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1,083 results on '"Gandon, Vincent"'

151. Alkynophilicity of Group 13 MX3Salts: A Theoretical Study

Author

Yang, Shengwen, Alix, Aurélien, Bour, Christophe, and Gandon, Vincent

Abstract

The concept of alkynophilicity is revisited with group 13 MX3metal salts (M = In, Ga, Al, B; X = Cl, OTf) using M06-2X/6-31+G(d,p) calculations. This study aims at answering why some of these salts show reactivity toward enynes that is similar to that observed with late-transition-metal complexes, notably Au(I) species, and why some of them are inactive. For this purpose, the mechanism of the skeletal reorganization of 1,6-enynes into 1-vinylcyclopentenes has been computed, including monomeric (“standard”) and dimeric (superelectrophilic) activation. Those results are confronted with deactivation pathways based on the dissociation of the M–X bond. The role of the X ligand in the stabilization of the intermediate nonclassical carbocation is revealed, and the whole features required to make a good π-Lewis acid are discussed.

Published
2021
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165. Enantioselective Total Synthesis of Cymoside through a Bioinspired Oxidative Cyclization of a Strictosidine Derivative.

Author

Dou, Yingchao, Kouklovsky, Cyrille, Gandon, Vincent, and Vincent, Guillaume

Subjects
INDOLE alkaloids, ENOL ethers, NATURAL products, INDOLE, BIOSYNTHESIS, SKELETON
Abstract

The first total synthesis of the caged monoterpene indole alkaloid cymoside is reported. This natural product displays a unique hexacyclic‐fused skeleton whose biosynthesis implies an early oxidative cyclization of strictosidine. Our approach to the furo[3,2‐b]indoline framework relied on an unprecedented biomimetic sequence which started by the diastereoselective oxidation of the indole ring into a hydroxyindolenine which triggered the addition of an enol ether and was followed by the trapping of an oxocarbenium intermediate. [ABSTRACT FROM AUTHOR]

Published
2020
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166. Synthesis of Bridged Tetrahydrobenzo[b]azepines and Derivatives through an Aza‐Piancatelli Cyclization/Michael Addition Sequence.

Author

Wang, Shengdong, Guillot, Régis, Carpentier, Jean‐François, Sarazin, Yann, Bour, Christophe, Gandon, Vincent, and Lebœuf, David

Subjects
AZEPINES, OCTANE, FASHION
Abstract

Herein, we report the preparation of bridged tetrahydrobenzo[b]azepines, which was accomplished through an aza‐Piancatelli cyclization/Michael addition sequence in a one‐pot fashion from readily available precursors. It is noteworthy that a general method to access these scaffolds was hitherto unprecedented. Additionally, the multifaceted aspects of this process have been exemplified through its application to the synthesis of 2‐azabicyclo[3.2.1]octanes and bridged tetrahydrobenzo[b]oxepines, along with post‐derivatizations. [ABSTRACT FROM AUTHOR]

Published
2020
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167. Ring Expansion and 1,2‐Migration Cascade of Benzisoxazoles with Ynamides: Experimental and Theoretical Studies.

Author

Vanjari, Rajeshwer, Dutta, Shubham, Prabagar, B., Gandon, Vincent, and Sahoo, Akhila K.

Subjects
YNAMIDES, OXAZINES, SULFONYL compounds, ANNULATION, STEREOSELECTIVE reactions, SULFONAMIDES, CATALYSIS
Abstract

Demonstrated herein is an AuI‐catalyzed annulation of sulfonyl‐protected ynamides with substituted 1,2‐benzisoxazoles for the synthesis of E‐benzo[e][1,3]oxazine derivatives. The transformation involves the addition of benzisoxazole to the gold‐activated ynamide, ring expansion of the benzisoxazole fragment to provide an α‐imino vinylic gold intermediate, and 1,2‐migration of the sulfonamide motif to the masked carbene center to deliver the respective ring‐expanded benzo[e][1,3]oxazine of predominant E configuration. A trapping experiment justifies the participation of the α‐imino masked gold carbene. DFT computations also support the hypothesized mechanism and rationalize the product stereoselectivity. [ABSTRACT FROM AUTHOR]

Published
2019
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171. Asymmetric Fe II -Catalyzed Thia-Michael addition reaction to α,β-unsaturated Oxazolidin-2-one Derivatives

Author

Lauzon, Samuel, Keipour, Hoda, Gandon, Vincent, Ollevier, Thierry, Lauzon, Samuel, Keipour, Hoda, Gandon, Vincent, and Ollevier, Thierry

Abstract

A highly enantioselective FeII-catalyzed thia-Michael addition to α,β‑unsaturated carbonyl derivatives was developed. The scope of the reaction was demonstrated with a selection of aromatic, heterocyclic and aliphatic thiols, and various Michael acceptors. The corresponding β-thioethers were obtained in good to excellent yields (up to 98%) and moderate to excellent enantioselectivities (up to 96:4 er). Unusual hepta-coordination of the metal and chelation to α,β-unsaturated oxazolidin-2-one derivatives allowed the construction of a coherent model rationalizing the enantioselective event. DFT calculations support the proposed model for observed stereoselectivities.

Published
2017

184. Assessing Ligand and Counterion Effects in the Noble Metal Catalyzed Cycloisomerization Reactions of 1,6-Allenynes: a Combined Experimental and Theoretical Approach

Author

Jaroschik, Florian, primary, Simonneau, Antoine, additional, Lemière, Gilles, additional, Cariou, Kevin, additional, Agenet, Nicolas, additional, Amouri, Hani, additional, Aubert, Corinne, additional, Goddard, Jean-Philippe, additional, Lesage, Denis, additional, Malacria, Max, additional, Gimbert, Yves, additional, Gandon, Vincent, additional, and Fensterbank, Louis, additional

Published
2016
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194. Intermolecular Rhodium(II)‐Catalyzed Allylic C(<italic>sp</italic>3)–H Amination of Cyclic Enamides.

Author

Rey‐Rodriguez, Romain, Jestin, Grégory, Gandon, Vincent, Grelier, Gwendal, Retailleau, Pascal, Darses, Benjamin, Dauban, Philippe, and Gillaizeau, Isabelle

Subjects
RHODIUM catalysts, ALLYLIC amination, AMIDES, PIPERIDINE derivatives, TEMPERATURE effect, CHEMOSELECTIVITY
Abstract

Abstract: The intermolecular rhodium(II)‐catalyzed C(sp3)–H amination of enamides gives access to new 4‐aminopiperidine derivatives that are useful building blocks in medicinal chemistry. This efficient transformation proceeds at room temperature with complete regio‐ and chemoselectivity in favor of the allylic C(sp3)–H bond, and has a broad functional group tolerance. In addition, the matched combination of the chiral complex Rh2(S‐nta)4 [nta=(S)‐N‐1,8‐naphthoylalanine] with an optically pure (S)‐sulfonimidamide allows the isolation of allylic amines with excellent stereocontrol. [ABSTRACT FROM AUTHOR]

Published
2018
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195. Catalytic Use of Low‐Valent Cationic Gallium(I) Complexes as π‐Acids.

Author

Li, Zhilong, Thiery, Guillaume, Lichtenthaler, Martin R., Guillot, Régis, Krossing, Ingo, Gandon, Vincent, and Bour, Christophe

Subjects
METAL complexes, GALLIUM chloride, ALKENES, LEWIS acids, ARYLATION
Abstract

Abstract: Transformations of alkene and alkyne substrates relevant to π‐Lewis acid catalysis have been performed using low‐valent Ga(I) species for the first time. [Ga(I)(PhF)2]+[Al(ORF)4]− and gallium dichloride (i. e. [Ga(I)]+[GaCl4]−) proved to be efficient catalysts for cycloisomerizations, Friedel‐Crafts reactions, transfer hydrogenations, and reductive hydroarylations. Their activity is compared to more common Ga(III) complexes. This study shows that even the readily available and yet overlooked gallium dichloride salt can be a more active π‐Lewis acid catalyst than gallium trichloride or other Ga(III) species. [ABSTRACT FROM AUTHOR]

Published
2018
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196. Cascade Cyclizations of Acyclic and Macrocyclic Alkynones: Studies toward the Synthesis of Phomactin A

Author

Ciesielski, Jennifer, Gandon, Vincent, and Frontier, Alison J.

Abstract

A study of the reactivity and diastereoselectivity of the Lewis acid promoted cascade cyclizations of both acyclic and macrocyclic alkynones is described. In these reactions, a β-iodoallenolate intermediate is generated via conjugate addition of iodide to an alkynone followed by an intramolecular aldol reaction with a tethered aldehyde to afford a cyclohexenyl alcohol. The Lewis acid magnesium iodide (MgI2) was found to promote irreversible ring closure, while cyclizations using BF3·OEt2as promoter occurred reversibly. For both acyclic and macrocyclic alkynones, high diastereoselectivity was observed in the intramolecular aldol reaction. The MgI2protocol for cyclization was applied to the synthesis of advanced intermediates relevant to the synthesis of phomactin natural products, during which a novel transannular cation–olefin cyclization was observed. DFT calculations were conducted to analyze the mechanism of this unusual MgI2-promoted process.

Published
2024
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197. Experimental and Theoretical Studies on the Nazarov Cyclization/Wagner–Meerwein Rearrangement Sequence

Author

Lebœuf, David, Gandon, Vincent, Ciesielski, Jennifer, and Frontier, Alison J.

Abstract

Highly functionalized cyclopentenones can be generated by a chemoselective copper(II)-mediated Nazarov/Wagner–Meerwein rearrangement sequence of divinyl ketones. A detailed investigation of this sequence is described including a study of substrate scope and limitations. After the initial 4π electrocyclization, this reaction proceeds via two different sequential [1,2]-shifts, with selectivity that depends upon either migratory ability or the steric bulkiness of the substituents at C1 and C5. This methodology allows the creation of vicinal stereogenic centers, including adjacent quaternary centers. This sequence can also be achieved by using a catalytic amount of copper(II) in combination with NaBAr4f, a weak Lewis acid. During the study of the scope of the reaction, a partial or complete E/Zisomerization of the enone moiety was observed in some cases prior to the cyclization, which resulted in a mixture of diastereomeric products. Use of a Cu(II)-bisoxazoline complex prevented the isomerization, allowing high diastereoselectivity to be obtained in all substrate types. In addition, the reaction sequence was studied by DFT computations at the UB3LYP/6-31G(d,p) level, which are consistent with the proposed sequences observed, including E/Zisomerizations and chemoselective Wagner–Meerwein shifts.

Published
2024
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