Diastereoselective construction of spiro-cyclopropyl-pyrazoles <i>via</i> a [2 + 1] annulation reaction of iminoindoline-derived alkenes and 4-bromo-pyrazolones

A base-promoted [2 + 1] annulation reaction between iminoindoline-derived alkenes and 4-bromo-pyrazolones has been disclosed, affording a series of novel, pharmaceutically interesting spiro-cyclopropyl pyrazolones containing indolines in good to excellent yields with moderate to good diastereoselectivities. This protocol features broad functional group compatibility, simple operation, and mild reaction conditions.