Stereoselective Synthesis of Mechanically Planar Chiral Rotaxanes

Abstract

Chiral interlocked molecules in which the mechanical bond provides the sole stereogenic unit are typically produced with no control over the mechanical stereochemistry. Here we report a stereoselective approach to mechanically planar chiral rotaxanes in up to 98:2 d.r. using a readily available α‐amino acid‐derived azide. Symmetrization of the covalent stereocenter yields a rotaxane in which the mechanical bond provides the only stereogenic element.

Chiroptical inversion of a planar chiral redox-switchable rotaxane

“…32 Today, sophisticated synthetic protocols allow an efficient enantioselective synthesis. For example, Goldup and co-workers 33,34 described elegant protocols to synthesise planar chiral enantiopure [2] rotaxanes using readily available chiral auxiliaries. However, switchable planar chiral rotaxanes remain rare.…”

Weak functional group interactions revealed through metal-free active template rotaxane synthesis

“…Active template synthesis [24][25][26][27][28][29][30][31][32][33][34][35] , in which a macrocycle accelerates a strand-forming reaction through the ring cavity, does not require strong pre-association of the starting materials. Although most active template syntheses have been developed from transition metal catalyzed reactions [24][25][26][27][28][29][30][31][32][33][34][35] , a metal-free active template system was recently discovered 36,37 in which the addition of primary amines to electrophiles can be significantly accelerated through crown ethers 37 and related macrocycles 36 by stabilization of the reaction transition state [38][39][40][41][42][43] . The reaction of a primary amine and an electrophile in the presence of a crown ether was found 37 to form [2]rotaxanes by metal-free active template Nalkylation, aza-Michael addition or N-acylation.…”

Modulating the expression of chirality in a mechanically chiral rotaxane

“…1a). [7][8][9] Noteworthy recent achievements with chiral MIMs include the successful preparative scale preparation of enantiopure mechanically chiral rotaxanes without resorting to chiral HPLC for the separation of enantiomers; 10,11 chiral MIMs being used as enantioselective receptors and asymmetric catalysts; [12][13][14][15][16][17][18][19] and induction of single-handed helicity of a polymer by use of a mechanically chiral rotaxane as the source of chirality. 20 MIMs are perhaps most well-known for the possibilities of controlled large amplitude motion of their interlocked components, through either change of environment, or application of a stimulus.…”