Melchiorre P.,Catalan Institution for Research and Advanced Studies |
Melchiorre P.,Institute of Chemical Research of Catalonia
Angewandte Chemie - International Edition | Year: 2012
Asymmetric aminocatalysis exploits the potential of chiral primary and secondary amines to catalyze asymmetric reactions. It has greatly simplified the functionalization of carbonyl compounds while ensuring high enantioselectivity. Recent advances in cinchona-based primary amine catalysis have provided new synthetic opportunities and conceptual perspectives for successfully attacking major challenges in carbonyl compound chemistry, which traditional approaches have not been able to address. This Review outlines the historical context for the development of this catalyst class while charting the landmark discoveries and applications that have further expanded the synthetic potential of aminocatalysis. Primary choice: In only five years, cinchona-based primary amine catalysis has almost equaled the high level of efficiency and reliability of aminocatalysis by proline-derived catalysts, offering the unique possibility of effecting reactions between sterically demanding carbonyl compounds (see picture). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Ballester P.,Institute of Chemical Research of Catalonia |
Ballester P.,Catalan Institution for Research and Advanced Studies
Accounts of Chemical Research | Year: 2013
Chemical intuition suggests that anions and π-aromatic systems would repel each other. Typically, we think of cations as being attracted to electron-rich π-systems of aromatic rings, and the cation-π interaction, a well-established noncovalent interaction, plays an important role in nature. Therefore the anion-π interaction can be considered the opposite of the cation-π interaction. Computational studies of simple models of anion-π interactions have provided estimates of the factors that govern the binding geometry and the binding energy, leading to a general consensus about the nature of these interactions. In order to attract an anion, the charge distribution of the aromatic system has to be reversed, usually through the decoration of the aromatic systems with strongly electron-withdrawing groups. Researchers have little doubt about the existence of attractive anion-π interactions in the gas phase and in the solid state. The bonding energies assigned to anion-π interactions from quantum chemical calculations and gas phase experiments are significant and compare well with the values obtained for cation-π interactions. In solution, however, there are few examples of attractive anion-π interactions.In this Account, I describe several examples of neutral molecular receptors that bind anions in solution either solely through anion-π interactions or as a combination of anion-π interactions and hydrogen bonding. In the latter cases, the strength of the anion-π interaction is indirectly detected as a modulation of the stronger hydrogen bonding interaction (enforced proximity). The dissection of the energy contribution of the anion-π interaction to the overall binding is complex, which requires the use of appropriate reference systems.This Account gives an overview the experimental efforts to determine the binding energies that can be expected from anion-π interactions in solution with examples that center around the recognition of halides. The studies show that anion-π interactions also exist in solution, and the free energy of binding estimated for these attractive interactions is less than 1 kcal/mol for each substituted phenyl groups. The quantification of anion-π interactions in solution relies on the use of molecular recognition model systems; therefore researchers need to consider how the structure of the model system can alter the magnitude of the observed energy values. In addition, the recognition of anions in solution requires the use of salts (ion pairs) as precursors, which complicates the analysis of the titration data and the corresponding estimate of the binding strength. In solution, the weak binding energies suggest that anion-π interactions are not as significant for the selective or enhanced binding of anions but offer potential applications in catalysis and transport within functional synthetic and biological systems. © 2012 American Chemical Society.
Cornella J.,Institute of Chemical Research of Catalonia |
Zarate C.,Institute of Chemical Research of Catalonia |
Martin R.,Institute of Chemical Research of Catalonia |
Martin R.,Catalan Institution for Research and Advanced Studies
Chemical Society Reviews | Year: 2014
In 1979, the seminal work of Wenkert set the standards for the utilization of aryl and vinyl ethers as coupling partners via C-O bond-cleavage. Although the topic remained dormant for almost three decades, the last few years have witnessed a renaissance in this area of expertise, experiencing an exponential growth and becoming a significant discipline within the cross-coupling arena. The means to utilize readily accessible aryl or vinyl ethers as counterparts does not only represent a practical, powerful and straightforward alternative to organic halides, but also constitutes an excellent opportunity to improve our chemical knowledge about a relatively unexplored area of expertise. This review summarizes the most significant developments in the area of C-O bond-cleavage when employing aryl or vinyl ethers, providing a detailed overview of the current state of the art and including future aspects, when applicable. This journal is © the Partner Organisations 2014.
Etayo P.,Institute of Chemical Research of Catalonia |
Vidal-Ferran A.,Institute of Chemical Research of Catalonia |
Vidal-Ferran A.,Catalan Institution for Research and Advanced Studies
Chemical Society Reviews | Year: 2013
During the last few decades, rhodium-catalysed asymmetric hydrogenation of diverse alkene classes has emerged as a powerful synthetic tool in the pharmaceutical industry, contributing to the manufacturing of chiral drugs, recent drug candidates for clinical trials, and major synthetic precursors of drugs. Numerous efficient chiral rhodium complexes, most of which are derived from enantiopure phosphorus ligands, have been employed for the preparation of chiral drugs and intermediates thereof. This review article is intended to provide an updated overview of the most striking contributions in this field, organised according to substrate class: acrylate derivatives, itaconate derivatives, α-substituted enamides, α-arylenol acetates, and minimally functionalised olefins. © The Royal Society of Chemistry 2013.
Tomashenko O.A.,Institute of Chemical Research of Catalonia |
Grushin V.V.,Institute of Chemical Research of Catalonia
Chemical Reviews | Year: 2011
Since the discovery of the McLoughlin-Thrower reaction in 1960s, considerable progress has been made in the important, demand-driven area of metal-promoted and metal-catalyzed aromatic trifluoromethylation. Important advancements have also been made in the development of Cu-catalyzed trifluoromethylations, and Ar-CF3 bond formation with well defined Cu(I) complexes. Although in some cases aryl bromides can be successfully used in Cu-mediated perfluoroalkylation reactions, iodoarenes are much more preferred due to their enhanced reactivity. Palladium is incomparably more costly than copper. Therefore, a utilizable nucleophilic aromatic trifluoromethylation process based on Pd must use catalytic, minimal quantities of this precious metal. Furthermore, many ligands employed in various Pd-catalyzed reactions often cost more than the metal itself. Another problem associated with the development of new ligands for Pd-catalyzed trifluoromethylation reactions is the facile transmetalation reaction.