Domino β‐C−H Functionalization and [3+2] Cycloaddition for Efficient Synthesis of Diverse Spiro and Polycyclic Compounds

The acetic acid catalyzed three‐component reaction of pyrrolidine, aromatic aldehydes and 4‐arylidene‐5‐methyl‐2‐phenylpyrazol‐3‐one in refluxing toluene gave functionalized 7′‐( E )‐benzylidenespiro[pyrazole‐4,1′‐pyrrolizines] in good yields and with high diastereoselectivity. The similar reaction with 2‐arylidene‐ N,N’ ‐dimethylbarbiturates resulted in mixture of Z/E ‐isomers of 7′‐ arylidenespiro[pyrimidine‐5,1′‐pyrrolizines] in good yields. However, the three‐component with N ‐phenylmaleimides and sequential oxidation with DDQ reaction gave 8‐( E )‐arylidenedihydropyrrolo[3,4‐ a ]pyrrolizines in satisfactory yields. The reaction mechanism included sequential β‐C−H functionalization of pyrrolidine, generation of conjugated azomethine ylides, and sequential [3+2] cycloaddition with active alkenes.