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N-heterocyclic olefin (NHO) derivatives have an electron-rich as well as highly polarized carabon-carbon (C=C) double bond because of the electron-donating nature of nitrogen and sulphur atoms. While NHOs have been developing as novel organocatalysts and ligands for transition-metal complexes in various organic compound syntheses, different research groups are currently interested in preparing imidazole and triazolium-based chiral NHO catalysts. Some of them have been used for enantioselective organic transformations, but were still elusive. N-heterocyclic olefins, the alkylidene derivatives of N-heterocyclic carbenes (NHC), have shown promising results as effective promoters for numerous organic syntheses such as asymmetric catalysis, hydroborylation, hydrosilylation, reduction, CO 2 sequestration, alkylation, cycloaddition, polymerization and the ring-opening reaction of aziridine and epoxides, esterification, C-F bond functionalization, amine coupling, trifluoromethyl thiolation, amination etc. NHOs catalysts with suitable structures can serve as a novel class of Lewis/Bronsted bases with strong basicity and high nucleophilicity properties.These facts strongly suggest their enormous chemical potential as sustainable catalysts for a wide variety of reactions in synthetic chemistry. The synthesis of NHOs and their properties are briefly reviewed in this article, along with a summary of the imidazole and triazole core of NHOs' most recent catalytic uses., (© 2023 Wiley-VCH GmbH.)

Hydrogen bonding is a key molecular interaction in biological processes, drug delivery, and catalysis. This report describes a high throughput UV-Vis spectroscopic method to measure hydrogen bonding capacity using a pyrazinone sensor. This colormetric sensor reversibly binds to a hydrogen bond donor, resulting in a blue shift as additional equivalents of donor are added. Titration with excess equivalents of donor is used to determine the binding coefficient, ln(K eq ). Over 100 titrations were performed for a variety of biologically relevant compounds. This data enabled development a multiple linear regression model that is capable of predicting 95 % of ln(K eq ) values within 1 unit, allowing for the estimation of hydrogen bonding affinity from a single measurement. To show the effectiveness of the single point measurements, hydrogen bond strengths were obtained for a set of carboxylic acid bioisosteres. The values from the single point measurements were validated with full titrations., (© 2023 Wiley-VCH GmbH.)

It is clear that the field of organocatalysis is continuously expanding during the last decades. With increasing computational capacity and new techniques, computational methods have provided a more economic approach to explore different chemical systems. This review offers a broad yet concise overview of current state-of-the-art studies that have employed novel strategies for catalyst design. The evolution of the all different theoretical approaches most commonly used within organocatalysis is discussed, from the traditional approach, manual-driven, to the most recent one, machine-driven., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Urea, which has both hydrogen bond acceptor and donor moieties, is an ideal structure for a supramolecular synthon. Various supramolecules having ureido group(s) have been widely developed. This article summarizes recent developments of urea derivatives that exhibit various functions: i) supramolecular capsules that form discrete urea-urea intermolecular hydrogen bonds, ii) supramolecular polymers that form continuous urea-urea intermolecular hydrogen bonds, iii) supramolecular gels that form continuous urea-urea intermolecular hydrogen bonds, iv) artificial host molecules based on the molecular recognition ability of the ureido group, and v) catalytic reactions developed by utilizing the molecular recognition ability of the ureido group., (© 2020 Wiley-VCH GmbH.)

Selective two-electron reduction of dioxygen (O 2 ) to hydrogen peroxide (H 2 O 2 ) has been achieved by two saddle-distorted N,N'-dimethylated porphyrin isomers, an N21,N'22-dimethylated porphyrin (anti-Me 2 P) and an N21,N'23-dimethylated porphyrin (syn-Me 2 P) as catalysts and ferrocene derivatives as electron donors in the presence of protic acids in acetonitrile. The higher catalytic performance in an oxygen reduction reaction (ORR) was achieved by anti-Me 2 P with higher turnover number (TON=250 for 30 min) than that by syn-Me 2 P (TON=218 for 60 min). The reactive intermediates in the catalytic ORR were confirmed to be the corresponding isophlorins (anti-Me 2 Iph or syn-Me 2 Iph) by spectroscopic measurements. The rate-determining step in the catalytic ORRs was concluded to be proton-coupled electron-transfer reduction of O 2 with isophlorins based on kinetic analysis. The ORR rate by anti-Me 2 Iph was accelerated by external protons, judging from the dependence of the observed initial rates on acid concentrations. In contrast, no acceleration of the ORR rate with syn-Me 2 Iph by external protons was observed. The different mechanisms in the O 2 reduction by the two isomers should be derived from that of the arrangement of hydrogen bonding of a O 2 with inner NH protons of the isophlorins., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The pot-economical, highly enantioselective synthesis of axially chiral biaryls was developed by using one-pot organocatalyst-mediated domino and aromatization reactions as key steps. The axial information of the precursor, which also has central chirality, was completely inverted in the final biaryls. The inversion of the axial information occurred in the conversion of the central chirality to the axial chirality of an oxidative aromatization step., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

An organocatalytic arylation of α-ketoesters was developed on the basis of umpolung strategy. Phosphazene P2-tBu efficiently catalyzes the three-component coupling reaction of α-ketoesters, a silylated secondary phosphite, and electron-deficient fluoroarenes to provide α-hydroxyester derivatives possessing an electron-deficient aryl group at the α-position. The reaction involves the catalytic generation of α-oxygenated ester enolates from α-ketoesters through the [1,2]-phospha-Brook rearrangement followed by the S N Ar reaction., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Hydrodefluorination reactions (HDF) of per- and polyfluorinated olefins and arenes by cheap aluminum alkyl hydrides in non-coordinating solvents can be catalyzed by O and N donors. TONs with respect to the organocatalysts of up to 87 have been observed. Depending on substrate and concentration, high selectivities can be achieved. For the prototypical hexafluoropropene, however, low selectivities are observed (E/Z≈2). DFT studies show that the preferred HDF mechanism for this substrate in the presence of donor solvents proceeds from the dimer Me 4 Al 2 (μ-H) 2 ⋅THF by nucleophilic vinylic substitution (S N V)-like transition states with low selectivity and without formation of an intermediate, not via hydrometallation or σ-bond metathesis. In the absence of donor solvents, hydrometallation is preferred but this is associated with inaccessibly high activation barriers at low temperatures. Donor solvents activate the aluminum hydride bond, lower the barrier for HDF significantly, and switch the product preference from Z to E. The exact nature of the donor has only a minimal influence on the selectivity at low concentrations, as the donor is located far away from the active center in the transition states. The mechanism changes at higher donor concentrations and proceeds from Me 2 AlH⋅THF via S N V and formation of a stable intermediate, from which elimination is unselective, which results in a loss of selectivity., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A novel "umpolung" intramolecular cyclization of alkynyl imines, in which the electrophilic imine sp 2 -carbon formally serves as a nucleophilic site, was developed under Brønsted base catalysis. The reaction involves the unprecedented catalytic generation of α-aminoester enolates from α-iminoesters via the 1,2-addition of the anion of a secondary phosphite to an imine moiety followed by the [1,2]-rearrangement of a dialkoxyphosphoryl moiety from carbon to nitrogen, which is a formal umpolung process, and the intramolecular addition to an alkyne. This is a rare example of a [1,2]-rearrangement of a dialkoxyphosphoryl moiety from carbon to nitrogen to generate an α-amino carbanion and the first catalytic carbon-carbon bond forming reaction utilizing the resulting carbanion as a nucleophile., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Alkyne-based click polymerizations have been well-established. However, in order to expand the family to synthesize polymers with new structures and novel properties, new types of click polymerizations are highly demanded. In this study, for the first time, we established a new efficient and powerful phenol-yne click polymerization. The activated diynes and diphenols could be facilely polymerized in the presence of the Lewis base catalyst of 4-dimethylaminopyridine (DMAP) under mild reaction conditions. Regio- and stereoregular poly(vinylene ether ketone)s (PVEKs) with high molecular weights (up to 35 200) were obtained in excellent yields (up to 99.0 %). The reaction mechanism was well explained under the assistance of density functional theory (DFT) calculation. Furthermore, since the vinyl ether sequence acts as a stable but acid-liable linkage, the polymers could be decomposed under acid conditions, rendering them applicable in biomedical and environmental fields., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Metal-free initiating systems for living cationic polymerizations are desirable from the viewpoint of environmentally benign polymer synthesis. We describe here the development of a halogen-bonding-mediated and controlled cationic polymerization of isobutyl vinyl ether (IBVE) using 2-iodoimidazolium salts as an organocatalyst. Due to the ionic nature of the catalysts, the polymerization should be performed in CH 2 Cl 2 . The HCl-adduct of IBVE was the most suitable initiator, and the polymerization was carried out at -10 °C under the catalyst concentration of 10 mm to suppress alcohol elimination from the polymer chain. The addition of a small amount of nBu 4 NCl (0.02 equivalent) was effective to accomplish the controlled cationic polymerization and obtain polyIBVE, having the molecular weight distribution below 1.3., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The simple tetraminocalix[4]arene 1, which contains weak H-bond-donor NH 2 groups, is reported to be a highly efficient organocatalyst for the Vinylogous Mukaiyama Aldol Reaction (VMAR) of 2-(trimethylsilyloxy)furan 5 with α-ketoesters 6 a-l under "on-water" conditions owing to the hydrophobic amplification of weak H-bond interactions. The catalytic efficiency of calixarene catalyst 1 was shown to be closely related to its recognition abilities towards the reactants 5 and 6 through a multipoint recognition model. The proposed model provided good explanations for the differences on the reaction rate acceleration and on the stereoselectivity observed with different substrates., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The control of stereoselectivity in radical reactions is of great importance to organic synthesis. Hence, new concepts and strategies for controlling stereochemistry of radical reactions are emerging continuously. This Review highlights the recent remarkable progress in enantioselective radical cyclization reactions. Initially, the chiral Lewis acid-catalyzed method became a field of central importance for enantioselective radical cyclizations. In recent years, significant progress has been made in enantioselective organocatalysis. In contrast to intermolecular reactions, the successful examples for enantioselective radical cyclizations are still limited. In this Review, the radical cyclizations controlled by chiral Lewis acids, chiral metallic reagents, chiral imidazolidinone catalysts, chiral non-covalent organocatalysts, and chiral thiols are summarized., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Given the important agricultural and medicinal application of optically pure heterocycles bearing a trifluoromethyl group at the stereogenic carbon center in the heterocyclic framework, the exploration of efficient and practical synthetic strategies to such types of molecules remains highly desirable. Catalytic enantioselective synthesis has one clear advantage that it is more cost-effective than other synthetic methods, but remains limited by challenges in achieving excellent yield and stereoselectivities with a low catalyst loading. Thus far, numerous models of organo- and organometal-catalyzed asymmetric reactions have been exploited to achieve this elusive goal over the past decade. This review article describes recent progress on this research topic, and focuses on an understanding of the catalytic asymmetric protocols exemplified in the catalytic enantioselective synthesis of a wide range of complex enantioenriched trifluoromethylated heterocycles., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Go organic! N-Heterocyclic carbene (NHC) 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (IiPr) has been found to be an efficient and selective catalyst for the dehydrogenative coupling of a wide range of silanes and hydroxyl groups to form SiO bonds under mild and solvent-free conditions. Mechanistic studies indicated that the activation of hydroxyl groups by the NHC is the most plausible initial step for the process., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)