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Addition of a Reformatsky reagent to α-aryl(alkyl) α-trifluoromethyl N-tert-butanesulfinyl hemiaminals, bench-stable surrogates of trifluoromethyl ketoimines, provided β-alkyl(aryl) β-trifluoromethyl β-amino acids derivatives in good yields and high diastereoselectivities. The N-tert-butanesulfinyl β3,3-amino esters were further utilized as versatile intermediates for the elaboration of heterodi- and -tripeptides. © 2012 American Chemical Society.

Muzart J.,CNRS Institute of Molecular Chemistry - Reims
Journal of Molecular Catalysis A: Chemical | Year: 2010

This review surveys the different asymmetric and non-asymmetric Pd-catalyzed heterocyclizations of allylic alcohols, esters, ethers, carbonates, amines or silanes and vinyl epoxides, which bear a hydroxylated tether. Lactones or carbonates have been obtained from reactions carried out under carbon oxide or carbon dioxide atmosphere, respectively. The dichotomy between the mechanisms of the Pd0 and PdII processes is emphasized. © 2009 Elsevier B.V. All rights reserved.

Hoffmann N.,CNRS Institute of Molecular Chemistry - Reims
ChemSusChem | Year: 2012

Since the time of Giacomo Ciamician at the beginning of the 20th century, photochemical transformations have been recognized as contributing to sustainable chemistry. Electronic excitation significantly changes the reactivity of chemical compounds. Thus, the application of activation reagents is frequently avoided and transformations can be performed under mild conditions. Catalysis plays a central role in sustainable chemistry. Stoichiometric amounts of activation reagents are often avoided. This fact and the milder catalytic reaction conditions diminish the formation of byproducts. In the case of homogeneous catalysis, organometallic compounds are often applied. The combination of both techniques develops synergistic effects in the sense of "Green Chemistry". Herein, metal carbonyl-mediated reactions are reported. These transformations are of considerable interest for the synthesis of complex polyfunctionalized compounds. Copper(I)-catalyzed [2+2] photocycloaddition gives access to a large variety of cyclobutane derivatives. Currently, a large number of publications deal with photochemical electron-transfer-induced reactions with organometallic and coordination compounds, particularly with ruthenium complexes. Several photochemically induced oxidations can easily be performed with air or molecular oxygen when they are catalyzed with organometallic complexes. Photochemical reaction conditions also play a certain role in C-H activation with organometallic catalysts, for instance, with alkanes, although such transformations are conveniently performed with a variety of other photochemical reactions. Solar powered: Photochemical conditions significantly alter the outcome of chemical reactions. Consequently, the scope of catalytic transformations with organometallic and coordination compounds is also considerably enlarged. This article provides a short overview on such reactions and their application to organic synthesis. The review also indicates synergistic effects of photochemistry and catalysis with perspectives for a sustainable chemistry. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hoffmann N.,CNRS Institute of Molecular Chemistry - Reims
Photochemical and Photobiological Sciences | Year: 2012

Electronic excitation significantly changes the reactivity of chemical compounds. Compared to ground state reactions, photochemical reactions considerably enlarge the application spectrum of a particular functional group in organic synthesis. Multistep syntheses may be simplified and perspectives for target oriented synthesis (TOS) and diversity oriented synthesis (DOS) are developed. New compound families become available or may be obtained more easily. In contrast to common chemical reagents, photons don't generate side products resulting from the transformation of a chemical reagent. Therefore, they are considered as a traceless reagent. Consequently, photochemical reactions play a central role in the methodology of sustainable chemistry. This aspect has been recognized since the beginning of the 20th century. As with many other photochemical transformations, photochemical reactions of aromatic, benzene-like compounds illustrate well the advantages in this context. Photochemical cycloadditions of aromatic compounds have been investigated for a long time. Currently, they are applied in various fields of organic synthesis. They are also studied in supramolecular structures. The phenomena of reactivity and stereoselectivity are investigated. During recent years, photochemical electron transfer mediated reactions are particularly focused. Such transformations have likewise been performed with aromatic compounds. Reactivity and selectivity as well as application to organic synthesis are studied. © The Royal Society of Chemistry and Owner Societies 2012.

Hoffmann N.,CNRS Institute of Molecular Chemistry - Reims
Journal of Photochemistry and Photobiology C: Photochemistry Reviews | Year: 2014

Helicenes are composed of ortho annellated benzene moieties. Similar compounds contain heterocyclic or dihydrobenzene rings or smaller rings such as cyclopentadiene or cyclobutadiene (as part of benzocyclobutene units). The present article resumes photochemical reactions used for the preparation of these compounds. A very important and generally applicable reaction used for the synthesis of helicenes and helicene-like compounds is the photocyclization of stilbene subunits followed by oxidation. This reaction is often highly regioselective. The reaction can be conducted in the way that the formation of the helicene structure is favored. This selectivity is caused by the sum of the free valence numbers in the different positions of the stilbene precursor. Very fascinating structures are obtained with the cobalt catalyzed Vollhardt reaction which is photolytically supported. Helicenes are chiral and different methods of asymmetric synthesis were applied to the preparation of these compounds. A very convenient method is optical resolution using HPLC which is now currently used. © 2013 Elsevier B.V.

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