I. R. Siddiqui

Tandem imino-pinacol coupling-aza-Michael reaction promoted by Zn/InCl3: a novel multicomponent strategy for diastereoselective synthesis of monocyclic 1,4-diazepine in water

Aldimine formed in situ on bimolecular reductive coupling in the presence of zinc and accelerated by indium(III) chloride in water afforded N,N′-diphenyl-1,2-diaryl-1,2-diamino ethane which on aza-Michael addition with α,β-unsaturated ketone and subsequent dehydrative cycloaddition yielded monocyclic 1,4-diazepine in excellent yield and with high diastereoselectivity in one-pot. The whole reaction sequence proceeded smoothly with quantitative conversion of reactants into product. The reaction pathway was supported by isolation of N,N′-diphenyl-1,2-diaryl-1,2-diamino ethane and its conversion into product by reaction with α,β-unsaturated ketone under similar reaction conditions.

Electrosynthesis and screening of novel 1,3,4-oxadiazoles as potent and selective antifungal agents

The electrochemical oxidation of aldehyde-N-aroylhydrazone has been studied in the presence of NaClO4 as supporting electrolyte in MeOH solution using cyclic voltammetry and controlled potential electrolysis. The results indicate that intramolecular cyclization of aldehyde-N-aroylhydrazone has been successfully performed at a platinum electrode in an undivided cell with good yields of the corresponding 1,3,4-oxadiazoles at ambient conditions. The reaction products were characterized by spectroscopic methods and a mechanism was deduced from voltammetry studies. The antifungal activity of the synthesized compounds was evaluated on Fusarium oxysporum, Alternaria solani, Candida albicans and Aspergillus niger. The results revealed that all the synthesized compounds have significant antifungal activity against the tested fungi. Among the synthesized derivatives 7b, 7d, 7g, 7h, 7i, 7j and 7r were found to be the most effective antifungal compounds.

Ionic liquid promoted spiroannulation via hetero-Michael addition and intramolecular heterocyclisation

A sequential efficient method for the synthesis of novel spiro-5-thiazolidin-2-one-indolo[1,5]benzothiazepine from readily available isatin, 4-thioxothiazolidin-2-one and 2-aminothiophenol is reported. The synthesis involves formation of N-methyl-3-(2-oxo-4-thioxothiazolidinon-5-ylidene)-1,3-dihydro indol-2-one by [bmIm]OH promoted Knoevenagel condensation of 4-thioxo-2-thiazolidinone with isatin. The Knoevenagel product on ionic liquid promoted thia-Michael addition with 2-aminothiophenol and intramolecular cyclocondensation yielded the title compounds with high atom economy. The ionic liquid, [bmIm]OH was recovered completely and recycled thrice for the synthesis with no appreciable decrease in the efficiency of the process. The whole sequence of reactions proceeded with quantitative transformation of reactants into spiro [1,5]benzothiazepine at ambient temperature. The sequential reaction pathway is supported by the isolation of the thia-Michael adduct of the knoevenagel product with 2-aminothiophenol and quantitative conversion of the adduct into the final products under the same reaction conditions.

Synthesis of fused pyridines in the presence of thiamine hydrochloride as an efficient and reusable catalyst in aqueous conditions

Efficient and straightforward synthesis of fused pyridine derivatives was achieved from electron-rich amino heterocycles and Knoevenagel products derived from aldehyde and malononitrile under aqueous media at 90 °C in the presence of thiamine hydrochloride as a reusable, green catalyst. The strategy in this protocol involves addition on an activated olefinic bond formed in situ by Knoevenagel condensation between an aromatic aldehyde and an active methylene compound. The Michael product on subsequent cyclo condensation yielded fused pyridine in high yield. It offers several advantages such as inexpensive, easily available and recyclable catalyst, simple operational procedure, excellent yield and use of aqueous medium that is considered to be relatively eco-friendly. Vitamin B1 was recovered and reused thrice.

Chitosan: an efficient promoter for the synthesis of 2-aminopyrimidine-5-carbonitrile derivatives in solvent free conditions

Reusable chitosan without any post-modification, with active –NH2 and –OH groups, was found to be a highly efficient and renewable heterogeneous catalyst for the rapid and convenient synthesis of 2-aminopyrimidine-5-carbonitrile derivatives from guanidines, aldehydes and cyanoketones, under mild reaction conditions at 85 °C in good yields. Undoubtedly this methodology gives a facile and straightforward pathway to construct 2-aminopyrimidine-5-carbonitrile derivatives in an eco-friendly fashion.

Mineral Supported Facile Synthesis of Novel 4-Hydroxybenzoxazin-2-Thione N-Nucleosides

One-pot montmorillonite K-10 clay-supported reactions of substituted/unsubstituted salicylaldehyde and ribosyl/deoxyribosyl thioureas expeditiously yielded novel N-nucleosides, 4-hydroxy-3,4-dihydro-3-(β-D-ribofuranosyl or β-D-2 ′-deoxyribofuranosyl)-2 ″-benz[e]-1,3-oxazin-2-thione via cycloisomerization of aldehyde intermediate under solvent-free microwave irradiation conditions.

Molecular iodine catalysed domino cyclization in aqueous medium: a simple and efficient synthetic route to 1,4-dihydropyridazines

A facile, efficient and environmentally friendly approach has been developed for the diverse synthesis of 1,4-dihydropyridazines from (E)-2-benzylidene-1-phenylhydrazine and α,β-unsaturated aldehyde under aqueous condition using molecular iodine as a green and recoverable catalyst. This procedure features low cost and easily available starting materials, an inexpensive and recoverable catalyst, short reaction time, reliable scalability, excellent yield and mild reaction conditions, as well as use of aqueous medium. The scope of this method was thoroughly explored under three different reaction conditions resulting in the generation of a library of title compounds. In view of the various advantages of the present investigation, this methodology gives a convenient and straightforward pathway to construct 1,4-dihydropyridazines in an eco-friendly fashion.

Diastereoselective synthesis of furopyranopyridine in ionic liquid/water without additional catalyst

3,5-Diarylidene-1-methyl-piperidin-4-one derived in situ from N-methylpiperidinone and benzaldehyde undergoes intermolecular [4 + 2] hetero-Diels–Alder reactions with 2,3-dihydrofuran in [bmim]BF4–H2O (1 : 1) to afford furopyranopyridine derivatives in high to quantitative yields. Heterodienes, 3,5-diaryldiene-1-methylpiperidin-4-one an electron deficient oxadiene added to 2,3-dihydrofuran an electron rich dienophile because of an inverse electron demand, yielding furopyranopyridines with a high atom economy.

Three-component solvent-free diastereoselective formation of oxo-thiazolidinylthiazoles under microwave irradiation

The one-pot diastereoselective cyclisation of 4,4′-bis(2″-aminothiazol-4″-yl)bibenzyl to 4,4′-bis[2″-(2″′-aryl-5″′-methyl/carboxymethyl-4″′-thiazolidinon-3″′-yl)thiazol-4″-yl]bibenzyls, in high yields (85-96%) under the influence of microwave radiation, is described.

Electrochemical oxidation of aldehyde- N -arylhydrazones into symmetrical-2,5-disubstituted-1,3,4-oxadiazoles

A convenient, efficient and one-pot synthesis of chemically and pharmaceutically interesting symmetrical-2,5-disubstituted-1,3,4-oxadiazoles is reported. The protocol involves anodic oxidation of aldehyde-N-arylhydrazones in anhyd. MeCN–LiClO4. Constant potential electrolysis carried out in an undivided cell and platinum electrodes leads to the formation of the corresponding oxadiazoles under ambient condition and the mechanism was deduced from voltammetry studies. The reaction proceeded smoothly with high atom economy.