Dynamic Control of Chiral Space Through Local Symmetry Breaking in a Rotaxane Organocatalyst

Abstract

We report on as witchable rotaxane molecular shuttle that features ap seudo-meso 2,5-disubstituted pyrrolidine catalytic unit on the axle whose local symmetry is broken according to the position of at hreaded benzylic amide macrocycle.T he macrocycle can be selectively switched (with light in one direction;with catalytic acid in the other) with high fidelity between binding sites located to either side of the pyrrolidine unit. The position of the macrocycle dictates the facial bias of the rotaxane-catalyzed conjugate addition of aldehydes to vinyl sulfones.The pseudo-meso non-interlocked thread does not afford significant selectivity as ac atalyst (2-14 %e e), whereas the rotaxane affords selectivities of up to 40 %e ew ith switching of the position of the macrocycle changing the handedness of the product formed (up to 60 % Dee).

Stereodynamics of E/Z isomerization in rotaxanes through mechanical shuttling and covalent bond rotation

“…This area is teeming with opportunities, not only as a consequence of the vastness of its scope but also for the growing role of MIMs in the development of new catalysts, [11][12][13][14] advanced materials, [15][16][17][18] and molecular machines. 1,[19][20][21][22][23] In recent years, the investigation of enantiomerism in MIMs, owing to the central role of chirality in chemistry, has been the main focus of investigations in mechano-stereochemistry, [11][12][13][14][24][25][26] while other forms of stereoisomerism have attracted relatively less attention. 27 In particular, the static and dynamic aspects of cis-trans isomerism in rotaxanes-MIMs minimally composed of a macrocyclic ring encircling an axle-like molecule endowed with bulky end groups too large to pass through the ring opening-are largely unexplored.…”

Control of Dynamic sp3-C Stereochemistry

“…When interfaced with transition metal complexes, the dynamic cage conveys a stereochemical preference to the chiral-at-metal 41,42 centre. Controllable and adaptable sp -carbon stereochemistry of this kind can be exploited in enantioselective synthesis 7,9,10,28,38,47,48 and chiral functional materials. 49…”

“…However, they do so without external control of their rate or direction to a single stereoisomer. Only multicomponent interlocked molecules, in which a ring shuttles along a prochiral axle, 27,28 have been amenable to external control. There have been no compact and controllable dynamic sp -carbon building blocks.…”

Chemically Induced Mismatch of Rings and Stations in [3]Rotaxanes

“…Mechanically interlocked molecules (MIMs) such as rotaxanes have gained considerable attention over the past three decades because of their intriguing structural and dynamic properties 1 , 2 and, in more recent years, for their application in key areas such as dyes, 3 ion recognition 4 and transport, 5 catalysis, 6 , 7 molecular electronics, 8 , 9 structural and functional materials, 10 − 14 molecular machines, 15 − 17 and nanomedicine. 18 …”

“…Also popular is the instance when n S > n R ( Figure 1 b); this is the case of molecular shuttles, where the translational movement of the ring between the stations can occur either randomly or under the control of physical or chemical stimuli. 1 , 2 , 4 − 6 , 8 , 9 , 14 , 16 , 18 …”