Dipak S. Dalal

β-Cyclodextrin-mediated highly efficient [2+3] cycloaddition reactions for the synthesis of 5-substituted 1H-tetrazoles

A β-cyclodextrin-promoted [2+3] cycloaddition reaction between nitriles and sodium azide in the presence of ammonium chloride in DMF at 120 °C is reported, affording various 5-substituted 1H-tetrazoles in good to excellent yields in short reaction times. The presence of β-CD renders the formation of a precipitate-like gel in the reaction media when heated. No precipitation occurs in the absence of NaN3 and NH4Cl. The precipitation responses with other salts such as LiCl and NiCl2 were weaker than with NH4Cl. In the present paper the application of supramolecular aggregates is reported for the [2+3] cycloaddition reaction. β-Cyclodextrin can be recovered and reused without any significant loss of activity.

An efficient synthesis of 3-indolyl-3-hydroxy oxindoles and 3,3-di(indolyl)indolin-2-ones catalyzed by sulfonated β-CD as a supramolecular catalyst in water

Abstract Sulfonated-β-cyclodextrin (β-CD-SO3H) promoted efficient and fast electrophilic substitution reaction of indoles with various isatins reflux in water is reported affording various 3-indolyl-3-hydroxy oxindoles and 3,3-di(indolyl)indolin-2-ones in good to excellent yields in short reaction time.

Fly‐Ash‐Supported Synthesis of 2‐Mercaptobenzothiazole Derivatives under Microwave Irradiation

Abstract Microwave‐assisted, solvent‐free alkylation and acylation of 2‐mercaptobenzothiazole has been attempted using silica gel, alumina, and a new solid support, fly ash. Fly ash, a waste generated at thermal power stations, could be used as solid support just as efficiently as commercial supports. The additional features of methodology include a much faster reaction, easy workup, higher yields, higher purity of the products, and an ecofriendly approach.

Highly selective fluorimetric sensor for Cu2+ and Hg2+ using a benzothiazole-based receptor in semi-aqueous media and molecular docking studies

A new chemosensor (Z)-ethyl 2-((Z)-2-(benzo[d]thiazol-2-ylimino)-4-oxo-3-phenylthiazolidin-5-ylidene)acetate (receptor 1) was designed and synthesized under catalyst-free conditions. Receptor 1 was characterized by various spectroscopic techniques and its structure was solved by single-crystal X-ray diffraction. Receptor 1 was shown to be based on an internal charge transfer mechanism with the benzothiazole unit. These results were complemented by density functional theory calculations. The fluorescent emission of receptor 1 in CH3OH/H2O (50:50 v/v) was significantly quenched in the presence of Cu2+ and Hg2+, but not in the presence of other tested metal ions. Receptor 1 formed complexes in a 1:1 stoichiometry with Cu2+ and Hg2+ and the detection limits were 0.36 and 2.49 μM, respectively. In addition to the sensing study, the nature of the interactions of 1 with aldose reductase inhibitor was investigated using molecular docking studies.

Inclusion complex of Isatoic anhydride with β-cyclodextrin and supramolecular one-pot synthesis of 2, 3-dihydroquinazolin-4(1H)-ones in aqueous media

The inclusion complex of isatoic anhydride with β-cyclodextrin was formed as a result of intermolecular interaction between isatoic anhydride with β-CD. The inclusion complex was confirmed by IR spectroscopy, X-ray diffraction and DSC studies. From application of complex, herein we have described a simple and efficient protocol for synthesis of 2, 3-dihydroquinazoline-4(1H)-one derivatives by one pot condensation of isatoic anhydride, ammonium acetate or amine and aldehyde using β-CD as a supramolecular catalyst in aqueous media.

Bovine serum albumin catalyzed one-pot, three-component synthesis of dihydropyrano[2,3-c]pyrazole derivatives in aqueous ethanol

Bovine serum albumin (BSA) catalyzed synthesis of dihydropyrano[2,3-c]pyrazole derivatives via a one pot, three component reaction of an aldehyde/ketone/isatin, malononitrile and 3-methyl-1H-pyrazol-5-(4H)-one in H2O–EtOH (7 : 3) at ambient temperature was developed in this work. The catalyst was found to work efficiently for aldehydes, ketones and isatins to give the corresponding dihydropyrano[2,3-c]pyrazole and spiro[indoline-3,4′-pyrano[2,3-c]pyrazole] derivatives in high yields. BSA showed a broad range of catalytic promiscuity towards various aldehydes, aromatic/aliphatic ketones and substituted isatins. The use of an environmentally benign protocol, reusability of the catalyst, avoidance of hazardous solvents, excellent yields, easy work up and no byproduct formation make BSA an attractive candidate for further applications as a biocatalyst.

Ammonium acetate mediated synthesis of 5-substituted 1H-tetrazoles

Synthesis of 5-substituted 1H-tetrazoles was achieved by [3+2] cycloaddition of nitriles and sodium azide in the presence of ammonium acetate. The reaction proceeds in situ formation of ammonium azide. Present protocol has advantage of good to excellent yields, short reaction times and simple isolation of products than reported methods.

Green Process Development for the Synthesis of Aliphatic Symmetrical N,N′-Disubstituted Thiourea Derivatives in Aqueous Medium

Abstract A highly efficient green process for the synthesis of N,N′-disubstituted aliphatic thiourea derivatives using primary aliphatic amines and carbon disulfide in aqueous medium at room temperature via a nonisothiocyanate route is described. This protocol illustrates the rapid preparation of N,N′-disubstituted aliphatic thiourea derivatives in excellent yields with some advantages such as no catalyst and simple workup without any side product formation. Moreover the new route is concise, chromatography-free, and adaptable to pilot-scale preparation. GRAPHICAL ABSTRACT

Solid-Supported Synthesis of Bio-active Carvacrol Compounds Using Microwaves

Abstract The most abundant and potent natural products having a broad spectrum of biological activity against various pests are terpenoids, especially monoterpenoids. The chemical modification of natural monoterpenoids has been reported to result in modified biological activity. The present work emphasizes the structural modification of carvacrol, a phenolic monoterpenoid, through the synthesis of different ether and ester derivatives that are useful for structure–activity relationship studies to exploit the potent molecules. The carvacrol was reacted with alkyl halides and acid chlorides under microwaves using solid supports such as silica gel, alumina, and fly ash to give ethers and esters, respectively. The synthesis of dimeric ether and ester compounds using dihalides and acid dichlorides was conducted with novel reactions. Additional features of the methodology include very fast reactions, higher yields and purities of the products, and an ecofriendly approach.

Simple and Efficient Synthesis of 5-Substituted-3-phenyl-2-thioxoimidazolidin-4-one Derivatives from S-Amino Acids and Phenylisothiocyanate in Et3N/DMF-H2O

Abstract A concise approach for the transformation of various S-amino acids into the 5-alkyl-3-phenyl-2-thioxoimidazolidin-4-one heterocycles using phenylisothiocyanate is described. Phenylthiohydantoins of amino acid were synthesized at room temperature in Et3N/DMF-H2O with easy workup and excellent yields. GRAPHICAL ABSTRACT