Synthesis of Pyrazolidines via GaCl₃-Catalyzed Insertion of Diazines into Cyclopropanes

Significance

A facile synthesis of pyrazolidines by reaction of cyclopropane 1,1-diesters and alkyl and ester diazines is reported. The yields are modest and regiochemically selective insertion of the diazine (when R₂ ∂ R₃) is not achieved. Use of cis-diazines (4-phenyl-1,2,4-triazoline-3,5-dione) resulted in mixtures of pyrazolidines with major C-1-C-2 insertion products. The mechanism proposed involves GaCl₃-catalyzed ring opening of the cyclopropane ring followed by insertion of the diazine. Investigation of the mechanism produced no conclusive evidence.