6π 1,5-Diaza-electrocyclization of Isatin, α-Ketoester Derived Hydrazones with α,β-Unsaturated Ketoesters, Ketones, and Aldehydes Enables Functionalized Pyrazoles

A novel and efficient 6π 1,5-diaza-electrocyclization of readily available isatin, α-ketoester derived hydrazones with α,β-unsaturated ketoesters, ketones, and aldehydes has been developed. A series of functionalized pyrazoles bearing an oxindole unit were easily afforded by this tool with good yields and high functional group tolerance under mild conditions. Importantly, the obtained pyrazole could be further converted to 3-pyrazolecarboxylic acid with a quaternary carbon stereocenter.