An efficient amination reaction of 3-substituted benzofuran-2(3H)-ones promoted by cesium carbonate was developed. A putative mechanism involving a single-electron-transfer event was proposed, which represents a new reactivity for benzofuran-2(3H)-ones.

Equilibrium acidities of proline and its derived organocatalysts were measured in DMSO by an overlapping indicator method via UV/vis spectrophotometric titration. The pKa values are in the range of 11.17–23.81.

A highly enantioselective [4 + 2] cycloaddition of allenoates with 2-olefinic benzofuran-3-ones catalyzed by (DHQD)2AQN, which allowed the synthesis of optically active dihydropyran-fused benzofurans, was developed.

In contrast to the great success of computational methodologies in molecular solvents, effective and accurate calculation of the fundamental bond energetic properties in ionic liquids (ILs) is essentially absent. This is largely due to the unusual complexity of handling solvation quantities of ILs and the lack of precisely determined bond parameters to serve as the authentic benchmark to calibrate the modeling methodology. Herein, we report the first accurate calculations of absolute pKa values in a commonly used IL, [Bmim][NTf2], with the carefully developed “ion-biased” cluster-continuum model. Experimental pKa values of benzoic acids and benzenethiols in [Bmim][NTf2] were reproduced with mean unsigned errors of only 0.3 and 0.5 pKa units, respectively, which enables theoretical approaches with a suitable strategy as a powerful tool to handle complicated problems in ILs and to eventually realize the rational design of the IL chemistry.

A number of popular squaramide organocatalysts’ acidities were determined by an overlapping indicator method in DMSO via UV spectrophotometric titrations. The pKa values are in the range of 8.37–16.46. The results may be helpful for the rational design and development of squaramide type new catalysts.

The pKa values of a series of chiral Brønsted acids, including N-triflylphosphoramides, bis(sulfonyl)imides, bis(sulfuryl)imides, dicarboxylic acids, sulfonic acids, and N-phosphinyl phosphoramides, were predicted by using the SMD/M06-2x/6-311++G(2df,2p)//B3LYP/6-31+G(d) method in DMSO. The results revealed that the calculated pKa values ranged from −9.06 to 12.18 for different types of acids. The influence of acidic strength on reactivity and stereoselectivity was discussed using the calculated acidity data. Given that the choice of catalyst with appropriate acidity is the primary condition, several new catalyst candidates were designed by calculating corresponding pKa values of parent acids.

The pKa shifts of proline induced by a family of hydrogen-bond-donating cocatalysts were computationally evaluated with the M06-2x/6-311++G(2df, 2p)//B3LYP/6-31+G(d)(SMD) method. The calculation predicted that the acidity of proline could be increased by more than 9 pKa units in nonpolar solvents (n-hexane and toluene) when it assembles with hydrogen-bond-donating cocatalysts, which would contribute to the dramatically enhanced catalytic properties. For hydrogen-bond-donating cocatalysts, their relative abilities to induce the pKa shifts of proline in the gas phase and common organic solvents were established and were found to be well-correlated with their acidities. The results may aid in future development of modularly designed supramolecular catalysis—the assembly of catalyst species by harnessing multiple weak intermolecular interactions.

A highly enantioselective Michael–aldol tandem reaction with respect to prochiral 2-substituted benzofuran-3-ones and enones by a facile primary amine catalyst was investigated. The approach provides rapid access to the desired pharmaceutically active griseofulvin analogues.

Equilibrium acidity (pKa) scales of 15 substituted benzoic acids in four room temperature ionic liquids (RTILs), BmimOTf, BmimNTf2, BmpyNTf2, and Bm2imNTf2, were established under standard conditions using a modified indicator overlapping method. The effect of homo hydrogen bonding on equilibrium acidity was calibrated, and the derived pKa values were evidenced to be free from ion-paring complication. Regression analyses demonstrated that all of the pKa scales obtained in four RTILs are linearly correlated to each other with an R value better than 0.996. These scales are also correlated well with the pKa values in DMSO and with the corresponding gas-phase acidities with regression coefficients of 0.993 and 0.992, respectively. In addition, both the cation and anion of the ionic liquids were found to play a role in affecting the acidity of carboxylic acid.

The pKa values of 41 chiral phosphoric acid-family catalysts in DMSO were predicted using the SMD/M06-2x/6-311++G(2df,2p)//B3LYP/6-31+G(d) method for the first time. The study showed that the calculated pKa’s range from −4.23 to 6.16 for absolute pKa values and from −4.21 to 6.38 for relative pKa values. Excellent agreement between the calculated and experimental pKa’s was achieved for the few available cases (to a precision of around 0.4 pKa unit), indicating that this strategy may be suitable for calculating highly accurate pKa’s. A good linear correlation between the pKa’s for 3 and 3′ disubstituted phenyl BINOL phosphoric acids and the Hammett constants was obtained. The relationship between the acidities of phosphoric acid catalysts and their reaction activity and selectivity was also discussed. Knowledge of the pKa values of phosphoric acids should be of great value for the understanding of chiral Brønsted acid-catalyzed reactions and may aid in future catalyst design.

Energetics of bond dissociation, especially the R–H bond heterolysis free energy (pKa), has played a central role in promoting chemistry to become a rational science. Despite the oceans of acidity studies in the literature, the current knowledge is limited to that in the classical molecular solvents and is unable to be extended to anticipate the acidity changes in ionic media. As the latter is now very popular for replacing volatile organic solvents, it becomes highly desirable to know how the driving force of bond cleavage is varied as the medium composition is switched from neutral molecules to the charged ions. Here we describe a general approach to measure absolute pKa’s in pure ionic liquid (IL). The standard conditions warranting accurate measurement were outlined. The pKa’s of the selected 18 C–H type indicator acids in four ILs were determined and a convenient indicator platform was constructed for easy expansion of acidity scales. These absolute pKa’s make possible, for the first time, direct comparisons of bond energies in IL with those in molecular solvent and in the gas phase and should be able to serve as the standard parameters for calibrating computational methods suitable for the studies in ionic media. The effect of cation and anion in IL in relation to structure was analyzed.

The first set of experimentally determined C−NO bond homolytic and heterolytic dissociation enthalpies in solution is derived by using direct titration calorimetry combined with appropriate electrode potentials through thermodynamic cycles. The homolytic bond dissociation energy scale (BDEs) of the corresponding C−NO bonds in the gas phase was also calculated at the MP2/6-311+G**//B3LYP/6-31G* level and BP86/6-31G*//B3LYP/6-31G* level of theory for the purpose of comparison. The C−NO and S−NO bond thermodynamic parameters were used to predict the trend of NO transfer from C-nitroso substrates to thiols in acetonitrile solution.

The nucleophilic nature of cyanide is used to create a simple, sensitive, and highly effective sensor, 2-(trifluoroacetylamino)anthraquinone 2 (2-TFAQ), for the easy “naked-eye” detection of very low concentrations of cyanide in an aqueous environment.

A series of structurally novel anion receptors 3, 4, and 5 in which a ferrocene unit and a fluorescent moiety are linked to two imidazolium rings have been designed and prepared from 1,1′-bis(imidazolylmethyl)ferrocene. Their crystal structures revealed that these receptors are capable of incorporating anions such as PF6− and Br−. Consequently, the anion binding studies were carried out using various techniques including electrochemistry (CV and OSWV), fluorescence, UV-vis, and 1H NMR spectroscopy. All the receptors showed a special electrochemical response to the F− anion with a remarkable cathodic shift of more than 260 mV and displayed a unique selectivity for F− and AcO− anions with fluorescence enhancement over various other anions of present interest (Cl−, Br−, I−, HSO4−, H2PO4−). In addition, for receptor 5, obvious absorption changes were observed when the H2PO4− anion was added while other anions (F−, Cl−, Br−, I−, AcO−, HSO4−) showed only a minor influence on the UV-vis spectra. 1H NMR titrations demonstrated that receptors 3 and 4 can bind anions through (C–H)+⋯X−hydrogen bonds and showed strong affinity and high selectivity for the AcO− anion in acetonitrile.

A new calix[4]pyrrole type anion receptor (1) containing two anti-symmetrically meso-situated acenaphthenequinone moieties has been constructed by a “one-pot” facile synthesis. The crystal structures of 1 and 1·F− complex were characterized by X-ray crystallography. The crystal of 1·F− complex witnessed that a CH group from the acenaphthenequinone participated in anion binding through CH…F hydrogen bond which was also conformed in solution by 1H NMR titration in CD2Cl2. The anion binding property of 1 was studied in CH2Cl2 using UV–vis spectrometry and the results reflected that it bound selectively with F− and Cl− ions.

A [n]catenane supramolecular structure has been constructed by combination of metal-directed self-assembly with interligand hydrogen bonds which were confirmed by H NMR and DFT calculation.

A [n]catenane supramolecular structure has been constructed by combination of metal-directed self-assembly with interligand hydrogen bonds which were confirmed by H NMR and DFT calculation.

The nucleophilic nature of cyanide is used to create a simple, sensitive, and highly effective sensor, 2-(trifluoroacetylamino)anthraquinone 2 (2-TFAQ), for the easy “naked-eye” detection of very low concentrations of cyanide in an aqueous environment.

A series of structurally novel anion receptors 3, 4, and 5 in which a ferrocene unit and a fluorescent moiety are linked to two imidazolium rings have been designed and prepared from 1,1′-bis(imidazolylmethyl)ferrocene. Their crystal structures revealed that these receptors are capable of incorporating anions such as PF6− and Br−. Consequently, the anion binding studies were carried out using various techniques including electrochemistry (CV and OSWV), fluorescence, UV-vis, and 1H NMR spectroscopy. All the receptors showed a special electrochemical response to the F− anion with a remarkable cathodic shift of more than 260 mV and displayed a unique selectivity for F− and AcO− anions with fluorescence enhancement over various other anions of present interest (Cl−, Br−, I−, HSO4−, H2PO4−). In addition, for receptor 5, obvious absorption changes were observed when the H2PO4− anion was added while other anions (F−, Cl−, Br−, I−, AcO−, HSO4−) showed only a minor influence on the UV-vis spectra. 1H NMR titrations demonstrated that receptors 3 and 4 can bind anions through (C–H)+⋯X−hydrogen bonds and showed strong affinity and high selectivity for the AcO− anion in acetonitrile.