Nilufa Khatun

Directing Group Assisted Copper-Catalyzed Chemoselective O-Aroylation of Phenols and Enols Using Alkylbenzenes

By using alkylbenzenes as aroyl surrogates, copper(II) catalyzed chemoselective O-aroylations of 1,3-dicarbonyl compounds and phenolic -OH ortho to carbonyl (-CHO, -COR) groups have been achieved. A dual mechanism operating in tandem for these transformations has been supported by a crossover experiment.

Generation of bis-Acyl Ketals from Esters and Benzyl Amines Under Oxidative Conditions

Treatment of benzylamines with esters at an elevated temperature are expected to give amides. However, in the presence of TBAI/TBHP, esters possessing a methylene carbon α-to oxygen with benzylamines provide bis-esters rather than the expected amides. Benzylamines under oxidative conditions generate less nucleophilic carboxylates, which couples at the sp(3) C-H bonds of esters and cyclic ethers to give bis-acyl ketals and α-acyloxy ethers, respectively.

Pd(II)-catalysed o-aroylation of directing arenes using terminal aryl alkenes and alkynes

A substrate-directed Pd-catalysed o-aroylation strategy has been demonstrated using new aroyl surrogates viz. terminal aryl alkenes and alkynes in the presence of TBHP. By a subtle change in catalyst from Cu to Pd, a differential selectivity is observed. While terminal aryl alkenes/alkynes in the presence of Cu/TBHP are reported to act as o-aryloxy (ArCOO–) sources, the use of Pd/TBHP installs an aroyl (ArCO–) group at the ortho position with respect to the directing arenes.

Palladium-Catalyzed Synthesis of 2-Aryl-2H-Benzotriazoles from Azoarenes and TMSN3.

Substrate-directed ortho C-H amination of azoarenes using TMSN3 as the source of nitrogen leading to the synthesis of 2-aryl-2H-benzotriazoles has been accomplished with the help of Pd/TBHP combinations. An intermolecular o-azidation (C-N bond formation) followed by an intramolecular N-N bond formation via nucleophilic attack of one of the azo nitrogen onto the o-azide nitrogen leads to cyclization with the expulsion of N2.

Divergent reactivities of o-haloanilides with CuO nanoparticles in water: a green synthesis of benzoxazoles and o-hydroxyanilides

In the present study, three divergent reaction paths emerged when o-haloanilides were subjected to CuO nanoparticles in water. o-Halo (I, Br) phenylbenzamides in the presence of CuO nanoparticles and Cs2CO3 in water at 100 °C provided o-hydroxyphenyl benzamides as the major product. However, a complete change in selectivity was observed in the presence of an organic base/ligand (TMEDA), giving 2-arylbenzoxazole as the exclusive product. The above selectivities were not clearly distinct when the corresponding alkylamides were treated either in the presence or absence of the ligand. A number of o-halophenyl alkylamides provided either exclusively o-dehalogenated products or a mixture of o-dehalogenated and o-hydroxylated products, but none gave 2-alkylbenzoxazoles. In addition to the above selectivities, the use of an environmentally friendly solvent (water) and base, and the recyclability of the catalyst make this procedure a benign alternative to the existing methods for the synthesis of these molecules, viz. o-hydroxybenzamides and o-arylbenzoxazoles.

Palladium catalyzed ortho-halogenation of 2-arylbenzothiazole and 2,3-diarylquinoxaline

A palladium catalysed ortho-halogenation strategy has been developed using benzothiazoles and quinoxalines as the directing substrates. This method provides mono-o-halogenated product at the other available ortho site of a mono-ortho substituted 2-arylbenzothiazole. However, ortho-unsubstituted 2-arylbenzothiazole afforded di-ortho halogenated product exclusively. The preformed (or installed) ortho-group is towards the sulphur side of the benzothiazole from energy minimised calculation. Thus the selective formation of di-ortho-halogenated products is due to favourable exposure of the second ortho site for subsequent halogenation. However the phenyl ring in 2,3-diarylquinoxalines can be selectively mono ortho halogenated. A plausible reaction mechanism has been proposed for this halogenation process.

CuO nanoparticle catalysed synthesis of 2H-indazoles under ligand free conditions

A CuO nano catalysed one-pot synthesis of 2H-indazoles has been devised from easily accessible starting materials viz. 2-bromobenzaldehydes, primary amines and sodium azide under ligand free conditions. The nano CuO catalyst played an important role during the formation of the intermolecular C–N bond followed by the intramolecular N–N bond, providing 2H-indazoles. This method has a broad substrate scope with a high tolerance of a variety of functional groups. The catalyst can be recycled up to three times, however with slight decreases in the yields each time.

A one-pot strategy for the synthesis of 2-aminobenzothiazole in water by copper catalysis

A straightforward, efficient and sustainable method for the synthesis of 2-aminobenzothiazoles has been achieved from in situ generated 2-halothioureas using copper(I) catalyst in water. The present study demonstrates that copper iodide (CuI) exhibits better efficiency in water towards intramolecular S-arylation compared to organic solvents. While (o-iodoaryl) thioureas are smoothly converted to the desired product in high yields with only catalytic quantity of CuI, addition of base and ligand are essential for bromo and chloro analogues. An unprecedented demethoxylation of o-methoxy-o-iodoarylthiourea and demethoxylation followed by a Friedel–Crafts type methylation (para to nitrogen) was observed in the aryl ring possessing the original methoxy group.

Benzylic ethers as arylcarboxy surrogates in substrate directed ortho C–H functionalisation catalysed by copper

A copper catalysed ortho-benzoxylation of 2-arylpyridines has been accomplished using benzylic ethers as the alternative arylcarboxy sources (ArCOO–) via sp2 C–H bond activation. The use of the Pd/TBHP catalytic system is reported to install an o-aroyl (ArCO–) moiety at the 2-arylpyridine while the Cu/TBHP combination fixes a benzoxy (ArCOO–) group at the ortho site.

A one pot synthesis of [1,3,4]-oxadiazoles mediated by molecular iodine

A one-pot synthesis of 3-amino-1,3,4-oxadiazoles has been achieved from the corresponding dithiocarbamate salt, employing the thiophilic property of molecular iodine. The precursor thiosemicarbazides could be derived in situ which underwent an intramolecular cyclodesulfurization in the presence of iodine to afford 3-amino-1,3,4-oxadiazoles exclusively. Apart from being milder and environmentally sustainable, this method involves a simple, reliable approach to give good to excellent yields of the desired products and is compatible with a wide range of functional groups.