Lewis Acid-Catalyzed (3+3) Annulation of Bicyclo[1.1.0]butanes with Mercaptoacetaldehyde: Access to 2-Thiabicyclo[3.1.1]heptanes

Although bicyclo[1.1.0]butanes (BCBs) are widely exploited for the construction of carbocyclic frameworks as well as aza- and oxa-bicyclic scaffolds, analogous sulfur-based transformations remain less explored. Herein, we report a Lewis acid-catalyzed (3+3) annulation of BCBs with in situ-generated mercaptoacetaldehyde, providing access to 2-thiabicyclo[3.1.1]heptanes under mild conditions. This operationally simple protocol exhibits broad applicability and enables the rapid assembly of structurally complex sulfur-containing scaffolds, thereby expanding the scope of BCB chemistry toward biologically relevant architectures.