Straightforward and highly efficient catalyst-free one-pot synthesis of dithiocarbamates under solvent-free conditions

[Structure: see text] A highly efficient and simple synthesis of dithiocarbamates is possible based on the one-pot reaction of amines, CS2, and alkyl halides without using a catalyst under solvent-free conditions. The mild reaction conditions, high yields, and broad scope of the reaction illustrate the good synthetic utility of this method. The reaction is a highly atom-economic process for production of S-alkyl thiocarbamates and successfully can be used in high quantities in the pharmaceutical or agrochemical industries.     

An expeditious and efficient synthesis of highly functionalized [1,6]-naphthyridines under catalyst-free conditions in aqueous medium

This is the first report of an innovative, one-pot, catalyst-free, pseudo-five-component synthesis of 1,2-dihydro[1,6]naphthyridines from methyl ketones, amines, and malononitrile in ecofriendly solvent water. The protocol avoids the use of expensive catalysts, toxic organic solvents and anhydrous condition. The approach to naphthyridines presented herein offers for the first time an unprecedented coupling which leads to the construction of both the nitrogen containing rings during the synthesis without starting from any nitrogen-containing heterocycle moiety.     

An efficient green synthesis of dispirohydroquinolines via a diastereoselective one-pot eight-component reaction

The one-pot eight-component reaction between Meldrum's acid, an aromatic aldehyde, and an aryl amine was achieved in the presence of citric acid catalyst. The corresponding dispirohydroquino-lines were obtained in good yields with excellent diastereoselectivity. This method is a combination of the Knoevenagel and Michael reactions.     

An efficient, microwave-assisted, one-pot synthesis of indoles under Sonogashira conditions

A microwave-assisted, one-pot, three-component coupling reaction for the synthesis of indoles has been developed. The reaction is carried out in two steps under standard Sonogashira coupling conditions from an N-substituted/N,N-disubstituted 2-iodoaniline and a terminal alkyne, followed by the addition of acetonitrile and an aryl iodide. A variety of polysubstituted indoles have been prepared in moderate to excellent yields using the present method.     

Polyethylene glycol (PEG-400) as an efficient and recyclable reaction medium for one-pot synthesis of polysubstituted pyrroles under catalyst-free conditions

Polyethylene glycol (PEG) was found to be an inexpensive non-toxic and effective medium for the one-pot synthesis of highly functionalized pyrroles. Utilizing this protocol various pyrrole derivatives were synthesized in excellent yields. Environmental acceptability, low cost, high yields, and recyclability of the PEG are the important features of this protocol.     

PEG-mediated catalyst-free expeditious synthesis of 2-substituted benzimidazoles and bis-benzimidazoles under solvent-less conditions

A wide variety of 2-substituted benzimidazoles and bis-benzimidazoles were synthesized in high yields by PEG-mediated catalyst-free synthesis under solvent-less conditions. The products were directly recrystallized from hot methanol. The reaction occurred giving excellent yields with low as well as high molecular weight PEGs.     

Water-mediated,green, and efficient synthesis of bisquinolones under catalyst-free conditions

Water-mediated, green, and efficient synthesis involving condensation of 4-hydroxy-1-methylquinoline-2(1H)-one (3) with different aromatic and heterocyclic aldehydes (4a–n) leading to 3,3′-(arylmethylene)-bis-(4-hydroxy-1-methylquinolin-2(1H)-one) 5(a–n) under catalyst-free conditions is described. This reaction has an easy workup without using column chromatography and provides excellent yields of the products in shorter reaction times. It does not require any catalyst and uses water as the medium which is the greenest solvent. 3 required in this work was itself obtained by condensation of N-methylaniline (1) with malonic acid (2) in the presence of POCl₃ using a previously reported procedure.     

Solar radiation-assisted one-pot synthesis of 3-alkylated indoles under catalyst-free conditions

Solar radiation-assisted green approach was developed for the chemoselective synthesis of 3-alkylated indoles via Yonemitsu-type condensation under catalyst-free conditions. The desired products were formed by one-pot three-component reaction of indole, aromatic aldehydes, and β-dicarbonyl compounds in polyethylene glycol-400 (PEG-400). The scope and generality of the presented approach were extended by various aromatic aldehydes and CH activated compounds. Using non-volatile solvent and renewable energy resources, absence of any catalyst, energy conservation, and the selective production of heterodimer product instead of homodimer adducts such as bisindole or xanthine, increase the economic and environmental effectiveness of the present protocol.     

An efficient green synthesis of proline-based cyclic dipeptides under water-mediated catalyst-free conditions

l-Proline-based cyclic dipeptides were synthesized from N-Boc-protected dipeptide methyl esters under catalyst-free condition using water as a solvent. One-pot deprotection and cyclization have been used as the key steps, providing an efficient and environmentally friendly approach. Clean reaction conditions, easy isolation, and good yields of cyclic dipeptides are the salient features of the proposed methodology.     

Novel one-pot expeditious synthesis of 2,4-disubstituted thiazoles through a three-component reaction under solvent free conditions

An expeditious one pot method has been developed for the synthesis of 2,4-disubstituted thiazoles under solvent free conditions via a multicomponent approach. Substituted thiazoles were synthesized with high yields by the reaction of cyclic ketones, thiosemicarbazide, and phenacyl bromides or 3-(2-bromoacetyl)-2H-chromen-2-ones in a shorter reaction time with high purity via simple purification technique.     

Solvent-and catalyst-free synthesis of dihydropyrimidinthiones in one-pot under focused microwave irradiation conditions

Fifteen dihydropyrimidinthiones have been synthesized by microwave-assisted Biginelli reactions without any solvent or catalyst. The advantages of this novel protocol include the excellent yield, operational simplicity, short time and the avoidance of the use of organic solvents and catalysts.     

An expeditious and one-pot synthesis of unsymmetrical 2,5-disubstituted-1,3,4-oxadiazoles under microwave irradiation and solvent-free conditions

A one-pot synthesis of some unsymmetrical 2,5-disubstituted-1,3,4-oxadiazoles via cyclocondensation of benzoylhydrazines with orthoesters under solvent-free and microwave conditions are described here. The reaction is efficiently catalyzed by silica- supported sulfuric acid as it provided the title compounds in high yields and relatively short times. The catalyst is reusable and can be applied several times without considerable decrease in the yields and rates of the reactions.     

Highly efficient and catalyst-free synthesis of unsymmetrical thioureas under solvent-free conditions

A highly efficient and simple synthesis of unsymmetrical thioureas is reported based on the reaction of readily synthesized dithiocarbamates with amines, without using any catalyst under solvent-free conditions. The short reaction time, high yields, and solvent-free conditions are advantages of this method. We did not observe the formation of any symmetric disubstituted thiourea, under these reaction conditions.     

An efficient one-pot, two-step synthesis of 4-substituted 1-heteroarylpiperazines under microwave irradiation conditions

A highly efficient one-pot, two-step microwave procedure has been developed for the synthesis of 4-substituted 1-heteroarylpiperazines. Microwave heating of heteroaryl chlorides with 1,4-diazabicyclo[2.2.2]octane (DABCO) at 160 °C for 15 min yielded 1-heteroaryl-4-(2-chloroethyl)piperazines, which could be further reacted with various nucleophiles, again under microwave irradiation conditions, to give an array of 4-substituted 1-heteroarylpiperazines in good to excellent yields.     

Three-component one-pot synthesis of pyrazino[2,3-a]acridine derivatives under catalyst-free conditions

A new series of pyrazino[2,3-a]acridine derivatives were prepared, via three-component reaction of quinoxalin-6-amine, aromatic aldehydes and 5,5-dimethyl cyclohexane-1,3-dione or cyclohexane-1,3-dione in ethanol as a solvent at reflux. The advantages of this protocol include mild reaction conditions, easy purification, high yields, and catalyst-free approach.     

A new diastereoselective multicomponent, one-pot strategy for the synthesis of 3-substituted isoindolinones via efficient C-C bond formation

A new three-component reaction among o-phthalaldehyde, N-alkyl/aryl substituted urea, and an aromatic aldehyde has been developed at ambient condition, and a class of isoindolinones with novel C-3 substitution were conveniently synthesized. The general diastereomeric excess as high as over 99% of the products indicated the excellent stereoselectivity posed in this multicomponent reaction.     

An efficient one-pot,multi-component diastereoselective synthesis of functionalized cyclopenta[c]chromenes

A novel one-pot, multi-component diastereoselective synthesis of functionalized cyclopenta[c]chromenes is described. This transformation proceeds via a Michael addition-cyclization reaction sequence between trialkyl phosphites, dialkyl acetylenedicarboxylates and in situ generated 2-(1-(2-oxo-2H-chromen-3-yl)alkylidene)malononitriles from the condensation of 3-acyl-2H-chromen-2-ones and malononitrile.