Stereoselective 1,3‐Dipolar Cycloaddition of Nitrile Oxides With 9α‐Hydroxy‐1β,10α‐epoxyparthenolide: A Combined Experimental and DFT Study

ABSTRACT New derivatives of spiroisoxazolines were synthesized via a 1, 3‐dipolar cycloaddition reaction between various nitrile oxides and 9α‐hydroxy‐1β,10α‐epoxyparthenolide. The natural epoxide precursor, 9α‐hydroxy‐1β,10α‐epoxyparthenolide, was obtained through the stereoselective epoxidation of the natural product 9α‐hydroxyparthenolide, which was isolated in grams from the aerial parts of Anvillea radiata . This approach underscores the versatility of natural product derivatives in constructing novel heterocyclic compounds with potential biological activity. The structures of all products have been characterized by 1 H NMR, 1 3 C{ 1 H} NMR spectral analysis, and high‐resolution mass spectrometry (HRMS). Notably, the molecular structure of compound 5e was unambiguously established by single‐crystal x‐ray diffraction analysis, providing detailed insight into its stereochemistry and solid‐state conformation. Furthermore, density functional theory (DFT) calculations were employed to investigate the chemical reactivity of the 1,3‐dipolar cycloaddition between compound 2 and nitrile oxide 3a , and the results confirmed the experimental findings.