Stable azomethine imines derived from pyrazolidin-3-one and their cycloaddition to N-arylmaleimides

Reactions of ( Z )-1-arylmethylidene-3-oxopyrazolidin-1-ium-2-ides (stable analogs of azomethine imines generated by thermal opening of the diaziridine fragment in 6-aryl-1,5-diazabicyclo[3.1.0]hexanes) with N -arylmaleimides having no ortho substituents in the aryl group are stereoselective: the products are mixtures of the corresponding cis and trans adducts, the latter prevailing (∼1.4–2.6: 1). trans Adducts are formed as the only products in the reactions with di- ortho -substituted N -arylmaleimides. ( Z )-1-[(2,6-Dichlorophenyl) methylidene]-3-oxopyrazolidin-1-ium-2-ide reacts with both para - and ortho -substituted N -arylmaleimides to give exclusively trans adducts. Labile azomethine imines generated by thermolysis of 6-aryl-1,5-diazabicyclo[3.1.0]hexanes are likely to have Z configuration as well.