The molecular electronic density theory (MEDT) was invested to elucidate the chemo-, regio- and stereo-selectivity of the 1,3-dipolar cycloaddition between Diazomethane (DZM) and Psilostachyin (PSH). The DFT method at B3LYP/6-31 + G (d,p) level of theory was used. Reactivity indices, transition structures theory, IGM and ELF analysis were employed to reveal the mechanism of the reaction. The addition of DZM to PSH takes place through a one-step mechanism and an asynchronous transition states. Eight possible addition channels of reaction were investigated (addition of C (sp2) to Diazomethane at C4, C5, C6 or C7). The addition of C (sp2) at C5 leading to P1 product is the preferred channel. The addition of ether does not affect the chemo-, regio- and stereo-selectivity of the reaction. Analysis of transfer of charges along the IRC path associated with the P1 product shows a polar character for the studied reaction. We have also used the noncovalent interaction (NCI) which is very helpful to reveal the most favored addition channel of the reaction, by analyzing the weak interactions in different TSs. Finally, we investigate about the potential of inhibition of some pyrazoline compounds against COVID-19-M^pro by performing a molecular docking calculations.

分子电子密度理论 (MEDT) 被用来阐明重氮甲烷 (DZM) 和 Psilostachyin (PSH) 之间 1,3-偶极环加成的化学选择性、区域选择性和立体选择性。使用B3LYP/6-31+G(d,p)理论水平的DFT方法。采用反应指数、过渡结构理论、IGM和ELF分析来揭示反应机理。 DZM 添加到 PSH 是通过一步机制和异步转换状态进行的。研究了八种可能的反应加成通道（将 C (sp2) 加成至重氮甲烷的 C4、C5、C6 或 C7）。在 C5 处添加 C (sp2) 产生P1产物是首选通道。添加醚不会影响反应的化学选择性、区域选择性和立体选择性。对P1产物沿 IRC 路径的电荷转移分析显示了所研究反应的极性特征。我们还使用了非共价相互作用（NCI），通过分析不同 TS 中的弱相互作用，这非常有助于揭示反应最有利的加成通道。最后，我们通过分子对接计算研究了一些吡唑啉化合物对 COVID-19-M ^pro的抑制潜力。