Task-Specific Design of a Porous Aromatic Framework as an Ultrastable Platform for Enantioselective Organocatalysis

A hydroxyl-tagged porous aromatic framework PAF-NBU2-OH was task-specifically designed and successfully synthesized targeted toward immobilizing chiral catalysts. Using proline-type compound as model chiral organocatalyst, PAF-NBU2-OH was used as a platform to covalently link proline-type group. The obtained PAF-immobilized organocatalyst PAF-NBU2-OPro featured high chemical stability in different solvents even under very harsh conditions. PAF-NBU2-OPro showed excellent catalytic activity, diastereoselectivity and enantioselectivity with complete and easy recyclability when catalyzing the aldol reaction between p-nitrobenzaldehyde and cyclohexanone, which could undergo at least 30 cycles without any activity, diastereoselectivity or enantioselectivity loss for catalyzing the current reaction.

Precise Synthesis of Diastereomers of Spiro-oxindole Derivatives through Dynamic Covalent Transformation

In this study, [1+2+2] cyclization of tryptamine-derived isocyanides with 3-ylideneoxindoles was systematically investigated. A series of structurally complex spiro-oxindole derivatives were obtained. Characteristic dynamic covalent chemistry was observed and confirmed by experiments and density functional theory calculation. Through the regulation of the solvent, temperature, and time, the precise and stereodivergent synthesis of spiro-oxindoles was achieved.

Diastereoselective reversible C-C bond exchange of oxindole-thiazolidienediones for dynamic combinatorial chemistry

We herein describe a diastereoselective aldol exchange involving isatins and thiazolidinediones, providing oxindolyl-thiazolidienediones in aqueous media at pH 6. This equilibrium can also be achieved with oxindole exchange as well as cross-exchange within reasonable timescales. These metal and organic catalyst free reversible reactions provide a unique opportunity for the evolution of dynamic combinatorial libraries (DCLs) for target directed dynamic combinatorial chemistry (DCC) and system chemistry.

Designed from Biobased for Recycling: Imine-Based Covalent Adaptable Networks

Turning thermosets into fully sustainable materials requires utilization of biobased raw materials and design for easy recyclability. Here, dynamic covalent chemistry for fabrication of covalent adaptable networks (CANs) could be an enabling tool. CAN thermosets ideally combine the positive material properties of thermosets with thermal recyclability of linear thermoplastics. Among the dynamic covalent bonds, imine bond, also called Schiff base, can participate in both dissociative and associative pathways. This induces potential for chemical recyclability, thermal reprocessability and self-healing. This review presents an overview of the current research front of biobased thermosets fabricated by Schiff base chemistry. The discussed materials are categorized on the basis of the employed biobased components. The chemical approaches for the synthesis and curing of the resins, as well as the resulting properties and recyclability of the obtained thermosets are described and discussed. Finally, challenges and future perspectives are briefly summarized. This article is protected by copyright. All rights reserved.

Dynamic Catalytic Highly Enantioselective 1,3-Dipolar Cycloadditions

In dynamic covalent chemistry, reactions follow a thermodynamically controlled pathway through equilibria. Reversible covalent‐bond formation and breaking in a dynamic process enables the interconversion of products formed under kinetic control to thermodynamically more stable isomers. Notably, enantioselective catalysis of dynamic transformations has not been reported and applied in complex molecule synthesis. We describe the discovery of dynamic covalent enantioselective metal‐complex‐catalyzed 1,3‐dipolar cycloaddition reactions. We have developed a stereodivergent tandem synthesis of structurally and stereochemically complex molecules that generates eight stereocenters with high diastereo‐ and enantioselectivity through asymmetric reversible bond formation in a dynamic process in two consecutive Ag‐catalyzed 1,3‐dipolar cycloadditions of azomethine ylides with electron‐poor olefins. Time‐dependent reversible dynamic covalent‐bond formation gives enantiodivergent and diastereodivergent access to structurally complex double cycloadducts with high selectivity from a common set of reagents.

Asymmetric Synthesis of Substituted Thiolanes through Domino Thia-Michael-Henry Dynamic Covalent Systemic Resolution using Lipase Catalysis

Dynamic systems based on consecutive thia-Michael and Henry reactions were generated and transformed using lipase-catalyzed asymmetric transformation. Substituted thiolane structures with three contiguous stereocenters were resolved in the process in high yields and high enantiomeric excesses.

Recent advances in dynamic covalent chemistry

Dynamic covalent chemistry (DCvC) has been strongly integrated into diverse research fields, and has enabled easy access to a variety of combinatorial libraries, 2-D macrocycles, and 3-D molecular cages that target many important applications, such as drug discovery, biotechnology, molecular separation, light harvesting, etc. DCvC relies on the reversible formation and breaking of rather strong covalent bonding within molecules. Therefore it combines the error-correction capability of supramolecular chemistry and the robustness of covalent bonding. Compared to those supramolecular interactions, dynamic covalent reactions usually have slower kinetics and require the assistance of catalysts to achieve rapid equilibrium. Although the scope of dynamic covalent reactions is rapidly expanding, the reversible reactions suitable for DCvC are still very limited. The identification and development of new dynamic reactions and catalysts would be critical for the further advancement of DCvC. This review covers the recent development of dynamic covalent reactions as well as their applications.

Silver-catalyzed dynamic systemic resolution of α-iminonitriles in a 1,3-dipolar cycloaddition process

A silver-catalyzed dynamic azomethine ylide system was kinetically resolved in a tandem cycloaddition process, yielding an exclusive pyrrolidine product.