73 research outputs found
Total Synthesis of Tulearin C
With the help of the smaller brother: Although alkyne metathesis will always be the little brother of alkene metathesis, it allows problems to be solved that are currently beyond reach of the more famous sibling. This notion is exemplified by the tulearin macrolides, which could only be selectively forged by ring-closing alkyne metathesis (RCAM)/transâ
reduction using the latest generation of alkyne metathesis catalysts
A New Method for the Preparation of Non-Terminal Alkynes: Application to the Total Syntheses of Tulearinâ A and C
Lactones are known to react with the reagent generated in situ from CCl4 and PPh3 in a Wittig-type fashion to give gem-dichloro-olefin derivatives. Such compounds are now shown to undergo reductive alkylation on treatment with organolithium reagents RLi to furnish acetylene derivatives bearing the substituent R at their termini (R=Me, n-, sec-, tert-alkyl, silyl); the reaction can be catalyzed with either Cu(acac)2 or Fe(acac)3/1,2-diaminobenzene. Two alkynol derivatives prepared in this way from readily accessible lactone precursors served as the key building blocks for the total syntheses of the cytotoxic marine macrolides tulearinâ
A (1) and C (2). The assembly of these fragile targets hinged upon ring closing alkyne metathesis (RCAM) followed by a formal trans-reduction of the resulting cycloalkynes via trans-hydrosilylation/protodesilylation
Reactivity of polar organometallic compounds in unconventional reaction media : challenges and opportunities
Developing new green solvents in designing chemical products and processes or successfully employing the already existing ones is one of the key subjects in green chemistry and is especially important in organometallic chemistry, which is an interdisciplinary field. Can we advantageously also use unconventional reaction media in place of current harsh organic solvents for polar organometallic compounds? This microreview critically analyses the state of the art with regard to this topic and showcases recent developments and breakthroughs that are becoming new research directions in this field. Because metals cover a vast swath of the Periodic Table the content is organised into three sections discussing the reactivity of organometallic compounds of s-, p- and d-block elements in unconventional solvents
ChemInform Abstract: Gold-Catalyzed Hydroamination/Cycloisomerization Reaction of 1,6-Enynes.
ChemInform Abstract: Synthesis of Functionalized Carbo- and Heterocycles via Gold-Catalyzed Cycloisomerization Reactions of Enynes.
MĂ©canismes de contrĂŽle de lâabsorption de CO2 anthropique et de lâacidification des eaux dans les ocĂ©ans Atlantique Nord et Indien Austral
The ocean plays a very large role in the climate system due to the large exchange of carbon dioxide with the atmosphere and the recent shift of the exchanges towards a large oceanic sink of CO2 in the Anthropocene era. The North Atlantic and the Southern oceans are acknowledged to be major repositories of this anthropogenic carbon (Cant). Indeed, ~25% of the Cant penetrates through the surface waters of the North Atlantic and ~40% reside in the intermediate and mode waters of the Southern ocean. It has been established that this oceanic carbon sink presents a large time variability of seasonal to multidecadal times scales, but that is poorly known, resulting in large uncertainties in long term climate predictions. It has thus been recommended to focus observing efforts in the regions where the absorption of CO2 is large: the North Atlantic and the Southern oceans. In this frame, the study of the seasonal to decadal variability of the oceanic carbonate system is required to better understand the effects of current changes on the oceanic carbon cycle. I use data collected since the mid-1990s until 2021 within the framework of the two French surveys SURATLANT and OISO, in order to describe the spatial and temporal variability of parameters of the carbonate system (AT, CT, fCO2, pH and ÎŽ13CDIC) in the North Atlantic subpolar gyre (NASPG) as well as in the Indian sector of the Southern Ocean. I studied the physical and biogeochemical processes that control the evolution of fCO2, water acidification and the oceanic Suess effect, separating the anthropogenic induced changes from natural variability. The long-term evolution of fCO2 and pH during the period samples has a similar magnitude to the atmospheric CO2 increase and the overall surface ocean trends. Nonetheless, results can differ from this average view, depending on season, the particular region or specific periods. Cant increase has been identified as the prime driver controlling the observed changes in fCO2 and pH, but other processes modulate these tendencies. For instance, the warming (cooling) of the surface waters will increase (restrain) the increase of fCO2 and the decrease of pH. Furthermore, an increase of AT has been identified in both regions, which partially limit the increase of ocean acidification induced by Cant increase. Also, the data suggest that changes have been smaller since 2010, with even some reversal in the increase in fCO2 and ocean acidification, both in the NASPG than in the Antarctic region of the Southern Indian ocean. 13CDIC data seem to reinforce these conclusions and to identify a different Suess effect in the two regions. This additional parameter has nonetheless been less sampled and the current data do not allow to clearly identify the change since 2010. My work supports the need to continue the long-term observations in these key regions for anthropogenic CO2 export to the deep ocean, in order to better characterize the changes in anthropogenic carbon, the oceanic Suess effect, and the acidification of surface waters for the next decades.LâocĂ©an joue un rĂŽle important dans le systĂšme climatique du fait des importants Ă©changes de gaz carbonique avec lâatmosphĂšre et du dĂ©placement de ses Ă©changes vers un puits ocĂ©anique lors de lâAnthropocĂšne. Les ocĂ©ans Atlantique Nord et Austral sont reconnus comme Ă©tant des acteurs majeurs de cette sĂ©questration du carbone anthropique (Cant). En effet, ~25% du Cant pĂ©nĂštre dans les eaux de surface de lâAtlantique Nord et ~40% rĂ©sident dans les eaux modales et intermĂ©diaires de lâocĂ©an Austral. Il est clairement Ă©tabli que le puits de carbone prĂ©sente des variations dans le temps mais mal connues, rendant les prĂ©visions climatiques difficiles. Il est donc recommandĂ© de concentrer les efforts dâobservations dans les rĂ©gions oĂč lâabsorption de CO2 est Ă©levĂ©e : les ocĂ©ans Atlantique Nord et Austral. Dans ce contexte, lâĂ©tude de la variabilitĂ© saisonniĂšre, interannuelle Ă dĂ©cennale des paramĂštres du systĂšme des carbonates dans ces deux rĂ©gions est requise pour apprĂ©hender lâimpact des changements actuels sur le cycle du carbone ocĂ©anique. BasĂ©e sur des observations acquises dĂšs le milieu des annĂ©es 1990 et jusquâen 2021 dans le cadre des programmes français SURATLANT et OISO, ces travaux de thĂšse visent Ă dĂ©crire lâĂ©volution spatiale et temporelle des paramĂštres du systĂšme des carbonates (AT, CT, fCO2, pH et ÎŽ13CDIC) dans le gyre subpolaire nord Atlantique (NASPG) et le secteur Indien de lâocĂ©an Austral. Les processus physiques et biogĂ©ochimiques contrĂŽlant lâĂ©volution de la fCO2, de lâacidification des eaux et de lâeffet Suess ocĂ©anique, ont Ă©tĂ© Ă©tudiĂ©s en sĂ©parant le signal anthropique des signaux naturels. LâĂ©volution de la fCO2 et du pH, sur lâensemble de la pĂ©riode et dans ces deux rĂ©gions, est en accord avec lâaugmentation de CO2 atmosphĂ©rique et les tendances moyennes pour lâocĂ©an global. Toutefois, selon la saison, la zone sĂ©lectionnĂ©e ou sur de plus courtes pĂ©riodes, les rĂ©sultats peuvent ĂȘtre diffĂ©rents. Lâaugmentation du Cant a Ă©tĂ© identifiĂ© comme le driver contrĂŽlant majoritairement les changements de fCO2 et pH observĂ©s, mais dâautres processus peuvent moduler ces tendances. Ainsi, le rĂ©chauffement (refroidissement) des eaux de surface accĂ©lĂšre (limite) lâaugmentation de la fCO2 et la diminution du pH. De plus, des tendances Ă lâaugmentation de AT ont Ă©galement Ă©tĂ© observĂ©es dans chacune des deux rĂ©gions, ce qui a limitĂ© en partie lâacidification des eaux par rapport Ă lâaugmentation du Cant. Cependant, les rĂ©sultats suggĂšrent une certaine stabilitĂ©, voir une inversion de la tendance Ă lâaugmentation de la fCO2 et de lâacidification autour de 2010, tant dans le NASPG que dans la zone antarctique de lâocĂ©an Indien Austral. Les observations de 13CDIC semblent confirmer cette analyse et permettent de mettre en avant un effet Suess diffĂ©rent entre les deux rĂ©gions. Ce paramĂštre complĂ©mentaire a cependant Ă©tĂ© moins Ă©chantillonnĂ© et ne permet pas encore de valider les changements observĂ©s autour de 2010. Mon travail met en avant lâimportance de maintenir des observations Ă long terme dans ces rĂ©gions oĂč lâabsorption de CO2 atmosphĂ©rique est importante, afin de suivre lâĂ©volution du carbone anthropique, de lâeffet Suess ocĂ©anique et de lâacidification des eaux de surface au cours des prochaines dĂ©cennies
Mechanisms controlling anthropogenic CO2 uptake and acidification in North Atlantic and Southern Indian Ocean waters
LâocĂ©an joue un rĂŽle important dans le systĂšme climatique du fait des importants Ă©changes de gaz carbonique avec lâatmosphĂšre et du dĂ©placement de ses Ă©changes vers un puits ocĂ©anique lors de lâAnthropocĂšne. Les ocĂ©ans Atlantique Nord et Austral sont reconnus comme Ă©tant des acteurs majeurs de cette sĂ©questration du carbone anthropique (Cant). En effet, ~25% du Cant pĂ©nĂštre dans les eaux de surface de lâAtlantique Nord et ~40% rĂ©sident dans les eaux modales et intermĂ©diaires de lâocĂ©an Austral. Il est clairement Ă©tabli que le puits de carbone prĂ©sente des variations dans le temps mais mal connues, rendant les prĂ©visions climatiques difficiles. Il est donc recommandĂ© de concentrer les efforts dâobservations dans les rĂ©gions oĂč lâabsorption de CO2 est Ă©levĂ©e : les ocĂ©ans Atlantique Nord et Austral. Dans ce contexte, lâĂ©tude de la variabilitĂ© saisonniĂšre, interannuelle Ă dĂ©cennale des paramĂštres du systĂšme des carbonates dans ces deux rĂ©gions est requise pour apprĂ©hender lâimpact des changements actuels sur le cycle du carbone ocĂ©anique. BasĂ©e sur des observations acquises dĂšs le milieu des annĂ©es 1990 et jusquâen 2021 dans le cadre des programmes français SURATLANT et OISO, ces travaux de thĂšse visent Ă dĂ©crire lâĂ©volution spatiale et temporelle des paramĂštres du systĂšme des carbonates (AT, CT, fCO2, pH et ÎŽ13CDIC) dans le gyre subpolaire nord Atlantique (NASPG) et le secteur Indien de lâocĂ©an Austral. Les processus physiques et biogĂ©ochimiques contrĂŽlant lâĂ©volution de la fCO2, de lâacidification des eaux et de lâeffet Suess ocĂ©anique, ont Ă©tĂ© Ă©tudiĂ©s en sĂ©parant le signal anthropique des signaux naturels. LâĂ©volution de la fCO2 et du pH, sur lâensemble de la pĂ©riode et dans ces deux rĂ©gions, est en accord avec lâaugmentation de CO2 atmosphĂ©rique et les tendances moyennes pour lâocĂ©an global. Toutefois, selon la saison, la zone sĂ©lectionnĂ©e ou sur de plus courtes pĂ©riodes, les rĂ©sultats peuvent ĂȘtre diffĂ©rents. Lâaugmentation du Cant a Ă©tĂ© identifiĂ© comme le driver contrĂŽlant majoritairement les changements de fCO2 et pH observĂ©s, mais dâautres processus peuvent moduler ces tendances. Ainsi, le rĂ©chauffement (refroidissement) des eaux de surface accĂ©lĂšre (limite) lâaugmentation de la fCO2 et la diminution du pH. De plus, des tendances Ă lâaugmentation de AT ont Ă©galement Ă©tĂ© observĂ©es dans chacune des deux rĂ©gions, ce qui a limitĂ© en partie lâacidification des eaux par rapport Ă lâaugmentation du Cant. Cependant, les rĂ©sultats suggĂšrent une certaine stabilitĂ©, voir une inversion de la tendance Ă lâaugmentation de la fCO2 et de lâacidification autour de 2010, tant dans le NASPG que dans la zone antarctique de lâocĂ©an Indien Austral. Les observations de 13CDIC semblent confirmer cette analyse et permettent de mettre en avant un effet Suess diffĂ©rent entre les deux rĂ©gions. Ce paramĂštre complĂ©mentaire a cependant Ă©tĂ© moins Ă©chantillonnĂ© et ne permet pas encore de valider les changements observĂ©s autour de 2010. Mon travail met en avant lâimportance de maintenir des observations Ă long terme dans ces rĂ©gions oĂč lâabsorption de CO2 atmosphĂ©rique est importante, afin de suivre lâĂ©volution du carbone anthropique, de lâeffet Suess ocĂ©anique et de lâacidification des eaux de surface au cours des prochaines dĂ©cennies.The ocean plays a very large role in the climate system due to the large exchange of carbon dioxide with the atmosphere and the recent shift of the exchanges towards a large oceanic sink of CO2 in the Anthropocene era. The North Atlantic and the Southern oceans are acknowledged to be major repositories of this anthropogenic carbon (Cant). Indeed, ~25% of the Cant penetrates through the surface waters of the North Atlantic and ~40% reside in the intermediate and mode waters of the Southern ocean. It has been established that this oceanic carbon sink presents a large time variability of seasonal to multidecadal times scales, but that is poorly known, resulting in large uncertainties in long term climate predictions. It has thus been recommended to focus observing efforts in the regions where the absorption of CO2 is large: the North Atlantic and the Southern oceans. In this frame, the study of the seasonal to decadal variability of the oceanic carbonate system is required to better understand the effects of current changes on the oceanic carbon cycle. I use data collected since the mid-1990s until 2021 within the framework of the two French surveys SURATLANT and OISO, in order to describe the spatial and temporal variability of parameters of the carbonate system (AT, CT, fCO2, pH and ÎŽ13CDIC) in the North Atlantic subpolar gyre (NASPG) as well as in the Indian sector of the Southern Ocean. I studied the physical and biogeochemical processes that control the evolution of fCO2, water acidification and the oceanic Suess effect, separating the anthropogenic induced changes from natural variability. The long-term evolution of fCO2 and pH during the period samples has a similar magnitude to the atmospheric CO2 increase and the overall surface ocean trends. Nonetheless, results can differ from this average view, depending on season, the particular region or specific periods. Cant increase has been identified as the prime driver controlling the observed changes in fCO2 and pH, but other processes modulate these tendencies. For instance, the warming (cooling) of the surface waters will increase (restrain) the increase of fCO2 and the decrease of pH. Furthermore, an increase of AT has been identified in both regions, which partially limit the increase of ocean acidification induced by Cant increase. Also, the data suggest that changes have been smaller since 2010, with even some reversal in the increase in fCO2 and ocean acidification, both in the NASPG than in the Antarctic region of the Southern Indian ocean. 13CDIC data seem to reinforce these conclusions and to identify a different Suess effect in the two regions. This additional parameter has nonetheless been less sampled and the current data do not allow to clearly identify the change since 2010. My work supports the need to continue the long-term observations in these key regions for anthropogenic CO2 export to the deep ocean, in order to better characterize the changes in anthropogenic carbon, the oceanic Suess effect, and the acidification of surface waters for the next decades
De l'Asepsie dans la pratique chirurgicale, procédés de stérilisation de Robert et Leseurre
Contient une table des matiĂšresAvec mode text
Room temperature Au(I)-catalyzed C-C bond formation through a tandem Friedel-Crafts-type addition/carbocyclization reactions
International audienc
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