Lukas Kell

Color is central to scientific communication, but its use comes with the responsibility to ensure universally accessible and accurate data presentation. This short Viewpoint Article aims to sensitize the chemical community to the importance of mindful color choices in scientific illustrations.

Abstract

Color is a central element to scientific communication, but its use comes with the responsibility to ensure universally accessible and accurate data presentation. This short Viewpoint Article aims to sensitize the chemical community to the importance of mindful color choices in scientific illustrations.

Synthesis
DOI: 10.1055/a-1736-6703

Design of Experiments (DoE) is extensively and routinely used in industry; however, in recent decades, it has gained increasing interest from academia in organic synthesis. The use of chemometrics is an attractive strategy to find the real optimum in chemical reactions, especially when affected by several variables. DoE has been applied in a growing number of synthetic transformations over the years, where it undoubtedly helps in the process of optimisation, saving costs and time. This review concisely discusses the chemometric basis of Design of Experiments and highlights several examples in which DoE is applied in organic synthesis.1 Introduction2 Chemometric Basis of DoE3 DoE Applied in Catalysis: Selected Examples3.1 DoE in Metal Catalysis3.2 DoE in Biocatalysis3.3 DoE in Organocatalysis4 Conclusions
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Article in Thieme eJournals:
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You can play Pac Man with Phosphorus! The first non-metal Pacman compound, a calix[4]pyrrole schiff base ligand coordinating two highly dynamic P^(III)Cl moieties is presented. Chloride abstraction with AgOTf leads to a macrocyclic dication with two embedded phosphorus monocations, both of which undergo a cooperative internal activation reaction.

Abstract

Formal coordination of phosphorus(III) by a calix[4]pyrrole Schiff base ligand was achieved through the reaction of this ligand with PCl₃ under basic conditions. The reaction product adopts a Pacman conformation with two P−Cl moieties, one in exo and one in endo position. It represents the first non-metal compound of calix[4]pyrrole Schiff base ligands and of Pacman ligands in general. The spatial neighborhood of the two phosphorus atoms enables cooperative reactions. As a first example, the chloride abstraction with AgOTf is presented, yielding a macrocyclic dication with two embedded phosphorus(III) monocations, which both undergo a cooperative, internal activation reaction with an adjacent C=N double bond. This intramolecular redox process affords two pentacoordinated phosphorus(V) centers within the Pacman dication. All reaction products were fully characterized and all results are supported by computations.

“I chose chemistry as a career because I liked the endless connections of different disciplines within chemistry … My favorite piece of research is the early study of antiseptic procedures by Ignác Fülöp Semmelweis …” Find out more about Eszter Baráth in her Introducing … Profile.

Cascade reactions, either induced by halogenation or involving halogenated synthetic building blocks, have been utilized in recent years to obtain a variety of cyclic compounds, of interest for many applications. In this review the literature on enantioselective catalytic methods of synthesis is surveyed for the period 2014–2020.

Abstract

Chiral halogenated substances have many applications in pharmaceuticals, agrochemicals, and materials, such as polymers, liquid crystals and as intermediates in synthesis. The presence of a halogen atom in a molecule can have a large effect in its properties; for instance, halogens are used in drugs to improve lipophilicity, membrane permeability and absorption, and even the blood-brain barrier permeability. As highlighted in this review, there are nowadays a range of highly selective, versatile halogenating reagents, electrophilic, nucleophilic or radical in nature, which operate under mild conditions, allowing late-stage functionalization of complex molecules in cascade reactions. Recent developments in organocatalyst design revealed novel Cinchona alkaloids derivatives, chiral phosphoric acids, amines, phosphines and several bifunctional catalysts, mostly thiourea- or squaramide-based, which introduced chirality, with high levels of enantio- and diastereoselection, in the formation of one or multiple chiral centers in a single synthetic operation, as shown. In this review we survey the literature published in this field from 2014 to 2020.

Nature, Published online: 01 June 2021; doi:10.1038/d41586-021-01431-y

The corresponding in‐depth analysis shows the general and extensive applicability of the MFR concept with an immobilized L‐proline‐based catalyst for carrying out asymmetric aldol reactions with various substrates. Using cyclohexanone and cyclopentanone as well as acetone, various ketones could be successfully converted as donors in the aldol reaction with various substituted aldehydes.

Abstract

Continuous flow catalysis using a microfluidic reactor with gel‐bound proline organocatalysts is an attractive approach in organic synthesis due to interesting advantages such as the permanent production of catalyst‐free products and the easy product isolation by evaporation. Further advantages are the online detection of reactions and an adjustment of reaction parameters while the reaction is already running. Herein the formation of differently substituted aldol products within minutes at mild conditions in good to almost quantitative yields is described. The effects of different solvent mixtures and temperatures on the conversion and selectivity are analyzed in detail by NMR as well as the relationship between the height of the polymer structures and the conversion behavior of the asymmetric aldol reaction of 4‐nitrobenzaldehyde and cyclohexanone. The applicability of this system is demonstrated for a wide range of differently substituted nitrobenzaldehydes. It is shown that the described reactor setup delivers high conversion and good selectivity over up to 144 hours and that a highly reusable system was established.

Enantioselective catalysis using organocatalysts is a highly desirable process for the synthesis of organic molecules in an enantioenriched form. This minireview highlights recent achievements in the development of enantioconvergent substitution reactions of racemic electrophiles using organocatalysts. The contents are classified on the basis of the mechanistic types of enantioconvergent processes.

Abstract

Over the past decades, the development of enantioselective catalysis using organocatalysts has evolved into an active research field and a number of enantioselective transformations have been established. However, despite their being a highly desirable process for the synthesis of organic molecules in an enantioenriched form, the enantioconvergent substitution reactions of racemic electrophiles using organocatalysts still present several challenges. Although intrinsic difficulties in the catalytic stereocontrol abound due to the initial chiral information of racemic electrophiles, in recent years, mechanistically diverse enantioconvergent processes have been intensively investigated in organocatalysis. This Minireview focuses on recent achievements in the development of enantioconvergent substitution reactions of racemic electrophiles using organocatalysts. The contents are classified on the basis of the mechanistic types of enantioconvergent processes.