access of benzo[b]pyrido[3,2-f][1,4]oxazepinones through O-heteroarylation-Smiles rearrangement-cyclization cascade

Efficient synthesis of a library of novel benzopyrido[1,4]oxazepinones was accomplished by Cs2CO3-mediated one-pot coupling of N-substituted-o-chloronicotinamides and o-halogenated phenols using cuprous oxide catalysis in DMF at 120 °C through an O-heteroarylation-Smiles rearrangement-cyclization cascade (16 examples). The C–N bond construction process is biased in favour of Smiles rearrangement allowing regioselective generation of these tricyclic molecular architectures essentially free from Goldberg-N-arylation products in good to excellent yields.

OXIDATIVE DEPROTECTION OF OXIMES USING PYRIDINIUM FLUOROCHROMATE AND HYDROGEN PEROXIDE

A simple convenient procedure of oxidative deoximation has been developed using pyridinium fluorochromate (PFC), in combination with 30% hydrogen peroxide. The method has been found to be effective for a wide range of aliphatic and aromatic oximes, and may be used for selective cleavage of aldoximes in the presence of ketoximes.

Sodium Perborate Tetrahydrate–Mediated Transformations of 2′-Hydroxychalcones to Flavanones, Flavones, and 3′, 5′-Diiodoflavone Under Mild, Environmentally Friendly Conditions

Abstract Sodium perborate tetrahydrate has been utilized as a nucleophilic catalyst for facile conversion of 2′-hydroxychalcones to flavanones in warm aqueous acetonitrile, and then these chalcones, upon oxidative cyclization in warm acetic acid with an excess of the same reagent, afforded flavones in acceptable yields. One-pot synthesis of 3′,5′-diiodoflavone has been accomplished by diacetoxyiodobenzene-catalyzed iodination of 2′-hydroxychalcone with tetra-n-butylammonium iodide in acetic acid in the presence of sodium perborate as a terminal oxidant. GRAPHICAL ABSTRACT

Iodine in aqueous micellar environment: a mild effective ecofriendly catalytic system for expedient synthesis of bis(indolyl)methanes and 3-substituted indolyl ketones

The three-component condensation reaction of indoles with carbonyl compounds to yield bis(indolyl)methanes has been accomplished with a catalytic amount of iodine (2 mol%) in the presence of sodium dodecylsulfate (SDS) in aqueous solution above its critical micellar concentration (cmc). The surfactant-aided water-compatible Lewis acid catalyst has been found to be efficient for a wide range of carbonyl compounds including aromatic aldehydes bearing electron-releasing and electron-withdrawing groups, α,β-unsaturated aldehydes, heterocyclic aldehydes, cyclic and aromatic ketones with respect to yield, and reaction time. The protocol has been extended to Michael addition of indoles with α,β-unsaturated ketones exclusively yielding 3-substituted indolyl ketones in excellent yields.

PYRIDINIUM FLUOROCHROMATE SUPPORTED ON WET ALUMINA: A MILD CONVENIENT REAGENT FOR THE FACILE DEPROTECTION OF ALDOXIMES

ABSTRACT A simple mild method of oxidative deoximation based on pyridinium fluorochromate (PFC) on wet alumina support is described. This method is particularly effective for rapid deprotection of aldoximes and aliphatic ketoximes. Sterically hindered ketoximes are resistant to the reagent.

Convenient, Mild Catalytic Deprotection of Oximes to Carbonyl Compounds with Hydrogen Peroxide and Iodine Catalyst in Aqueous Acetonitrile

Abstract A clean, mild, and efficient catalytic deoximation procedure compatible with several common functional groups has been developed using 30% hydrogen peroxide activated by iodine catalyst in aqueous acetonitrile under essentially neutral conditions. The mechanistic features of an iodonium ion–driven nucleophilic cleavage of oximic C˭N have been revealed.

Boric Acid–Catalyzed One-Pot Access to 7-Aryl-benzopyrano[4,3-b] benzopyran-6,8-diones Under Aqueous Micellar Conditions

Abstract A mild protocol for the synthesis of 7-arylbenzopyrano[4,3-b]benzopyran-6,8-diones by three-component reaction of 4-hydroxycoumarin, aromatic aldehyde, and 5,5-dimethylcyclohexane-1,3-dione (dimedone) with boric acid catalyst under aqueous micellar conditions is described. Good to excellent yield, high selectivity, tolerance of several common functional and protecting groups, and green features including avoidance of organic solvent in the reaction as well as isolation stage and use of nontoxic water-compatible mild Lewis acid catalyst are key attractive features of the protocol. [Supplementary materials are available for this article. Go to the publishers online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.] GRAPHICAL ABSTRACT

Mild, Efficient, and Greener Dethioacetalization Protocol Using 30% Hydrogen Peroxide in Catalytic Combination with Ammonium Iodide

Abstract A simple, mild, efficient, and expedient greener dethioacetalization protocol employing a catalytic amount of nontoxic ammonium iodide (10 mol%) in combination with 30% hydrogen peroxide as terminal oxidizer is revealed. The reagent accomplished facile deprotection of 1,3-dithianes and dithiolanes of activated aromatic substrates in an aqueous medium in the presence of sodium dodecylsulfate (SDS) at room temperature under virtually neutral conditions. Deactivated and sterically encumbered substrates, which are otherwise reluctant to cleave under aqueous micellar conditions, were expeditiously cleaved in good to excellent yields in acetic acid. The method is tolerant, with several acid-sensitive protecting groups, such as tert-butyldiphenylsilyl (TBDPS) ether, aryl acetate, NHBoc, and NHBn, and with further oxidation of oxidation-prone activated benzaldehydes and furyl aldehydes. A tentative mechanism of hypoiodous acid–mediated catalytic cleavage is proposed.