Regioselective Synthesis of Mono- and Dispiropyrazoline Derivatives via 1,3-dipolar Cycloaddition with Nitrilimines

The 1,3-dipolar cycloaddition reaction of (E,E)-1,3-bis(arylidene)indan-2-one 1a, 1b, 1c, 1d, 1e with diarylnitrilimines, generated in situ via dehydrohalogenation of the corresponding hydrazonoyl chlorides 2a, 2b, 2c, affords predominantly monospiropyrazolines 3 and 4 as a mixture of diastereoisomers. Also dispiropyrazolines 5 are formed in moderate yields. The structure and stereochemistry of cycloadducts 3, 4, 5 were confirmed by H-1 and C-13-NMR spectroscopy, elemental analyses data, and single-crystal X-ray diffraction studies of 3ba and 5ca.