Controllable Si−C Bond Activation Enables Stereocontrol in the Palladium‐Catalyzed [4+2] Annulation of Cyclopropenes with Benzosilacyclobutanes

A novel and unusual palladium‐catalyzed 4+2] annulation of cyclopropenes with benzosilacyclobutanes is reported. This reaction occurred through chemoselective Si?C(sp²) bond activation in synergy with ring expansion/insertion of cyclopropenes to form new C(sp²)?C(sp³) and Si?C(sp³) bonds. An array of previously elusive bicyclic skeleton with high strain, silabicyclo4.1.0]heptanes, were formed in good yields with excellent diastereoselectivity under mild conditions. An asymmetric version of the reaction with a chiral phosphoramidite ligand furnished a variety of chiral bicyclic silaheterocycle derivatives with good enantioselectivity (up to 95.5:4.5 er). Owing to the mild reaction conditions, the good stereoselectivity profile, and the ready availability of the functionalized precursors, this process constitutes a useful and straightforward strategy for the synthesis of densely functionalized silacycles.