Asymmetric catalysis mediated by a mirror symmetry-broken helical nanoribbon

Abstract

Although chirality has been recognized as an essential entity for life, it still remains a big mystery how the homochirality in nature emerged in essential biomolecules. Certain achiral motifs are known to assemble into chiral nanostructures. In rare cases, their absolute geometries are enantiomerically biased by mirror symmetry breaking. Here we report the first example of asymmetric catalysis by using a mirror symmetry-broken helical nanoribbon as the ligand. We obtain this helical nanoribbon from a benzoic acid appended achiral benzene-1,3,5-tricarboxamide by its helical supramolecular assembly and employ it for the Cu 2+ -catalyzed Diels–Alder reaction. By thorough optimization of the reaction (conversion: > 99%, turnover number: ~90), the enantiomeric excess eventually reaches 46% (major/minor enantiomers = 73/27). We also confirm that the helical nanoribbon indeed carries helically twisted binding sites for Cu 2+ . Our achievement may provide the fundamental breakthrough for producing optically active molecules from a mixture of totally achiral motifs.

Supramolecular Polymers – we've Come Full Circle

“…Using achiral GPC, these polymers are separated and hence enantiomers are separated. In a recent review, Sanchez described many more important examples of C3‐symmetrical π‐scaffolds as useful building blocks to construct helical supramolecular polymers . This review includes the triphenylamine‐based building blocks as introduced and studied in detail by Giuseppone, which was recently reviewed as well …”

Higher-order interfiber interactions in the self-assembly of benzene-1,3,5-tricarboxamide-based peptides in water

“…28,29 Furthermore, several studies have reported the formation of more complicated structures (e.g., nanoribbons or triple helices) during the self-assembly of BTAbased molecules in organic solvents or their mixtures with water. [30][31][32] In water, stepwise self-assembly into clearly defined double helical nanorods was reported only for BTA-based Aucontaining metalloamphiphiles. 33 Additionally, bundles with an order higher than double helices only formed from BTA-based molecules in aqueous solution as metastable intermediates.…”

Effect of Stereochemistry on Chirality and Gelation Properties of Supramolecular Self‐Assemblies

“…Usually, chiral molecular units can decide both molecular conformations and supramolecular biological functions [5, 6] . Inspired by the specific chirality in processes related to life, the design and fabrication of chiral nanostructures, as well as their applications in the fields of asymmetric catalysis, [7, 8] enantiomer discrimination, or sensors, [9, 10] biological effects [11, 12] and optical materials [13] have been reported in great numbers. However, the establishment of clear rules for achieving accurate knowledge about chiral amplification in self‐assembling systems is still challenging [14–17] .…”