Substrate‐Controlled [5+1] Annulation of 5‐Amino‐1H‐phenylpyrazoles with Alkenes: Divergent Synthesis of Multisubstituted 4,5‐Dihydropyrazolo[1,5‐a]quinazolines

A new and efficient [5+1] annulation reaction for the first synthesis of 5,5‐disubstituted 4,5‐dihydropyrazolo[1,5‐ a ]quinazolines is described. This transition‐metal‐free tandem cyclization was performed with 5‐amino‐1 H ‐phenylpyrazole and readily available electron‐deficient olefinic ester. The reaction proceeds via an aza‐Michael addition/Truce‐Smiles rearrangement/S N Ar cyclization pathway, which was verified by DFT calculations. The participation of Truce‐Smiles rearrangement is substrate dependent and could prompt the process of cascade reactions. It is also the first report of alkenes acting as one‐carbon synthons for [5+1] hetero‐annulations.