The aim of this critical review is to provide a broad but digestible overview of mechanochemical synthesis, i.e. reactions conducted by grinding solid reactants together with no or minimal solvent. Although mechanochemistry has historically been a sideline approach to synthesis it may soon move into the mainstream because it is increasingly apparent that it can be practical, and even advantageous, and because of the opportunities it provides for developing more sustainable methods. Concentrating on recent advances, this article covers industrial aspects, inorganic materials, organic synthesis, cocrystallisation, pharmaceutical aspects, metal complexes (including metal–organic frameworks), supramolecular aspects and characterization methods. The historical development, mechanistic aspects, limitations and opportunities are also discussed (314 references).

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Mechanochemistry: opportunities for new and cleaner synthesis

Since the discovery of organic azides by Peter Griess more than 140 years ago, numerous syntheses of these energy-rich molecules have been developed. In more recent times in particular, completely new perspectives have been developed for their use in peptide chemistry, combinatorial chemistry, and heterocyclic synthesis. Organic azides have assumed an important position at the interface between chemistry, biology, medicine, and materials science. In this Review, the fundamental characteristics of azide chemistry and current developments are presented. The focus will be placed on cycloadditions (Huisgen reaction), aza ylide chemistry, and the synthesis of heterocycles. Further reactions such as the aza-Wittig reaction, the Sundberg rearrangement, the Staudinger ligation, the Boyer and Boyer-Aube rearrangements, the Curtius rearrangement, the Schmidt rearrangement, and the Hemetsberger rearrangement bear witness to the versatility of modern azide chemistry.

Organic Azides: An Exploding Diversity of a Unique Class of Compounds

: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Complete Field Guide to Asymmetric BINOL-Phosphate Derived Brønsted Acid and Metal Catalysis: History and Classification by Mode of Activation; Brønsted Acidity, Hydrogen Bonding, Ion Pairing, and Metal Phosphates

Flow chemistry involves the use of channels or tubing to conduct a reaction in a continuous stream rather than in a flask Flow equipment provides chemists with unique control over reaction parameters enhancing reactivity or in some cases enabling new reactions This relatively young technology has received a remarkable amount of attention in the past decade with many reports on what can be done in flow Until recently, however, the question, “Should we do this in flow?” has merely been an afterthought This review introduces readers to the basic principles and fundamentals of flow chemistry and critically discusses recent flow chemistry accounts

The Hitchhiker's Guide to Flow Chemistry

Catalytic C-C bond-forming multi-component cascade or domino reactions: pushing the boundaries of complexity in asymmetric organocatalysis.

Chiral phosphoric acids and derivatives have attracted considerable attention as a powerful tool in asymmetric catalysis. Various enantioselective reactions have been developed by using these efficient Bronsted acid organocatalysts. Although initially the activation was restricted to reactive Bronsted basic substrates, recent reports are demonstrating the versatility of phosphoric acid catalysts in the activation of carbonyl compounds in a stereochemically controlled fashion. This tutorial review gives an overview of enantioselective Bronsted acid catalyzed transformations with the main focus on carbonyl activation. Different activation modes, key features of the catalysts and the applied substrates are presented and discussed with the goal to elucidate the origin of stereoselectivity in these Bronsted acid catalyzed transformations.

Chiral Brønsted acids in enantioselective carbonyl activations – activation modes and applications

Asymmetric catalysis is a key feature of modern synthetic organic chemistry. Traditionally, different combinations of ligands and metals are used to perform highly enantioselective reactions. Since the renaissance of organocatalysis in the early 2000s, tremendous improvement in the field of metal-free catalysis has been achieved. Recently, the combination of transition metals and organocatalysts has allowed the development of new protocols enabling transformations that could not previously be realized. This article aims to present the latest contributions in the field of combined chiral Bronsted acid and metal catalyzed reactions, highlighting the advantages of these catalytic systems as well as describing the uncertainties regarding the molecular structure of the catalytically active species and the reaction mechanisms.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/chem.201001140

Unifying Metal and Brønsted Acid Catalysis—Concepts, Mechanisms, and Classifications

Cinchona alkaloid catalysts in combination with air- and moisture-stable N-trifluoromethylthiophthalimide as electrophilic SCF3 source enabled the catalytic enantioselective trifluoromethylsulfenylation. Thus, a series of α-SCF3 esters that bear a quaternary carbon stereogenic center were obtained with excellent yield and enantioselectivity. Moreover, the products can be readily converted into valuable α-SCF3 β-hydroxyesters.

N-trifluoromethylthiophthalimide: a stable electrophilic SCF3 -reagent and its application in the catalytic asymmetric trifluoromethylsulfenylation.

Recently, chiral highly acidic Bronsted acids have emerged as powerful catalysts for enantioselective C-C and C-X bond-forming reactions. Their strong acidity renders them valuable tools for the activation of imines, carbonyl compounds, and other weakly basic substrates. As a result, new perspectives are opened and highly stereoselective transformations based on the concept of chiral contact-ion-pair catalysis can be realized. This Minireview gives an overview of the design and application of these new organocatalysts and presents recent results in this rapidly growing field.

Iuliana Atodiresei

Papers

Catalytic C-C bond-forming multi-component cascade or domino reactions: pushing the boundaries of complexity in asymmetric organocatalysis.

Chiral Brønsted acids in enantioselective carbonyl activations – activation modes and applications

Unifying Metal and Brønsted Acid Catalysis—Concepts, Mechanisms, and Classifications

N-trifluoromethylthiophthalimide: a stable electrophilic SCF3 -reagent and its application in the catalytic asymmetric trifluoromethylsulfenylation.

Modulating the acidity: highly acidic Brønsted acids in asymmetric catalysis.