Studies on the syntheses of heterocycles from 3-arylsydnone-4-carbohydroximic acid chlorides with N-arylmaleimides, [1,4]naphthoquinone and aromatic amines

3-Arylsydnone-4-carbohydroximic acid chlorides (1) could react with N-arylmaleimides (3a–b) or 2-methyl-N-phenylmale-imide (3c) to give 3-(3-arylsydnon-4-yl)-5-aryl-3a,6a-dihydro-pyrrolo[3,4-d]isoxazole-4,6-diones (4a–h) or 6a-methyl-3-(3-arylsydnon-4-yl)-5-phenyl-3a,6a-dihydro-pyrrolo[3,4-d]isoxazole-4,6-diones (4i–l), respectively. However, 3-(arylsydnon-4-yl)-naphtho[2,3-d]isoxazole-4,9-diones (6a–d) were obtained in good yield by the reaction of carbohydroximic acid chlorides 1 with [1,4]naphthoquinone. Furthermore, 2-(3-arylsydnon-4-yl)benzoxazoles (9a–d) and 2-(3-arylsydnon-4-yl)benzothiazoles (9e–h) were obtained via the reaction of carbohydroximic acid chlorides 1 with ortho-substituted aromatic amines 7a and b.     

Metal free montmorillonite KSF clay catalyzed practical synthesis of benzoxazoles and benzothiazoles under aerobic conditions

An efficient method for the synthesis of benzoxazoles and benzothiazoles via montmorillonite KSF clay catalyzed condensation reaction between 2-aminophenols or 2-aminothiophenols and β-diketones is reported. The efficiency of the reaction reflects from the wide substrate scope with electronic differentiation on aryls. The reaction is metal free and proceeds without the exclusion of air or moisture, and further the catalyst can be recycled up to 3–5 catalytic cycles.     

(N‐heterocyclic carbene)PdCl(N‐heterocyclic carboxylate) complexes: Synthesis and catalytic activities towards arylation of benzoxazoles with aryl halides

A series of N‐heterocyclic carboxylate‐stabilized N‐heterocyclic carbene palladium complexes have been synthesized and fully characterized. The solid‐state structures indicate that each of the palladium centers is coordinated by an N‐heterocyclic carbene, a chloride and a bidentate N,O‐donor N‐heterocyclic carboxylate ligand. The catalytic performance of the complexes was screened and the results revealed that the complexes exhibit moderate to high catalytic activities for the direct C─H bond arylation of benzoxazoles with aryl bromides.     

Copper‐catalyzed highly efficient aerobic oxidative synthesis of benzimidazoles,benzoxazoles and benzothiazoles from aromatic alcohols under solvent‐free conditions in open air at room temperature

Solvent‐free oxidative synthesis of benzimidazoles, benzoxazoles and benzothiazoles from aromatic alcohols and o‐phenylenediamine, o‐aminophenol and o‐aminothiophenol has been achieved by using CuCl, 2,2′‐bipyridine and TEMPO (2,2,6,6‐tetramethylpiperidine‐1‐oxyl). The reaction proceeds via a dehydrogenation in open air at room temperature, and a wide variety of derivatives were obtained in good to excellent yields. The reaction mechanism was proposed and this method provides a mild and efficient access to substituted benzimidazoles, benzoxazoles and benzothiazoles. Copyright © 2013 John Wiley & Sons, Ltd.     

Iodine‐Mediated Synthesis of 2‐Arylbenzoxazoles, 2‐Arylbenzimidazoles,and 1,3,5‐Trisubstituted Pyrazoles

2‐Arylbenzoxazoles and 2‐arylbenzimidazoles were synthesized by the reaction of aldehydes with 2‐aminophenol and O‐phenylenediamines in the presence of iodine. 1,3,5‐Trisubstituted pyrazoles were synthesized from chalcones and hydrazines in the presence of iodine.     

Expeditious and Efficient Synthesis of Benzoxazoles,Benzothiazoles, Benzimidazoles Catalyzed by Ga(OTf)3 under Solvent‐Free Conditions

A new and efficient method for the synthesis of benzoxazoles, benzothiazoles, benzimidazoles from reactions of o‐substituted aminoaromatics with orthoesters in the presence of catalytic amounts of Ga(OTf)₃ under solvent‐free conditions is presented. The remarkable features of this new protocol are high conversion, very short reaction times, cleaner reaction profiles under solvent‐free conditions, straight forward procedure, and use of relatively non‐toxic catalysts.     

Efficient one-pot synthesis of benzoxazole derivatives catalyzed by Zinc triflate

A simple and efficient method has been developed for the synthesis of benzoxazoles from 2-aminophenol and substituted aldehydes in the presence of a catalytic amount of zinc triflate in ethanol solvent at reflux temperature.     

Comparison of experimental and DFT‐calculated NMR chemical shifts of 2‐amino and 2‐hydroxyl substituted phenyl benzimidazoles,benzoxazoles and benzothiazoles in four solvents using the IEF‐PCM solvation model

A comparative study of experimental and calculated NMR chemical shifts of six compounds comprising 2‐amino and 2‐hydroxy phenyl benzoxazoles/benzothiazoles/benzimidazoles in four solvents is reported. The benzimidazoles showed interesting spectral characteristics, which are discussed. The proton and carbon chemical shifts were similar for all solvents. The largest chemical shift deviations were observed in benzene. The chemical shifts were calculated with density functional theory using a suite of four functionals and basis set combinations. The calculated chemical shifts revealed a good match to the experimentally observed values in most of the solvents. The mean absolute error was used as the primary metric. The use of an additional metric is suggested, which is based on the order of chemical shifts. The DP4 probability measures were also used to compare the experimental and calculated chemical shifts for each compound in the four solvents. Copyright © 2015 John Wiley & Sons, Ltd.