Bioinspired tetraamino-bisthiourea chiral macrocycles in catalyzing decarboxylative Mannich reactions

Copper(ii)-catalyzed enantioselective decarboxylative Mannich reaction coordinated by supramolecular organic amine cages

Using supramolecular chiral cages to create a favorable chiral environment can effectively address the limitations of traditional metal asymmetric catalysis in controlling chiral catalytically active centers. However, achieving harmonious interactions among the molecular cage, the metal, and the substrate within the cavity remains a significant challenge. To overcome this, we have designed a pyridinium-modified, chiral-diamine-functionalized cage with a distinct bowl-shaped geometry. This structure features three quaternary ammonium linkers at the base and three chiral cyclohexanediamine units positioned at the rim. Acting as a supramolecular chiral ligand, the coordination of this cage with copper salts forms an optimal chiral environment that enables an efficient decarboxylative Mannich reaction between β-ketoacids and imines, yielding a broad range of chiral β-amino carbonyl compounds. Mechanistic studies and control experiments reveal that the coordinated Cu center is responsible for the substrate grabbing and preorganization within the cavity and the free NH group contributes to the enhanced enantioselectivity through hydrogen bonds, collaboratively enhancing the overall catalytic efficiency.

Anion Recognition-Directed Supramolecular Catalysis with Functional Macrocycles and Molecular Cages

ConspectusThe development of supramolecular chemistry has provided a variety of host molecules and noncovalent tools for boosting catalytic processes, stimulating the emergence and advance of supramolecular catalysis, among which macrocyclic and cage-like compounds have attracted great attention due to their possession of an enzyme-mimetic cavity and recognition ability. While the privileged scaffolds such as crown ethers, cyclodextrins, cucurbiturils, calixarenes, and metal-coordinated cages have been widely used, their skeletons usually do not contain a directional binding site; binding and activation mainly rely on cation-associated interactions or hydrophobic effects. In this context, the recent advance of anion supramolecular chemistry has drawn our attention to developing an anion recognition-directed approach by using tailor-made functionalized macrocycles and cages. Anions are important widely existing species in both biological and chemical systems and play an important role in regulating the structure and function of enzymes. We envisioned that by taking advantage of anions, including their rich variety, diverse geometry, and multiple interaction sites, the sophisticated cooperation of multiple noncovalent interactions can be manipulated in a confined cavity for directing efficient and selective catalysis.Following this concept, we initiated our study by introducing typical thiourea H-bonding groups to design and synthesize a series of bis-thiourea macrocycles, especially chiral macrocycles, by incorporating chiral linkers. Taking advantage of the obtained strong, cooperative anion binding, a macrocycle-enabled counteranion trapping strategy was developed, which afforded greatly enhanced catalytic efficiency and excellent stereocontrol in acid-catalyzing reactions. Furthermore, inspired by sulfate-induced macrocyclic dimerization assembly, we built a substrate-induced assembly system, enabling an induced-fit cooperative activation network for efficient and enantioselective catalysis. In addition, anion recognition-driven chirality gearing with a more sophisticated trithiourea cage was revealed, which could provide a basis for implementing anion-triggered allosteric catalysis within the induced helical space. Not limited to hydrogen bonding, the emerging anion-π interactions were largely exploited. A series of triazine-based prism cages containing three V-shaped electron-deficient π-cavities were constructed, and their anion-π binding properties were studied. Based on this system, cooperative anion-π activation was established for driving highly efficient and selective catalysis, which paved a way to push anion-π interactions toward more practical and useful catalyst design.These results demonstrated that the anion-recognition direction can serve as a powerful, versatile approach for boosting highly efficient and selective supramolecular catalysis. It is feasible not only for employing exogenous anions (e.g., counteranion) as a handle but also for recognition and regulation of anionic active intermediates/transition states, from use in conventional H-bonding to emerging anion-π recognition.