Catalytic enantioselective synthesis of mechanically planar chiral rotaxanes by organocatalyzed desymmetrization

Abstract

Mechanical chirality, a non-classical form of molecular chirality arising from the spatial arrangements of component parts connected by mechanical bonds, has been identified in various mechanically interlocked molecules (MIMs), notably represented by mechanically planar chiral (MPC) rotaxanes. Due to their dynamic and inherently chiral properties, MPC rotaxanes have found diverse and promising applications. Despite recent advancements in practical chiral auxiliary-directed asymmetric synthesis, the catalytic enantioselective synthesis of MPC rotaxanes remains a formidable challenge because of the complexity in discriminating mechanical planar chirality and the conformational flexibility of mechanical bonds. In this work, we present an efficient desymmetrization strategy for the catalytic enantioselective synthesis of MPC rotaxanes by integrating rotaxane preorganization through multiple noncovalent interactions and the exceptional stereodiscrimination capabilities of chiral phosphoric acid catalysis, resulting in a broad scope and high enantioselectivities. Notably, the resulting MPC rotaxane products emerge as chiral rotaxane catalysts with tunable reactivity and stereoselectivity.