Synthesis of New Pyrazoles via Cycloaddition Reactions of Nitrilimines with 2-Cyclopentenone Derivatives

Compounds 1,3,6,6a‐tetraphenyl‐1,6a‐dihydrocyclopenta[c]pyrazol‐4(3aH)‐ones (3), 1,3,3a,4‐tetraphenyl‐1,3a‐dihydrocyclopenta[c]pyrazol‐6‐ols (4) and 6‐hydroxy‐1,3,6,6a‐tetraphenyl‐1,5,6,6a‐tetrahydrocyclopenta[c]pyrazole‐4(aH)‐one (5) were synthesized by reaction of 3,4‐diphenyl‐4‐hydroxy‐2‐cyclopentenone (2a) with nitrilimines, generated in situ by the action of triethylamine on the corresponding hydrazonyl chlorides 1.