796 research outputs found
Ragionamento a Madama N. N. sopra gli antichi ornamenti e trastulli de'Bambini
No full textdi Ignazio Paternò Castell
The “System of the Salinelle of Mt. Etna” Geosite (Paternò and Belpasso – eastern Sicily)
No full textCon il nome di Salinelle vengono chiamate
delle manifestazioni naturali di emissione di
fl uidi, con formazione anche di vulcanetti di
fango, che avvengono nei dintorni dell’abitato
di Paternò. Tre sono i siti caratterizzati da
questi fenomeni naturali: le Salinelle dei Cappuccini
o dello Stadio (Paternò), le Salinelle
del Fiume (Paternò) e le Salinelle del Vallone
Salato o di San Biagio (Belpasso). Queste
manifestazioni naturali sono caratterizzate
dall’emissione di acqua salata, generalmente
a temperatura ambiente, fango, gas ed
idrocarburi liquidi. La peculiarità di questi
siti risiede nel fatto che le emissioni fl uide,
differentemente da altri siti simili, sono originate
dalla commistione tra gas magmatici/
idrotermali, che costituiscono la maggior parte
della fase gassosa emessa, e gas crostali
provenienti da serbatoi di idrocarburi. Ciò
produce morfologie uniche, a rilievo blando,
legate all’emissione di una abbondante componente
liquida priva della frazione argillosa,
dovuta anche alla condensazione di fl uidi ad
alta entalpia di origine magmatica. Altri vulcani
di fango in Italia e nel mondo hanno invece
tipicamente emissioni prevalentemente
fangoso-argillose. Per tali motivi l’emissione
di fl uidi alle Salinelle è fortemente vincolata
all’attività profonda dell’Etna, producendo
eruzioni parossistiche spesso spettacolari e
con emissione anche di acque termalizzate, il
che rende le Salinelle interessanti anche per
studi di tipo vulcanologico e geotermale. Inoltre,
l’attività di emissione di fl uidi è continua,
a differenza di quanto accade presso altri siti.
Infi ne, all’interesse dato dalla rarità del fenomeno
geologico, alla sua estensione nonché
all’interesse geomorfologico si aggiunge il
fatto che il sito è esemplifi cativo dei fenomeni
pseudovulcanici e produce morfologie
estremamente varie e peculiari. Queste caratteristiche
rendono le Salinelle quasi uniche
nel panorama mondiale dei vulcani di fango,
poiché normalmente i gas che guidano la risalita
del fango e delle acque in questo tipo di
manifestazioni naturali sono composti quasi
interamente da metano e altri idrocarburi. Ciò
ha portato al riconoscimento delle Salinelle
tra i Geositi di interesse mondiale.Published42-475A. Energia e georisorseN/A or not JCRrestricte
The “System of the Salinelle of Mt. Etna” Geosite (Paternò and Belpasso – eastern Sicily)
No full textCon il nome di Salinelle vengono chiamate
delle manifestazioni naturali di emissione di
fl uidi, con formazione anche di vulcanetti di
fango, che avvengono nei dintorni dell’abitato
di Paternò. Tre sono i siti caratterizzati da
questi fenomeni naturali: le Salinelle dei Cappuccini
o dello Stadio (Paternò), le Salinelle
del Fiume (Paternò) e le Salinelle del Vallone
Salato o di San Biagio (Belpasso). Queste
manifestazioni naturali sono caratterizzate
dall’emissione di acqua salata, generalmente
a temperatura ambiente, fango, gas ed
idrocarburi liquidi. La peculiarità di questi
siti risiede nel fatto che le emissioni fl uide,
differentemente da altri siti simili, sono originate
dalla commistione tra gas magmatici/
idrotermali, che costituiscono la maggior parte
della fase gassosa emessa, e gas crostali
provenienti da serbatoi di idrocarburi. Ciò
produce morfologie uniche, a rilievo blando,
legate all’emissione di una abbondante componente
liquida priva della frazione argillosa,
dovuta anche alla condensazione di fl uidi ad
alta entalpia di origine magmatica. Altri vulcani
di fango in Italia e nel mondo hanno invece
tipicamente emissioni prevalentemente
fangoso-argillose. Per tali motivi l’emissione
di fl uidi alle Salinelle è fortemente vincolata
all’attività profonda dell’Etna, producendo
eruzioni parossistiche spesso spettacolari e
con emissione anche di acque termalizzate, il
che rende le Salinelle interessanti anche per
studi di tipo vulcanologico e geotermale. Inoltre,
l’attività di emissione di fl uidi è continua,
a differenza di quanto accade presso altri siti.
Infi ne, all’interesse dato dalla rarità del fenomeno
geologico, alla sua estensione nonché
all’interesse geomorfologico si aggiunge il
fatto che il sito è esemplifi cativo dei fenomeni
pseudovulcanici e produce morfologie
estremamente varie e peculiari. Queste caratteristiche
rendono le Salinelle quasi uniche
nel panorama mondiale dei vulcani di fango,
poiché normalmente i gas che guidano la risalita
del fango e delle acque in questo tipo di
manifestazioni naturali sono composti quasi
interamente da metano e altri idrocarburi. Ciò
ha portato al riconoscimento delle Salinelle
tra i Geositi di interesse mondiale.Published42-475A. Energia e georisorseN/A or not JCRrestricte
A Paternò−Büchi Approach to the Synthesis of Merrilactone A
No full textA six-step approach to the tetracyclic core of merrilactone A is described that uses an intramolecular Paternò−Büchi photoaddition to install
the key oxetane ring. Irradiation of bicyclic enone 16, constructed through cyclopentenone alkylation followed by a domino oxy-/carbopalladation
reaction, produces the tetracyclic oxetane 17 in excellent yield, having the core carbon skeleton of the target compound merrilactone A
A Paternò-Büchi approach to the synthesis of merrilactone A
No full text(Chemical Equation Presented) A six-step approach to the tetracyclic core of merrilactone A is described that uses an intramolecular Paternò- Büchi photoaddition to install the key oxetane ring. Irradiation of bicyclic enone 16, constructed through cyclopentenone alkylation followed by a domino oxy-/carbopalladation reaction, produces the tetracyclic oxetane 17 in excellent yield, having the core carbon skeleton of the target compound merrilactone A. © 2005 American Chemical Society
Expanding the Scope of the Paternò-Büchi Reaction Methodology Development and Mechanistic Studies
No full textThis thesis describes the development of the Paternò-Büchi reaction between aliphatic ketones and maleic acid derivatives. Chapter 1 discusses the current literature around oxetanes, and methods for their synthesis, particularly via the Paternò-Büchi reaction. The potential and importance of oxetane rings is highlighted, alongside current scope limitations of the Paternò-Büchi reaction. Chapter 2 investigates the Paternò-Büchi reaction between acetone and maleic anhydride to yield an oxetane product that requires further transformations to allow complete purification. A series of transformation reactions was developed to easily and diversely functionalize the formed oxetane products. A side product formed through dimerization of maleic anhydride was successfully removed after the reaction was complete. Chapter 3 expands on the scope of the Paternò-Büchi reaction by using cyclic ketones in the reaction with maleic anhydride to form a series of spirocyclic oxetanes. The initial reaction conditions were based on work presented in Chapter 2 and these conditions were optimized; the dimerization of maleic anhydride was successfully supressed with p-xylene, further increasing the isolated yield of the oxetane product. Different cyclic ketones were used in the Paternò-Büchi reaction, creating a library of oxetane-containing spirocycles. Chapter 4 includes mechanistic studies performed alongside the formation of oxetanes, such as the use of molecular oxygen in order to quench potential triplet excited states in the reaction mixture. UV-vis spectra of starting materials and reagents were collected, and the different absorption range of maleimide compared to maleic anhydride allowed for distinguishing between different possible reaction pathways of the Paternò-Büchi reaction. Chapter 5 shows a series of different electron-poor alkenes tested in the Paternò-Büchi reaction, giving mixed results. Chapter 6 provides overall conclusions, highlighting the expansion of the scope of the Paternò-Büchi reaction, as well as highlighting difficulties in establishing a full mechanistic picture for photochemical reactions. Additionally, ideas for further work are discussed. Chapter 7 provides the full experimental details and characterization of the novel compounds that have been reported in this thesis (including X-ray crystal structures)
Enantioselective Paternò–Büchi Reactions: Strategic Application of a Triplet Rebound Mechanism for Asymmetric Photocatalysis
No full textThe Paternò–Büchi reaction is the [2+2] photocycloaddition of a carbonyl with an alkene to afford oxetane products. Enantioselective catalysis of this classical photoreaction, however, has proven to be a long-standing challenge. Many of the best-developed strategies for asymmetric photochemistry are not suitable to address this problem because the interaction of carbonyls with Brønsted or Lewis acidic catalysts can alter the electronic structure of their excited state and divert their reactivity towards alternate photoproducts. We show herein that an alternative triplet rebound strategy enables the stereocontrolled reaction of an excited-state carbonyl compound in its native, unbound state. These studies have resulted in the development of the first highly enantioselective catalytic Paternò–Büchi reaction, catalyzed by a novel hydrogen-bonding chiral Ir photocatalyst
Studies on The Application of The Paternò‐Büchi Reaction to The Synthesis of Novel Fluorinated Scaffolds
No full textInternational audienceIn the context of new scaffolds obtained by photochemical reactions, Paternò-Büchi reactions between heteroaromatic, trifluoromethylphenyl ketone and electron rich alkenes to give oxetanes are described. A comprehensive study has then been carried out on the reaction of aromatic ketones with fluorinated alkenes. Depending on the substitution pattern at the oxetane ring, a metathesis reaction is described as a minor side process to give mono fluorinated alkenes. Overall, this last reaction corresponds to a photo-Wittig reactions and yield amid isosteres. In order to explain the uncommon regioselectivity of the Paternò-Büchi reaction with these alkenes, electrostatic-potential derived charges (ESP) have been determined. In a second computational study, the relative stabilities of the typical 1,4-diradical intermediates of the Paternò-Büchi reaction have been determined. The results well explain the regioselectivity. Further transformations of the oxetanes or previous functionalization of the fluoroalkenes open perspectives for oxetanes as core structures for biologically active compounds
Functionalized Azetidines Via Visible Light-Enabled Aza Paternò-Büchi Reactions
No full textAzetidines are four-membered nitrogen-containing heterocycles that hold great promise in current medicinal chemistry due to their desirable pharmacokinetic effects. However, a lack of efficient synthetic methods to access functionalized azetidines has hampered their incorporation into pharmaceutical lead structures. As [2+2] cycloaddition reaction between imines and alkenes, the aza Paternò-Büchi reaction arguably represents the most direct approach to functionalized azetidines. Currently, competing reaction paths accessible upon photochemical excitation of the substrates greatly restrict the synthetic utility of these transformations. We herein report the development of a visible light-enabled aza Paternò-Büchi reaction that surmounts existing limitations and represents a general solution for the direct formation of functionalized azetidines from imine and alkene containing precursors.</p
Functionalized Azetidines Via Visible Light-Enabled Aza Paternò-Büchi Reactions
No full textAzetidines are four-membered nitrogen-containing heterocycles that hold great promise in current medicinal chemistry due to their desirable pharmacokinetic effects. However, a lack of efficient synthetic methods to access functionalized azetidines has hampered their incorporation into pharmaceutical lead structures. As [2+2] cycloaddition reaction between imines and alkenes, the aza Paternò-Büchi reaction arguably represents the most direct approach to functionalized azetidines. Currently, competing reaction paths accessible upon photochemical excitation of the substrates greatly restrict the synthetic utility of these transformations. We herein report the development of a visible light-enabled aza Paternò-Büchi reaction that surmounts existing limitations and represents a general solution for the direct formation of functionalized azetidines from imine and alkene containing precursors.</p
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