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Title:
Molecular Mechanism and Solvation Effect of Supramolecular Catalysis in a Synthetic Cavitand Receptor with an Inwardly Directed Carboxylic Acid for Ring-Opening Cyclization of Epoxy Alcohols
Authors:
Lina Xu, Guoyong Fang, Junbin Tao, Zihang Ye, Sainan Xu, and Zhenyu Li
Abstract: Supramolecular catalysis has become a hot topic in chemistry. To understand the origin of supra-molecular catalysis, the catalytic mechanism of a synthetic cavitand receptor with an inwardly directed carboxylic acid for ring-opening cyclization of epoxy alcohols was investigated by performing density functional theory (DFT) calculations. The results reveal that the epoxy alcohol can be ring-opened via backside attack of the hydroxyl group to the epoxy group and cyclized in 5-exo and 6-endo modes. The carboxylic acid can catalyze the ring-opening cyclization of the epoxy alcohol through organocatalysis, since the carboxyl group can easily provide a proton to protonate the epoxy group. The synthetic cavitand receptor with an inwardly directed carboxylic acid can further catalyze the ring-opening cyclization of an epoxy alcohol through organocatalysis and supramolecular catalysis as a result of the hydrogen-bonding and C−H···π interactions formed between the receptor and substrate. Furthermore, the special structure and relative orientation of the substrate and the host can result in a good regioselectivity of supramolecular catalysis. In addition, the solvation analysis indicates that the solvation role has an effect on the supramolecular catalysis. The full solution-phase optimization of all species in the supramolecular catalytic reaction is given, and characterization of the solvation effect on the reaction barriers is also proposed. These insights into the catalytic mechanism and the solvation effect of the synthetic cavitand receptor may be applied to the design and synthesis of new and effective supramolecular catalysts.
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