C-O bond cleavage of allylic alkyl ether was realized in a Pd-catalyzed hydrogen-bond-activated allylic alkylation using only alcohol solvents. This procedure does not require any additives and proceeds with high regioselectivity. The applicability of this transformation to a variety of functionalized allylic ether substrates was also investigated. Furthermore, this methodology can be easily extended to the asymmetric synthesis of enantiopure products (99% ee).

Benzene hydrogenation is an important industrial process. The reaction is incomplete, resulting in a mixture of benzene, cyclohexane, and/or cyclohexene that have to be separated before any further reactions. The currently used extractive and azeotropic distillations are operationally complex and energy intensive. Adsorptive separation provides an alternative energy-efficient method. However, the separation of the ternary mixture by adsorptive separation has not yet been reported. In the present research, we report two macrocyclic hosts with hydrogen-bonding sites in their cavities that are able to separate the ternary mixture of benzene, cyclohexene, and cyclohexane. NÀH•••p interactions were found to play a key role in the selective separation. In addition, fast adsorption, high loading ratios, and easy recycling are achieved with the present system, which is promising for practical applications.

Optical methods are promising to address the ever‐increasing demands for chirality analysis in drug discovery and related fields because they are amenable to high‐throughput screening. Circular dichroism‐based chiroptical sensing using host‐guest chemistry is especially appealing due to the fast equilibrium kinetics, wide substrate scope, and potential for sustainable development. In this Minireview, we give an overview on this emerging field. General aspects of molecular recognition and chirality transfer are analyzed. Chirality sensors are discussed by dividing them into three classes according to their structural features. Applications of these chirality sensors for chirality analysis of the products of asymmetric reactions and for the real‐time monitoring of reaction kinetics are demonstrated with selected examples. Moreover, challenges and research directions in this field are also highlighted.

Optical chirality sensing has attracted a lot of interest due to its potential in high‐throughput screening in chirality analysis. A molecular sensor is required to convert the chirality of analytes into optical signals. Although many molecular sensors have been reported, sensors with wide substrate scope remain to be developed. Herein, we report that the amide naphthotube‐based chirality sensors have an unprecedented wide scope for chiroptical sensing of organic molecules. The substrates include, but are not limited to common organic products in asymmetric catalysis, chiral molecules with inert groups or remote functional groups from their chiral centers, natural products and their derivatives, and chiral drugs. The effective chirality sensing is based on biomimetic recognition in water and on effective chirality transfer through guest‐induced formation of a chiral conformation of the sensors. Furthermore, the sensors can be used in real‐time monitoring on reaction kinetics in water and in determining absolute configurations and ee values of the products in asymmetric catalysis.

Induced fit and conformational selection are two dominant binding mechanisms in biology. Although induced fit has been widely accepted by supramolecular chemists, conformational selection is rarely studied with synthetic systems. In the present research, we report a macrocyclic host whose binding mechanism is unambiguously assigned to conformational selection. The kinetic and thermodynamic aspects of this system are studied in great detail. It reveals that the kinetic equation commonly used for conformational selection is strictly followed here. In addition, two mathematical models are developed to determine the association constants of the same guest to the two host conformations. A “conformational selectivity factor” is defined to quantify the fidelity of conformational selection. Many details about the kinetic and thermodynamic aspects of conformational selection are revealed by this synthetic system. The conclusion and the mathematical models reported here should be helpful in understanding complex molecular recognition in both biological and synthetic systems.

Enantioselective recognition in water remains an ongoing challenge in supramolecular chemistry but is routine in nature. Herein, we report the first enantiopure pair of biomimetic macrocyclic receptors with hydrogen bonding donors in their deep hydrophobic cavities. The chiral naphthotubes can be efficiently synthesized through a chirality-directed macrocyclization strategy and are able to discriminate the enantiomers of neutral chiral molecules in water. Density functional theory calculations reveal that the "three-point contact" model effectively explains their enantioselectivity. The differential noncovalent interactions inside the hydrophobic cavity are responsible for the enantioselective recognition. Moreover, these chiral naphthotubes are both fluorescent and circular dichroism (CD)-active. In CD spectroscopy, they have been demonstrated to have the ability to detect nonchromophoric, achiral molecules in water. And, the use of fluorescence spectroscopy has aided in the determination of the enantiomeric excess (ee) values of chiral molecules. The results and conclusions obtained with these chiral biomimetic receptors can be used to better understand enantioselective recognition in biological systems.

Buried salt bridges widely exist in protein structures but are rarely used in synthetic systems for molecular recognition in water.B ym imicking the binding pocket of bioreceptors,w ed esigned and synthesized ap air of endofunctionalizedm acrocyclic hosts with secondary ammonium groups in ah ydrophobic cavity.W ef ound that these macrocycles are able to selectively recognizecarboxylic acids in water through salt bridges and the hydrophobic effect. Moreover,i t was demonstrated that these macrocyclic receptors can be used in circular-dichroism-based optical chirality sensing of chiral carboxylic acids and fluorescent sensing of phenylpyruvic acid-a biomarker for phenylketonuria. This researchs howcases that buried salt bridges can be effectively used by endofunctionalizedm acrocyclic hosts for molecular recognition in water,w here solvent screening on polar noncovalent interactions is high.

Chiral allylic amines are not only present in many bioactive compounds, but can also be readily transformed to other chiral amines. Therefore, the asymmetric synthesis of chiral allylic amines is highly desired. Herein, we report two types of Ni(II)-catalyzed asymmetric alkenylation of cyclic ketimines for the preparation of chiral allylic amines. When ketimines bear alkyl or alkoxycarbonyl groups, the alkenylation gives five- and six-membered cyclic α-tertiary allylic amine products with excellent yields and enantioselectivities under mild reaction conditions. A variety of ketimines can be used and the method tolerates some variation in alkenylboronic acid scope. Furthermore, with alkenyl five-membered ketimine substrates, an alkenylation/rearrangement reaction occurs, providing seven-membered chiral sulfamide products bearing a conjugated diene skeleton with excellent yields and enantioselectivities. Mechanistic studies reveal that the ring expansion step is a stereospecific site-selective process, which can be catalyzed by acid (Lewis acid or Brønsted acid).