Generation of azaarene nitrile oxides from methyl azaarenes and t-BuONO enabling synthesis of furoxans and 1,2,4-oxadiazoles

A high-efficiency strategy for the synthesis of furoxans and 1,2,4-oxadiazoles has been developed, utilizing tert-butyl nitrite (TBN) as nitrogen sources. Azaarene nitrile oxides as activated intermediates were generated in-situ via...

From α-Keto Acids to Nitrile Oxides Enabled by Copper Nitrate: A Facile Access to Fused Isoxazolines

α-Keto acids were unprecedentedly employed as novel precursors of nitrile oxides on treatment with copper nitrate, which reacted with maleimides via [3+2] dipolar cycloaddition leading to pharmacologically interesting fused isoxazolines....

The 1,3-Dipolar Cycloaddition Reactions of Nitrile Oxides in Water Media

: The 1,3-dipolar cycloadditions (DCs) of nitrile oxides (NOs) have been used as a powerful tool in synthetic organic chemistry. The cycloadducts arising from cycloadditions (CAs) of NOs to alkenes and alkynes (2-isoxazolines and isoxazoles respectively) are valuable synthetic intermediates because, among others, their capacity to mask other functionalities including α, β-unsaturated ketones, β-hydroxy carbonyl compounds and 1,3-aminoalcohols. In particular, the β-hydroxy ketone functionality is an illustrative example, making the NOs alkenes CAs reactions a synthetically equivalent methodology of aldol reactions. The vast majority of these reactions are carried out in organic solvents. Nevertheless, the use of water as an alternative solvent has evident advantages on the “Green Chemistry” concept. The critical discussion on the use of water instead of “conventional” solvents in the 1,3-DCs reactions of NOs is the objective of the present review.

A Facile Approach to the Synthesis of 3-Acylisoxazole Derivatives by the Use of Reusable Solid Acid Catalysts

Nitrile oxides were obtained from α-nitro ketones by the use of silica-gel supported sodium hydrogensulfate (NaHSO4/SiO2) or Amberlyst 15 as solid acid catalyst, and then the corresponding 3-acylisoxaszoles were obtained from alkynes via the 1,3-dipolar ([3+2]) cycloaddition. These heterogeneous catalysts are easily separable from the reaction mixture, and reused up to the synthesis. This synthetic method provides a facile, efficient and reusable production of 3-acylisoxazoles.