Structure-Dependent,\nSwitchable Alder-Ene/[2π\n+ 2σ] Cycloadditions of Vinyl Bicyclo[1.1.0]butanes with α‑Ketoesters\nEnabled by Palladium Catalysis

A structure-dependent, palladium-catalyzed switchable\nalder-ene/[2π\n+ 2σ] cycloaddition of VBCBs with α-ketoesters has been\nreported. A variety of cyclobutenes and 2-oxabicyclo[2.1.1]hexanes\nhave been efficiently achieved in good to excellent yields through\nstrain-release-driven alder-ene reactions and [2π + 2σ]\ncycloadditions, respectively. The potential of this method is illustrated\nby the scale-up reaction and diverse postsynthetic transformations\nof the obtained cyclic scaffolds. Additionally, the reaction mechanism\nand origins of the chemoselectivity have been probed by computational\nstudies.