Exploring the Aldol Reaction using Catalytic Antibodies and “On Water” Organocatalysts from QM/MM Calculations

Syntheses and Applications of Singh’s Catalyst

Singh’s catalyst has emerged as one of the most promising and valuable catalysts in the field of asymmetric synthesis. Since its discovery, it has proven to be one of the best organocatalysts for asymmetric direct aldol reactions, and is equally efficient in aqueous and organic media. In this Short Review, we summarize reactions utilizing Singh’s catalyst under various conditions.

1 Introduction

2 Synthesis of Singh’s Catalyst

3 Applications in Asymmetric Synthesis

4 Conclusion

Recent advances in reactions promoted by amino acids and oligopeptides

During the last 20 years, Organocatalysis has become one of the major fields of Catalysis. Herein, we provide a recent overview on reactions where the use of amino acids and peptides as the organocatalysts was employed. All aspects regarding aldol reactions, Michael reactions, epoxidation, Henry reactions and many others that are crucial for the reaction conditions and reaction mechanisms are discussed.

Manipulation of Water for Diversified Functionalization of Tetrahydro-β-carbolines (THβCs) with Indoles

Water plays a crucial role in organic synthesis. However, diversified functionalization manipulated by water is still rare and remains unexplored. Herein, we report the first water-manipulated protocol to achieve the diversified functionalization of tetrahydro-β-carbolines (THβCs) in an open flask at room temperature that exhibit a broad functional-group tolerance. More water leads to monoarylation, while less water leads to diarylation. Further one-step transformation afforded oxidized bis(indolyl)methanes, eudistomin U, and the related derivatives in satisfactory yields.

The Transition from Academia: Overcoming the Barrier to a Career in the Drug Discovery Industry

This perspective describes the transition from academic training (specifically graduate school and a postdoctoral fellowship) to a career in the pharmaceutical industry as a computational chemist. My personal journey from childhood to senior scientist is described, along with suggestions and insights into a career in the pharmaceutical industry.

Catalytic enantioselective aldol reactions

Recent developments in catalytic asymmetric aldol reactions have been summarized.

Mechanistic investigation inspired "on water" reaction for hydrobromic acid-catalyzed Friedel-Crafts-type reaction of β-naphthol and formaldehyde

The mechanism of the HBr-catalyzed Friedel-Crafts-type reaction between β-naphthol and HCHO was investigated by DFT to improve this reaction. The HBr-H₂ O co-catalyzed the preferential pathway undergoes the concerted nucleophilic addition and hydrogen shift, stepwise followed by H₂ O elimination and the CC bond formation. The origin of the high catalytic activity of HBr is ascribed to CH···Br^- and OH···Br^- interactions, which suggest that the active species is Br^- . Moreover, water molecules efficiently assist in improving the activity of Br^- . The computational results show that solvent polarity profoundly affects the activation barriers. To our delight, the activation barrier of the rate-determining step for the favored pathway in water is comparable (0.6 kcal/mol difference) with that in acetonitrile. The experimental observation further confirmed our results and demonstrated that the title reaction can be successfully achieved "on water." Therefore, we open a new efficient and green strategy for the synthesis of biphenol derivatives. © 2017 Wiley Periodicals, Inc.

The Role of Water in the Catalyst-Free Aldol Reaction of Water-Insoluble N-Methyl-2,4-thiazolidinedione with N-Methylisatin from QM/MM Monte Carlo Simulations

The role of water in the uncatalyzed aldol reaction of N-methyl-2,4-thiazolidinedione with N-methylisatin is investigated through Monte Carlo statistical mechanics simulations that utilize free energy perturbation theory and the mixed quantum mechanics and molecular mechanics (QM/MM) model with PDDG/PM3 for the QM method in "on-water" and DMSO environments. There are several conceivable orientations between thiazolidinedione and isatin in the process of C-C bond formation. However, the formation of the C-C bond takes place between the re face of isatin and the si face of (E)-enol of the thiazolidinedione to form the preferred anti-type product, which results from enhanced hydrogen-bonding interactions between water molecules and the oxygen atoms undergoing bond breakage and bond formation during the reaction. Novel insights into the effect of water on the aldol reaction are presented herein.

Can a Diels–Alder reaction be accelerated in a supersaturated solvent at room temperature?

New carbohydrate-based supersaturated solvent for superior rates and high product yields.

Structure-Activity Relationship Studies of Cyclopropenimines as Enantioselective Brønsted Base Catalysts

We recently demonstrated that chiral cyclopropenimines are viable Brønsted base catalysts in enantioselective Michael and Mannich reactions. Herein, we describe a series of structure-activity relationship studies that provide an enhanced understanding of the effectiveness of certain cyclopropenimines as enantioselective Brønsted base catalysts. These studies underscore the crucial importance of dicyclohexylamino substituents in mediating both reaction rate and enantioselectivity. In addition, an unusual catalyst CH···O interaction, which provides both ground state and transition state organization, is discussed. Cyclopropenimine stability studies have led to the identification of new catalysts with greatly improved stability. Finally, additional demonstrations of substrate scope and current limitations are provided herein.

Temperature-responsive hairy particle-supported proline for direct asymmetric aldol reaction in water

In this paper, three kinds of hairy particles with different brush structures were prepared and evaluated as chiral catalysts in the direct asymmetric aldol reaction.

Simulating chemical reactions in ionic liquids using QM/MM methodology

The use of ionic liquids as a reaction medium for chemical reactions has dramatically increased in recent years due in large part to the numerous reported advances in catalysis and organic synthesis. In some extreme cases, ionic liquids have been shown to induce mechanistic changes relative to conventional solvents. Despite the large interest in the solvents, a clear understanding of the molecular factors behind their chemical impact is largely unknown. This feature article reviews our efforts developing and applying mixed quantum and molecular mechanical (QM/MM) methodology to elucidate the microscopic details of how these solvents operate to enhance rates and alter mechanisms for industrially and academically important reactions, e.g., Diels-Alder, Kemp eliminations, nucleophilic aromatic substitutions, and β-eliminations. Explicit solvent representation provided the medium dependence of the activation barriers and atomic-level characterization of the solute-solvent interactions responsible for the experimentally observed "ionic liquid effects". Technical advances are also discussed, including a linear-scaling pairwise electrostatic interaction alternative to Ewald sums, an efficient polynomial fitting method for modeling proton transfers, and the development of a custom ionic liquid OPLS-AA force field.