An Isoxazole Strategy for the Synthesis of Fully Substituted Nicotinates

Metal carbonyl mediated rearrangement of 5-(2-oxoalkyl)-1,2,4-oxadiazoles: synthesis of fully substituted pyrimidines

Variously substituted ethyl 6-oxo-1,6-dihydropyrimidine-5-carboxylates can be easily prepared by a metal carbonyl mediated rearrangement of ethyl 3-oxo-2-(1,2,4-oxadiazol-5-yl)propanoates. The irradiation of a mixture of oxadiazoles and Fe(CO)₅ in wet solvents with a 365 nm LED at room temperature for 2 h followed by heating at 80 °C for 2 h gives pyrimidines in up to 90% yield. This procedure enables the preparation of 6-oxo-1,6-dihydropyrimidine-5-carboxylates with various aryl substituents at the C2 and alkyl or aryl substituents at the C4 position. 1-(1,2,4-Oxadiazol-5-yl)propan-2-ones analogously give 6-methylpyrimidin-4(3H)-ones, albeit in lower yields. Ethyl 6-oxo-1,6-dihydropyrimidine-5-carboxylates can be easily modified at the C6 position by bromination followed by cross-coupling reactions to give pyrimidine-5-carboxylates with pyridyl, amino and ethynyl substituents.

Assembly of isoxazol-5-one with 2-unsubstituted imidazole N-oxides and aldehydes

A new synthetic protocol has been developed to construct polyfunctional isoxazol-5-one derivatives with imidazole moiety. It is based on the Knoevenagel condensation of isoxazol-5-one with aldehydes and subsequent Michael addition of imidazole N-oxides as part of a tandem three-component process. This reaction proceeds smoothly in moderate-to-good yield under catalyst-free conditions.

A green protocol for the one-pot synthesis of 3,4-disubstituted isoxazole-5(4H)-ones using modified β-cyclodextrin as a catalyst

This manuscript reports an impressive and facile strategy for synthesizing isoxazole derivatives using immobilized Cu (I) in metformin-functionalized β-cyclodextrin as a catalyst. The architecture of this catalyst was characterized by different analytical techniques such as Fourier transform infrared spectroscopy, Thermogravimetric analysis, X-ray diffraction, Field emission scanning electron microscopy, and Energy-dispersive X-ray spectroscopy. The catalyst showed remarkable reusability even after 7 consecutive runs.

Reaction of α-Diazopyrroles with Enamines: Synthesis of Pyrrolo[2,1-c][1,2,4]triazines and α-(1,2,5-Triazapenta-1,3-dienyl)pyrroles

α-Diazopyrroles selectively react with enamines at room temperature to give either (4+2)-cycloaddition-dehydroamination cascade products, pyrrolo[2,1-c][1,2,4]triazines, or azo coupling products. The reaction was used for the synthesis of functionalized ortho-fused heterocycles with new tetrahydrobenzo[e]pyrrolo[2,1-c][1,2,4]triazine and tetrahydro-6H-cyclohepta[e]pyrrolo[2,1-c][1,2,4]triazine frameworks. Unstable azo compounds, 2-[(2-aminovinyl)diazenyl]pyrroles, were obtained from enamines of tetralone or acyclic ketones. According to the density functional theory calculations, (4+2)-cycloaddition of α-diazopyrroles with enamines proceeds in a nonconcerted manner via the zwitterionic intermediate, which undergoes cyclization to pyrrolotriazine or a competitive 1,5-prototropic shift leading to the formation of azo coupling product.

Access to β-Alkylated γ-Functionalized Ketones via Conjugate Additions to Arylideneisoxazol-5-ones and Mo(CO)6-Mediated Reductive Cascade Reactions

1,4-Conjugate addition of ((chloromethyl)sulfonyl)benzenes to arylideneisoxazol-5-ones, followed by one-pot, N-selective trapping in the presence of electrophiles, was investigated. This strategy led to the synthesis of new, stable N-protected isoxazol-5-ones in good yields and high diastereolectivity. The study of the reactivity of obtained products in the presence of the Mo(CO)₆/H₂O system allowed the development of a cascade reaction leading to novel methyl ketones in high yields and unchanged dr bearing an uncommon chloromethinearylsulfonyl end group.