1,3‐Dipolar cycloadditions of (4R*,5R*)‐1‐alkylidene‐4‐(benzoylamino)‐5‐phenyl‐3‐pyrazolidinon‐1‐azomethine imines

1,3-Dipolar cycloadditions of azomethine imines 3a and 3b, available by acid-catalyzed treatment of 3-pyrazolidinone 1 with acetone (2a) and butyraldehyde (2b), respectively, were studied. Reactions of 3a with DMAD (4) afforded a mixture of products 9 and 10a, whilst treatment of 3b with DMAD (4) gave a mixture of compound 9 and epimeric cycloadducts 10/10′b. On the other hand, cycloadducts 13a,b-16a,b were isolated as single diastereomers in 9–37% yields upon reactions of 3a,b with olefinic dipolarophiles 5–8. The structures of cycloadducts 9, 10a, 10/10′b, and 13a,b-16a,b were determined by 1H nmr and NOESY spectroscopy. The structure of compound 13a was confirmed by X-ray diffraction.