The synthesis of pyrazolo[1,2‐ a ]pyrazoles. Regio‐ and stereo‐selective 1,3‐dipolar cycloadditions of (1 Z )‐ rel ‐(4 R ,5 R )‐1‐arylmethylene‐4‐benzoylamino‐5‐phenyl‐3‐pyrazolidinon‐1 ‐azomethinimines

Reaction of rel ‐(4 R ,5 R )‐4‐benzoylamino‐5‐phenyl‐3‐pyrazolidinone (4) with aromatic aldehydes 5a‐f gave the corresponding (1 Z )‐ rel ‐(4 R ,5 R )‐1‐arylmethylene‐4‐benzoylamino‐5‐phenyl‐3‐pyrazolidinon‐1‐azomethinimines 6a‐f . 1,3‐Dipolar cycloadditions of azomethinimines 6a‐f to various dipolarophiles, which were found to proceed regio‐ and stereo‐selectively, afforded the corresponding pyrazolo[1,2‐ a ]‐pyrazoles 8a‐f, 10 , and 13–16 . Reaction of azomethinimine 6a with hydrogen cyanide gave rel ‐(5 R ,6 R )‐6‐benzoylamino‐5,6‐dihydro‐3,5‐diphenyl‐1‐oxo‐1 H ,7 H ‐pyrazolo[1,2‐ a ][1,2,3]triazole (18) as a representative of a new ring system.