Temperature-Controlled Divergent Reactions of Bicyclo[1.1.0] butanes with Thiocyanate-based Protic Ionic Liquids

Abstract

Bicyclo[1.1.0]butanes (BCBs), with their exceptional ring strain, serve as versatile precursors for complex molecular architectures, yet sustainable activation strategies remain limited. Herein, we report a protic ionic liquid (HMimNCS) that simultaneously serves as solvent, Brønsted acid, and nucleophile, enabling an environmentally benign and operationally simple strategy for BCB activation and functionalization without metal catalysts. The system exhibits temperature-controlled divergent reactivity: mild conditions produce kinetically favoured thiocyanatocyclobutanes, while elevated temperatures generate phenyl-stabilised carbocationic-like intermediates, driving rearrangement to thermodynamically favoured isothiocyanatocyclobutanes. Base-mediated transformations afford a new class of heterobicyclic scaffolds, 2-azabicyclo[2.1.1]hexane-3-thiones. Mechanistic investigations clarify the sequential BCB activation and temperature-dependent divergent pathways. Remarkably, a newly developed selenium-based ionic liquid (HMimNCSe) mirrors these outcomes, expanding the strategy to seleno analogues. Late-stage functionalization highlights versatility, while recyclable ionic liquids and temperature-controlled selectivity define a sustainable activation platform aligned with green chemistry.