Synthesis of 3C,4R,5T-1,2-Dimethyl-3,5-Diaryl Pyrazolidine-4-Carboxylic Acid via Intermolecular [3 + +2] Cycloaddition †

1,2-Dimethyl-3,5-diarylpyrazolidine-4-carboxylic acid derivatives 4a–d were synthesised stereo-selectively via intermolecular [3⁺+2] cycloaddition of aldehydes 1a–d and 1,2-dimethylhydrazine dihydrochloride (2) with ethyl trans-cinnamate (3), stereochemistries of which were assigned by ¹H-NOESY spectroscopy, and relative configurations confirmed by X-ray diffraction of one of them (4a).