HFIP-Mediated Spiro-annulation of Bicyclo[1.1.0]butanes with α-Halo Hydroxamates: Access to Functionalized Spirocyclobutenes

Bicyclo[1.1.0]butanes (BCBs) are activated using photocatalysts, Lewis and Brønsted acids, transition metal catalysts, and more recently hexafluoroisopropanol (HFIP). On the other hand, α-halo hydroxamates are known to generate reactive azaoxyallyl cations in the presence of HFIP. Herein, we merge the BCB activation and azaoxyallyl cation stabilization using HFIP for the metal- and photocatalyst-free spiro-annulation of BCBs with α-halo hydroxamates, enabling efficient access to functionalized spirocyclobutenes. Mechanistic studies highlight the dual role of HFIP, thereby unveiling a unique reactivity mode and expanding the synthetic potential of strained molecular frameworks.