Substrate-Switched Chemodivergent Pyrazole and Pyrazoline Synthesis: [3 + 2] Cycloaddition/Ring-Opening Rearrangement Reaction of Azadienes with Nitrile Imines.

By virtue of a fundamentally new reaction model of benzofuran-derived azadienes (BDAs), an unprecedented synthesis of biologically important pyrazoles has been achieved through a tandem [3 + 2] cycloaddition/ring-opening rearrangement reaction of BDAs with nitrile imines. The nature and type of substrates are found to act as a chemical switch to trigger two distinct reaction pathways. A minor modification to the substrates allows the access to spiro-pyrazolines.