A Synthetic Method for Spirocyclobutanes via Ring Expansion of Donor–Acceptor Spirocyclopropanes with Stabilized Sulfonium Ylides

A sulfonium ylide-mediated ring expansion of donor-acceptor spirocyclopropanes has been developed to provide access to spirocyclobutanes. Spirocyclopropanes derived from 1,3-indandione undergo efficient ring expansion with stabilized sulfonium ylides, affording the corresponding spirocyclobutanes as single isomers in high yield. Given that spirocyclic frameworks, with their rigid three-dimensional architecture, play a key role in drug discovery, spirocyclobutanes represent particularly promising core structures. This synthetic method is expected to make a significant contribution to pharmaceutical development.