Facial Selectivity in Mechanical Bond Formation: Axially Chiral Enantiomers and Geometric Isomers from a Simple Prochiral Macrocycle
Peter Gallagher, Andrea Savoini, Abed Saady, John R. J. Maynard, Patrick W. V. Butler, Graham J. Tizzard, Stephen M. Goldup
Abstract
High Resolution Image Download MS PowerPoint Slide In 1971, Schill recognized that a prochiral macrocycle encircling an oriented axle led to geometric isomerism in rotaxanes. More recently, we identified an overlooked chiral stereogenic unit in rotaxanes that arises when a prochiral macrocycle encircles a prochiral axle. Here, we show that both stereogenic units can be accessed using equivalent strategies, with a single weak stereodifferentiating interaction sufficient for moderate to excellent stereoselectivity. Using this understanding, we demonstrated the first direct enantioselective (70% ee ) synthesis of a mechanically axially chiral rotaxane.