Journal of Chemical Research

The stereochemistry of some rearrangement reactions of the diterpenoid plant hormone gibberellic acid, including the allylic rearrangements of substituents and the lactone in ring A, rearrangements involving ring B and the Wagner–Meerwein rearrangements of rings C and D, are reviewed.

A green and efficient method for oxazine ring formation is established using the reaction of 2-hydroxy-1,4-naphthoquinone and aromatic aldehydes with methyl carbamate catalysed by p-toluenesulfonic acid in aqueous media to afford 4-aryl-3,4-dihydronaphtho[3,4-e][1,3] oxazine-2,5,10-triones in excellent yields. The salient features of this protocol are short reaction times and high yields while avoiding any hazardous organic solvent. Therefore, this procedure could be classified as green chemistry.

Salpleflavone, a new flavone glucoside bearing a sinapinoyl moiety, was isolated from the aerial parts of Salvia plebeia R. Br., together with three known compounds, salplebeone A, salplebeone D and 6-O-methyl-scutellarein. The structure of the new compound was established by detailed analyses of the spectroscopic data, especially 1D and 2D NMR and HR-ESI-MS.

A number of 2-aryl-2H-chromene-4-carbonitriles were synthesised by cyanation of 2-aryl-3-nitro-2H-chromenes using trimethylsilyl cyanide (TMSCN) in the presence of tetrabutylammonium fluoride (TBAF) in moderate yields via a Michael addition/elimination pathway. The structures of all the products were characterised thoroughly by NMR, IR and HRMS spectroscopy and X-ray crystallographic analysis.

A rhodium/sulfinyl-based olefin ligand-catalysed asymmetric conjugate addition of arylboronic acids to cyanoalkenes without activation groups has been developed, where p-tolylsulfinyl-functionalised olefin ligands have been shown to be effective and with moderate enantioselectivities. This is the first example of applying chiral sulfinyl-based olefin ligands in the catalytic asymmetric addition to cyanoalkenes.

A novel dithienylethene amide-based photoswitchable anion receptor was synthesised by amidation of 4,4′-(cyclopent-1-ene-1,2-diyl) bis(5-methylthiophene-2-carboxylic acid) with 4-nitroaniline in 56% yield under mild conditions; its structure was confirmed by NMR, MS and elemental analysis. Investigation of its photochromic properties indicated that 4,4′-(cyclopent-1-ene-1,2-diyl)bis[5-methyl-N-(4-nitrophenyl) thiophene-2-carboxamide] had good reversibility and excellent fatigue resistance upon irradiation with UV or visible light and can serve as a colorimetric sensor for fluoride, resulting in a significant change in the absorption spectrum.

The title compound, 4-(3-amino-4-morpholino-1H-indazole-1-carbonyl)benzonitrile was synthesised by condensation of 4-cyanobenzoic acid with 4-morpholino-1H-indazol-3-amine, which was prepared from 2,6-difluorobenzonitrile by amination with morpholine and then cyclisation with hydrazine hydrate. The crystal structure of the title compound was determined and the crystals belong to the monoclinic system, space group P2₁/c. In addition, the compound showed some inhibition of the proliferation of some cancer cell lines.

A four-component reaction was investigated to prepare potassium arylmethylene-4-(1H-pyrazol-5-ol)-4′-(1H-pyrazol-5-olate) derivatives from dialkyl but-2-ynedioates, phenylhydrazine, substituted benzaldehydes and potassium carbonate without any catalyst or promoter. The structure of a typical product was confirmed by X-ray crystallography. The advantages of the present methodology are efficiency, broad scope, operational simplicity, high yields and mild reaction conditions.

N¹-substituted octahydro-1H-pyrano[2,3-d]pyrimidines derivatives were prepared in moderate yield by the reaction of methyl [(4aRS,5SR,10aRS)-5-aryl-2-oxo-3,4,4a,10a-tetrahydro-2H,5H-pyrano[3,2-e][1,3]thiazolo[3,2-a]pyrimidin-8(9H)-ylidene]acetate and 2,6-dichorobenzonitrile oxide via a domino 1,3-dipolar cycloaddition/ring-opening/dethionation process. The structures of the products were characterised by spectroscopic and X-ray crystallographic analysis.

A series of new chiral-bridged N-heterocyclic carbene ligands with different substituents and their corresponding palladium complexes have been synthesised. The effect of the substituents on the catalytic activity of these Pd complexes was investigated in the Suzuki reaction of p-bromotoluene with phenylboronic acid, and the results showed that the complexes with aryl substituents performed better than those with alkyl substituents. The complex with the most sterically hindered substituent (diisopropyl on a phenyl group) performed best, and it was also an efficient catalyst for the reaction of various arylboronic acids with aryl halides having different electronic and steric properties. In addition, it was employed as a catalyst in the asymmetric Suzuki reaction, but only moderate yields of 1,1-binaphthalenes with less than 20% enantiomeric excess were obtained.

A one-pot method for the preparation of new 4-aryl-2-thioxo-3,4-dihydropyrimidines via a three-component reaction of Meldrum's acid with arylaldehydes and acetylthiourea in the presence of p-toluenesulfonic acid as catalyst in CH₃CN under reflux is reported.

The synthesis of 2-substituted benzimidazoles from the reaction of o-phenylenediamine and an imino ester hydrochloride with ultrasound irradiation is reported. The procedure has an eco-friendly and simple workup with good yield in a short time.

6-Chloro-3-((2-oxo-5-phenylfuran-3(2H)-ylidene)methyl)-4H-chromen-4-one was utilised for the construction of N-heterocycles. The proclivity of this furanone towards some nitrogen nucleophiles, i.e. glycine, thiosemicarbazide, thiocarbohydrazide, phenylhydrazine and o-phenylenediamine, was studied. The structures of all products obtained were established on the basis of their analytical and spectral data. All synthesised compounds were screened for their in vitro antibacterial (two strains of bacteria; Escherichia coli and Staphylococcus aureus) and antifungal (two fungus strains; Aspergillus flavus and Candida albicans) activities. Some products exhibited promising antimicrobial activities.

14-Aryl-14H-dibenzo[a,j]xanthenes and 1,8-dioxo-octahydroxanthenes were synthesised directly from benzyl alcohols by a tandem catalytic process using choline peroxydisulfate (ChPS). The synthesis proceeds through two steps: an oxidation of the benzyl alcohol to the corresponding benzaldehyde followed by condensation with 2-naphthol (or dimedone) to form the products. Choline bisulfate, generated in situ from ChPS, catalyses the product formation.