Convenient Synthesis of Functionalized Spiropyrazolone‐Fused Pyrazolo[1,5‐ <i>c</i> ]Quinazolines via Catalyst‐Free (3 + 2) Cycloaddition of Quinazoline‐Derived Azomethine Imines With Arylidene Pyrazolones

ABSTRACT In this paper, we developed a straightforward protocol for catalyst‐free (3 + 2) cycloaddition between quinazoline‐derived azomethine imines and arylidene pyrazolones to provide a series of spiropyrazolone‐fused pyrazolo[1,5‐ c ]quinazolines with yields ranging from moderate to good. These products possess three contiguous stereocenters, including a quaternary carbon center, and exhibit excellent regio‐ and diastereoselectivity (up to &gt; 25:1 dr). Moreover, this approach entails the utilization of readily accessible starting materials, encompasses a wide range of substrates, operates under mild reaction conditions, and offers the advantages of simple operational procedures and 100% atom economy. Additionally, the novel privileged structures incorporating spiropyrazolone and pyrazolo[1,5‐ c ]quinazoline motifs demonstrate potential to be MEP1B inhibitors through a molecular docking study. The structural framework and relative configuration of the representative product were conclusively determined through single‐crystal x‐ray diffraction analysis.