Dynamic Control of Chiral Space Through Local Symmetry Breaking in a Rotaxane Organocatalyst. Issue 42 (10th September 2019)

• Record Type: Journal Article
• Authors: Dommaschk, Marcel; Echavarren, Javier; Leigh, David A.; Marcos, Vanesa; Singleton, Thomas A.
• Is Part Of: Angewandte Chemie international edition. Volume 58:Issue 42(2019)
• Page Start: 14955
• Page End: 14958
• Publication Date: 2019-09-10
• Subjects: asymmetric catalysis -- chirality -- molecular machines -- rotaxanes -- switchable catalysts; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.201908330
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: We report on a switchable rotaxane molecular shuttle that features a pseudo‐ meso 2, 5‐disubstituted pyrrolidine catalytic unit on the axle whose local symmetry is broken according to the position of a threaded benzylic amide macrocycle. The 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 a catalyst (2–14 % ee ), whereas the rotaxane affords selectivities of up to 40 % ee with switching of the position of the macrocycle changing the handedness of the product formed (up to 60 % Δee). Abstract : Changing hands : The stimuli‐induced change of macrocycle position in a rotaxane is exploited to switch the effective handedness of a catalytic center on the axle. The dynamic switching is used to reverse the enantioselectivity of an enamine‐mediated conjugate addition.