A rapid synthesis of isoxazolo[5,4-d]pyrimidin-4（5H）-ones under microwave irradiation with solid acid catalysis in solvent-free conditions

A rapid and efficient method for the synthesis of isoxazolo[5,4-d]pyrimidin-4（5H）-ones has been developed through cyclocondensation of 5-aminoisoxazole-4-carboxamides with orthoesters under conventional heating and solvent-free microwave irradiation with solid acid catalysis. In comparison, the reactions are faster and the yields are higher under microwave irradiation.     

Phosphated tungstate: An efficient new solid phosphoric acid catalyst for the synthesis of heterocyclic nitrones

Phosphated tungstate as a new, reusable and efficient solid phosphoric acid catalyst was synthesized and used to promote the reaction of diaminoglyoxime with various aromatic aldehydes. The prepared phosphated tungstate was characterized using various techniques including X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, Fourier transform infrared spectroscopy and thermal analysis. A wide variety of heterocyclic nitrones were obtained under mild reaction conditions and in high yields by using the prepared catalyst.     

A green synthesis of nitrones from diamino glyoxime using aldehydes and ketones

The reaction of diaminoglyoxime with aldehyde and ketone derivatives in the presence of p-toluene sulphonic acid in H₂O–MeOH mixture at room temperature afforded nitrone derivatives in high yields within 10–140 min. The applicability of ketones in this reaction for the preparation of novel nitrones has been verified. The effect of the temperature on the stability of the structural isomers of the products has been studied by NMR as well. The results showed that, at high temperatures only one product could be observed. The nature of solvent and catalyst were evaluated and found that the strong acids H₂SO₄ and CF₃SO₃H in protic solvent CH₃OH work well while neither CH₃SO₃H in protic solvent nor p-toluene sulphonic acid in aprotic solvents toluene and THF perform the same reactions.     

Efficient Reduction of Nitroarenes to the Corresponding Anilines with Sulfur in Basic Media under Solvent-Free Conditions

Aromatic nitro compounds can be conveniently reduced to the corresponding primary amines in the presence of S 8 under solvent-free conditions in excellent yields. Alumina supported NaOH catalyses this transformation. Chemoselectivity was observed in the reduction of the nitro group in the presence of phenol, carboxylic acid, aldehyde, and benzyl halide groups.     

Fe(HSO4)3 and Fe(HSO4)3/DMSO as Efficient,Heterogeneous, and Reusable Catalyst Systems for the Oxidative Coupling of Thiols

Fe(HSO₄)₃ has been used as a heterogeneous, efficient, and recyclable catalyst in ethanol for the selective oxidation of thiols to their corresponding disulfides. The same results were obtained under identical conditions using catalytic amounts of Fe(HSO₄)₃ in the presence of DMSO. Different types of aliphatic, aromatic, and heteroaromatic thiols have been used in the reaction, and in all cases the products were obtained in good to excellent yields.     

One-pot synthesis of 2-amino-3-cyano-4-arylsubstituted tetrahydrobenzo[<Emphasis Type="Italic">b</Emphasis>]pyrans catalysed by silica gel-supported polyphosphoric acid (PPA-SiO<Subscript>2</Subscript>) as an efficient and reusable catalyst

A convenient method for the synthesis of tetrahydrobenzo[b]pyrans by a one-pot three-component cyclocondensation of dimedone, aryl aldehydes, and malononitrile in water using silica gel-supported polyphosphoric acid (PPA-SiO₂) as an efficient and reusable catalyst is described. The present methodology offers several advantages, such as a simple procedure with ease of handling, short reaction time, high yields, and the absence of any volatile and hazardous organic solvents.     

Microwave Assisted Synthesis of 6-Aryl-3-substituted-5H-[1,2,4]-triazolo[4,3-b][1,2,4]triazoles: A Case for a Comparative Study

A simple and fast synthesis of 6-aryl-3-substituted-5H-[1,2,4]-triazolo[4,3-b][1,2,4]triazoles 4 in high yields has been developed by microwave assisted heterocyclization of N-(3-methylthio-5-substituted-4H-1,2,4-triazol-4-yl)benzenecarboximidamides 3 . The effectiveness of the microwave irradiation and conventional heating for the formation of compounds 4 has been investigated.