**4. Conclusions**

In conclusion, we have developed an efficient cycloaddition of a variety of α-nitroketones with alkenes or alkyne using inexpensive and gentle acid. Among the synthesized compounds, the yield of cycloaddition products of substituted phenylnitroketone is high (66–90 %), while the yield of cycloaddition products of alkyl nitroketones (such as **7a**–**b**) is low (20–23 %). This synthesis is based on cycloaddition 1,3-dipolar in presence of *p*-TsOH, which is attractive that the low cost, simple synthetic route, and ease of handling of the gentle acid. It is particularly noteworthy that the reaction provides an effective synthesis method for 3-carbonylisoxazolines. The development of other methods for the synthesis of 3-carbonylisoxazoline is currently under investigation and will be disclosed in due course.

**Supplementary Materials:** The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/molecules28062565/s1, The Supplementary Materials contain experimental protocols, analytical data for products and NMR spectra [29,42,46,48–50].

**Author Contributions:** Conceptualization, X.P., X.Y., and J.W.; methodology, X.P. and X.X., formal analysis, C.Y., X.P.; K.Y.; S.H., K.Z., Q.L., X.X., and J.L.; original manuscript writing, C.Y. and X.P.; revision and supervision, X.P., X.Y., and J.W.; funding acquisition, X.P., X.Y., and J.W. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was by National Natural Science Foundation of China (82160651); The Open Project of Stake Key Laboratory of Natural and Biomimetic Drugs, Peking University (K202103); The Open Project of Key Laboratory of Xinjiang Phytomedicine Resource and Utilization, Ministry of Education (XPRU202004); Youth Innovative Talent Cultivation Projects of Shihezi University (CXPY202005); The National Innovation and Entrepreneurship Training Program for Undergraduate (202210759029); and The Open Sharing Fund for the Large-scale Instruments and Equipments of Shihezi University.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available in the article and Supplementary Materials.

**Acknowledgments:** The authors thank Liang Guo for assistance with NMR.

**Conflicts of Interest:** The authors declare no conflict of interest.

**Sample Availability:** Samples of the compounds **3a-i**, **5a-f**, **7a-b** and **9a-b** are available from the authors.
