Synthesis of sulfides under solvent- and catalyst-free conditions

Abstract  A simple, highly efficient, and green protocol has been developed for preparation of sulfides from alkyl or aryl thiols and benzyl-, allyl-, t-butyl, and adamantyl halides under solvent- and catalyst-free conditions. Graphical abstract        

Ultrasound-irradiated Michael addition of amines to ferrocenylenones under solvent-free and catalyst-free conditions at room temperature

A facile Michael addition of ferrocenylenones with aliphatic amines under ultrasound irradiation in the absence of solvent and catalyst at room temperature can afford 1-ferrocenyl-3-amino carbonyl compounds rapidly in high yields, which is also efficient in the aza-Michael reaction of other α,β-unsaturated carbonyl compounds such as chalcone, carboxylic ester, etc. However, aromatic amines do not undergo the conjugate addition at all, and the reactions under existing methods do not proceed or take place in low yield after a long reaction time. Apart from experimental simplicity, generality and selectivity, the advantages of this methodology are the rapid, environmentally benign and less expensive processes, which will contribute to the progress of green chemistry.     

Formylation without catalyst and solvent at 80 °C

A simple and efficient protocol for N-formylation of aliphatic and heterocyclic amines has been described with formic acid in the absence of catalyst and solvent.     

Visible light irradiation promoted catalyst-free and solvent-free synthesis of pyrano[2,3-d]pyrimidine scaffolds at room temperature

A catalyst-free and solvent-free synthetic route for convenient one-pot synthesizing pyrano[2,3-d] pyrimidine scaffolds through Knoevenagel-Michael cyclocondensation is reported using visible light irradiation as a green promoter at room temperature based on green chemistry principles. Completing the reactions takes thoroughly less time while obtaining the products in outstanding yields. This green method includes the application of non-hazardous reaction circumstances, direct work-up without column chromatographic separation, catalyst-free, solvent-free, cost effective, simple synthesis, one-pot procedure, and high atom-economy.     

Facile N-formylation of amines using Lewis acids as novel catalysts

Alky, aryl, and heteroaryl amines were found to react efficiently with formic acid under Lewis acid catalysis giving N-formyl derivatives in high yields. A study of ZnCl₂-catalyzed N-formylation of a variety of amines using formic acid as formylating agent is described.     

Solvent-free and catalyst-free method for the synthesis of 2,4,5-triarylimidazoles under microwave irradiation

A facile procedure for the synthesis of 2,4,5-triarylimidazoles is being reported starting from benzil, aromatic aldehyde and ammonium acetate. The reactions were carried out with catalyst-free, solvent-free and under microwave irradiation conditions in high yield (80–99%) with short time (3–5 min) and environmental benign, as well as convenient operation. The structures of the compounds have been confirmed on the basis of their IR, ¹H NMR, and/or ¹³C NMR, MS, and elemental analyzer.     

A catalyst-free N-benzyloxycarbonylation of amines in aqueous micellar media at room temperature

N-Benzyloxycarbonylation of amines was carried out in aqueous micellar media. Aliphatic (open and cyclic), aromatic and heteroaromatic amines react with Cbz-Cl to give excellent yields of products. The reactions were carried out in water and at room temperature.     

A very simple and highly efficient procedure for N-formylation of primary and secondary amines at room temperature under solvent-free conditions

N-Formylation of primary and secondary amines has efficiently been carried out at room temperature in excellent yields by using catalytic amount of sodium formate in formic acid under solvent-free conditions. The process is remarkably simple and environmentally benign.     

An efficient and chemoselective Cbz-protection of amines using silica-sulfuric acid at room temperature

A simple, facile, and chemoselective N-benzyloxycarbonylation of amines using silica-sulfuric acid that proceeds under solvent-free conditions at room temperature has been achieved. These reactions are applicable to a wide variety of primary (aliphatic and cyclic) secondary amines, amino alcohols, and heterocyclic amines.     

A green protocol for the N-formylation of amines using molybdate sulfuric acid as a reusable solid catalyst

A novel and efficient method for the N-formylation of amines via the reaction of orthoformates and amines is developed. The reactions are mediated by a catalytic amount of molybdate sulfuric acid as a heterogeneous solid acid.     

An efficient method for the N-formylation of amines under catalyst- and additive-free conditions

A simple catalyst- and additive-free method for the N-formylation of amines has been developed. The advantages of this protocol include a wide range of functional group tolerance, high efficiency and a lack of required extra promoters under mild conditions. This convenient strategy will provide a facile synthesis towards N-formamide natural products and pharmaceutical derivatives. A mechanism that involves difluorocarbene is proposed for this reaction.     

Transformation of aldehydes or alcohols to amides at room temperature under aqueous conditions

A novel and efficient method for the synthesis of amide has been developed. The reactions proceeded smoothly under aqueous conditions at room temperature and generated the corresponding products in good to excellent yields. It is worth noting that alkyl amines which did not react in known approaches are well tolerated in our system.     

Catalyst-free and solvent-free method for the synthesis of quinoxalines under microwave irradiation

A facile procedure for the synthesis.of quinoxalines is being reported starting from benzil and 1,2-diaminobenzene. Thereactions were carried out catalyst-free, solvent-free and under microwave irradiation conditions in high yield (84-98%) with short time (3-6 rain) and environmental benign, as well as convenient operation. The structures of all the compounds have been confirmed on the basis of their IR, 1H NMR, and/or 13C NMR, mass spectral data.     

Efficient, solventless N-Boc protection of amines carried out at room temperature using sulfamic acid as recyclable catalyst

A simple, rapid, and efficient protocol for the chemoselective N-Boc protection of amines using sulfamic acid as catalyst is described. N-Boc protection of various structurally diverse aliphatic, aromatic, alicyclic, and heterocyclic amines (1°, 2°, 3°) was carried out with (Boc)₂O using sulfamic acid as catalyst (5 mol %) at room temperature under solventless conditions. The advantages of this method are simplicity, shorter reaction times (1-15 min), a cost-effective catalyst, and excellent isolated yields (90-100%); it is also environmentally benign. Moreover, the combined use of ultrasound and sulfamic acid achieves a synergic effect that is especially marked in the N-Boc protection of deactivated (sterically hindered and electron-deficient) amines. The catalyst possesses distinct advantages: ease of handling, cleaner reactions, high activity, and excellent chemoselectivity.     

Borylation of aryldiazonium salts at room temperature in an aqueous solution under catalyst-free conditions

A general and convenient borylation reaction of aryldiazonium tetrafluoroborate salts with B₂pin₂ has been developed. In this catalytic system, no catalyst, additional ligands or additives were required. The reaction proceeded smoothly in an aqueous solution, and a variety of arylboronates were isolated in moderate to excellent yields under mild reaction conditions.     

Silica sulfuric acid (SSA) as a solid acid heterogeneous catalyst for one-pot synthesis of substituted pyrroles under solvent-free conditions at room temperature

A variety of N-substituted pyrroles have been synthesized by reacting γ-diketones with amines, diamines or triamine in the presence of silica sulfuric acid (SSA) at room temperature under solvent-free conditions. The experiment protocol features simple operations, and the products are isolated in high to excellent yields (70-98%).     

Epoxidation of vinyl cyanides by calcium hypochlorite under catalyst- and solvent-free conditions

In this paper, epoxidation of a wide range of alkenes by calcium hypochlorite (Ca(OCl)₂) was investigated under catalyst- and solvent-free conditions. It was noticed that the highest yield was achieved with crushing, when the reaction was between vinyl cyanides and Ca(OCl)₂. The structure of the synthesized epoxides was confirmed by IR, ¹H and ¹³C NMR and elemental analysis. Short reaction times, the use of a simple experimental procedure, and reducing of energy consumption are other important advantages of our work that could be mentioned too.     

An efficient and solvent-free one-pot synthesis of dihydropyrimidinones under microwave irradiation

An efficient synthesis of 3,4-dihydropyrimidin-2(1H)-one derivatives using formic acid as catalyst, from aldehydes,β-ketoester and urea(thiourea) without solvent under the irradiation of microwave is described. Compared with the classical Biginelli reaction, this new method has the advantage of good yields (77-94% for aromatic aldehydes) and short reaction time (3-8 min).     

A simple approach to benzothiazoles from 2-chloronitrobenzene,elemental sulfur,and aliphatic amine under solvent-free and catalyst-free conditions

A novel solvent-free and catalyst-free synthesis of benzothiazoles from 2-chloronitrobenzene, elemental sulfur, and aliphatic amine has been developed. The reaction tolerated a wide range of functionalities, and various benzothiazoles were synthesized in moderate to good yields in the absence of external oxidant or reductant.     

An environmentally friendly procedure for Mukaiyama aldol and Mukaiyama-Michael reactions using a catalytic amount of DBU under solvent- and metal-free conditions

Mukaiyama aldol and Mukaiyama-Michael reactions can proceed smoothly in the presence of a catalytic amount of DBU (20% mmol), to afford the corresponding products in moderate to good yields. This solvent- and metal-free approach provides an environmentally friendly procedure for Mukaiyama reactions.