Hemicucurbit[6]uril-induced aerobic oxidation of heterocyclic compounds

•An aerobic oxidation of heterocyclic compounds with HemiQ[6] has been developed.•The supramolecular catalysis has been improved by protonation.•The heterocyclic compounds have been oxidized regioselectively.

The aerobic oxidation of furan in aqueous solution in the presence of HemiQ[6] has been investigated, and the product furan-2,5-diol is stabilized by encapsulation of HemiQ[6], which could be transformed to the dione confirmation in acidic solution and escape from the macrocyclic compound. The 1H NMR titration experiments of the host–guest interaction at different pH values suggest protonation should improve the encapsulation, and therefore an unique property that HemiQ[6] can be protonated has been revealed. The oxidizing kinetics suggests that the procedure is a consecutive reaction with a series of constants k1 = 2.9 × 10−2 min−1, k2 = 2.7 × 10−2 min−1, and k3 = 5.7 × 10−3 min−1, respectively. The kinetic investigation at pD = 2.0 indicates the HemiQ[6]-catalytic oxidation of furan could be accelerated by acidification. As a consequence, a plausible mechanism has been established on the above evidences. 2-Methylfuran is employed to give the product 2-methylfuran-5-ol exhibiting a satisfied activity in this aerobic oxidation with the supramolecular catalysis of HemiQ[6], but the oxidation of thiophene is very slow in either neutral or acidic condition.

Graphical abstractThe aerobic oxidation of heterocyclic compounds in aqueous solution in the presence of HemiQ[6] has been developed, and a plausible mechanism has been established. The supramolecular catalysis has been improved by protonation of the HemiQ[6].Figure optionsDownload full-size imageDownload high-quality image (94 K)Download as PowerPoint slide