Temperature-Controlled Divergent Hydroamination Cyclization [2+2]-Cycloaddition Cascade Reactions of Homopropargylic Amines with 2‑Butynedioates: Direct Access To Pyrrolo‑b‑cyclobutene and Dihydro‑1H‑azepines

The diversified temperature-controlled hydroamination cyclization cascade reactions of homopropargylic amines and 2-butynedioates were developed for the construction of various pyrrolo-b-cyclobutenes and dihydro-1H-azepines, respectively. This reaction actually involved an intramolecular hydroamination cyclization of homopropargylic amines to give the active dihydropyrroles intermediates, which subsequently underwent [2+2]-cycloaddition with 2-butynedioates to generate the pyrrolo-b-cyclobutenes at no more than 120 °C. Alternatively, the dihydro-1H-azepines were directly produced at 150 °C in the reactions of homopropargylic amines and 2-butynedioates. The application of substrate scope was wide, and the corresponding products were obtained in high to excellent yields.