Chimie organique | EPFL Graph Search

La chimie organique est le domaine de la chimie qui étudie les composés organiques, c'est-à-dire les composés du carbone (à l'exception de quelques composés simples qui par tradition relèvent de la chimie minérale). Ces composés peuvent être naturels ou synthétiques. Une caractéristique du carbone consiste en l’aptitude qu’ont ses atomes à s’enchaîner les uns aux autres, par des liaisons covalentes, d'une façon presque indéfinie, pour former des chaînes carbonées d’une grande diversité. Les composés organiques sont ainsi constitués de molécules caractérisées par des enchaînements carbonés propres aux molécules dites « organiques ». L'aptitude caractéristique du carbone implique qu'. Les molécules organiques contiennent fréquemment des atomes d’hydrogène et souvent des atomes d'oxygène ou d'azote et les molécules synthétiques proviennent souvent du pétrole. La chimie organique étudie en particulier leur structure chimique, leurs propriétés, leurs caractér

Engaging 1-Alkynyl Triazenes in Transition Metal-Catalyzed and Fluorinative Transformations

Jin Fay Tan

Triazenes have garnered great attention for their anti-cancer properties and versatility in organic chemistry. Recently, a novel synthesis of 1-alkynyl triazenes was reported. This thesis describes the compatibility, reactivity and applications of 1-alkynyl triazenes in various transition metal-catalyzed and fluorinative transformations.Chapter 1 provides an introduction to the discovery, biological activities and chemical reactivity of aryl triazenes. The recent procedure on 1-alkynyl triazene synthesis is described, followed by the context for experimental work presented in this thesis.In Chapter 2, we demonstrate Ru-catalyzed [2 + 2 + 2] cyclotrimerizations of 1-alkynyl triazenes to form densely substituted arenes and pyridines. The regioselectively installed triazenyl moiety can be elaborated into a range of useful substituents. The largely unknown coordination chemistry of 1-alkynyl triazenes with Cp*RuCl is investigated, leading to the isolation of several complexes that may provide insights into catalyst design.In Chapter 3, we explore the use of 1-alkynyl triazenes as fluoro alkyne surrogates in Rh-catalyzed olefinic C-H annulations with a rare Lossen rearrangement, leading to 4-fluoro-2-pyridones after a subsequent Wallach fluorination. The triazenyl pyridone intermediates are further transformed into other value-added fluorine-containing functional groups.In Chapter 4, we study the reactivity of 1-alkynyl triazenes in Ag-catalyzed cyclizations with propiolic acids, forming most notably the unreported 6-fluoro pyrones. A mechanistically intriguing 1,5-carbonyl transposition has been unraveled. The triazenyl unit is shown to serve as a traceless activating group for Diels-Alder cycloadditions.Chapter 5 describes perfluorinations and regiodivergent oxyfluorinations of 1-alkynyl triazenes, which provide tunable selective access to 1,1,2,2-tetrafluoro alkyl triazenes, Î±-difluoro triazenyl ketones and Î±-difluoro acyl triazenes. Mechanistic investigations of these fluorinative transformations have been subsequently explored.Finally in Chapter 6, we offer an outlook on the potential opportunities with the chemistry of 1-alkynyl triazenes.

EPFL2021

Synthetic chemistry with nitrous oxide and triazenes

Iris Roswitha Landman

Nitrous oxide (N2O) has gained much interest because of its physiological effects ("laughing gas") and its negative environmental impact ("greenhouse gas", "ozone-depleting substance"): It has a lifetime of more than 100 years in the atmosphere. Its persistent character shows how challenging it is to convert N2O into more valuable products. From a synthetic point of view, N2O has potential as diazo (N2) transfer reagent, but applications in synthetic organic chemistry are scarce. The main challenges are to capture N2O, avoid the loss of N2, and to overcome poor-selectivity and -yields. Herein, we describe two examples of the incorporation of two nitrogen atoms into the final product. Firstly, we use N2O as diazo transfer reagent in the preparation of triazolopyridines, which are valuable starting materials for heterocyclic compounds. The reactions can be performed under mild conditions and give synthetically interesting triazoles in moderate to good yields. Secondly, general methods to N1 acylated triazenes were missing previously. We developed routes to 1-acyl triazenes via acid-catalyzed hydration, or by gold- or iodine-catalyzed oxidation of 1-alkynyl triazenes. The latter compounds are prepared from N2O. The properties of the N1 acylated triazenes are distinct compared to other triazenes, displaying different physical and chemical properties. Under strong acidic conditions, 1-acyl triazenes act as acylation reagents. Finally, despite that triazene chemistry is known for more than 160 years, the preferred coordination site of acids still remained a matter of debate (N1, N2, or N3). In search of experimental evidence, we have analyzed triflic acid, B(C6F5)3, and PdCl2 adducts of triazenes by IR, NMR spectroscopy and single crystal X-ray crystallography. For all cases, we found the acid coordinating to the N1 atom of the triazene. This preference should be taken into account for future acid- and transition metal-catalyzed reactions with triazenes. Altogether, this thesis contributes to triazene chemistry and synthetic chemistry with N2O. In this way, we provide further evidence that N2O can be used as a diazo donor to get to synthetically interesting N-containing products.

EPFL2022

Ligand synthesis for homogeneous catalysis

Michael Maurin

Organophosphorus compounds found applications in varied fields of the organic chemistry: they are particularly present in natural compounds such as the deoxyribonucleic acid (DNA) and in the field of catalysis in which their utility is also proven. Thus, this thesis work first focused on the preparation of various phosphorus ligands utilizable in transition metal catalysed reactions. Being given the importance of this type of reaction in organic synthesis, it appears essential to have many ligands at disposal in order to fine-tune and to optimize the reaction conditions as much as possible. Thus, the first objective of this work was to propose a simple and general method for the preparation of monodentate phosphorus ligands. Based on the use of phosphites in substitution for the usual phosphorus trihalides, this method was initially tested during the preparation of different simple triarylphosphines. Thereafter, this method was extended to the synthesis of new ligands having more complex structures. The yields obtained for the latter as well as the variety of the substrates authorized by this method confirmed its value and suggested its application to the synthesis of new heteroaromatic phosphines. The preparation of bidentate phosphorus ligands based on chiral biphenyl motifs was then addressed. For that purpose, the 2,2',6,6' -tetrabromobiphenyl was chosen as a pivot substrate for the development of a modular synthetic approach. Indeed, by means of successive halogen/metal permutational exchanges and after treatment with the suitable electrophile, it was possible to functionalize this substrate, isolate each atropisomer in enantiomerically pure form, and finally convert each one of those into chiral biphenylbisphosphines. In addition, it was also possible, during the synthesis of these ligands, to evaluate the rotational stability of some enantiomerically pure dilithiobiphenyls by means of dynamic nuclear magnetic resonance experiments.

EPFL2007