Spirocyclopropane-oxindoles are key motifs in biologically active compounds and are versatile synthetic intermediates. Herein, we report a metal-free, B(C6F5)3 catalyzed cyclopropanation of 3-alkenyl-oxindoles with diazomethanes. This provides 25 variants of spirocyclopropane-oxindole derivatives. These spirocyclopropane-oxindole products were obtained in good to excellent yields (up to 99%) and high diastereoselectivities (up to 20 : 1 d.r.) under mild reaction conditions and could be performed on a gram scale.