Stoichiometry-controlled cycloaddition of nitrilimines with unsymmetrical exocyclic dienones: microwave-assisted synthesis of novel mono- and dispiropyrazoline derivatives

Microwave-assisted 1,3-dipolar cycloaddition of (E,E)-1,3-bisarylidenetetral-2-ones with nitrilimines, generated in situ by dehydrohalogenation of the corresponding hydrazonoyl chlorides, affords a series of spiropyrazolines in good to excellent yields. The presence of a second exocyclic C=C bond also allows the preparation of dispiropyrazolines. The cycloaddition proceeds with high chemo-, regio- and diastereoselectivity. The structure of the spiranic adducts has been established on the basis of their spectroscopic data and elemental analyses. The stereochemistry of these N-heterocycles has been confirmed by two X-ray diffraction studies. The luminescence properties and fluorescence quantum yields of these heterocyclic compounds have been investigated revealing that some of them are fluorescent in solution.