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Papers by emmanuel Riguet

The Journal of Organic Chemistry

The synthesis of cyclic, chiral α-trifluoromethylated N,O-acetals having a protected cis-diol moi... more The synthesis of cyclic, chiral α-trifluoromethylated N,O-acetals having a protected cis-diol moiety has been readily achieved in two steps from a known bis-Weinreb amide derived from l-tartaric acid. The reaction of O-acetyl analogues of these N,O-acetals with triflic acid in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) at 0 °C generated in situ the corresponding electrophilic α-trifluoromethyl N-acyliminium ions that undergo Pictet-Spengler-type cyclizations. After only 10 min of reaction, the original enantiopure aza-tricyclic scaffolds bearing a trifluoromethyl substituent at the bridgehead position were obtained with diastereoselectivities ranging from 75:25 to 97:3.

Organic & Biomolecular Chemistry

Condensation reactions of unprotected tetroses and pentoses with hydroxylamines afforded nitrones... more Condensation reactions of unprotected tetroses and pentoses with hydroxylamines afforded nitrones, which were easily converted to densely functionalized isoxazolidines in the presence of electron-poor alkenes.

Chemical Communications

The asymmetric allylic alkylation of α-aryl γ-lactones involving the activation of Morita–Baylis–... more The asymmetric allylic alkylation of α-aryl γ-lactones involving the activation of Morita–Baylis–Hillman carbonates by an original chiral Lewis base is reported.

Synthesis

The synthesis of γ-lactones α-substituted with heterocycles and electron-rich aromatic rings is d... more The synthesis of γ-lactones α-substituted with heterocycles and electron-rich aromatic rings is described. The method, based on a sequence involving an organocatalytic addition of boronic acid to the 5-hydroxyfuran-2(5H)-one, followed by reduction and lactonization, gives access to broad range of γ-lactones on a gram scale. Among these, γ-lactones bearing a benzofuran, a benzothiophene, and an indole ring were alkylated in mild catalytic conditions to construct α-quaternary stereocenters. Interesting mild oxidation reaction, using molecular oxygen, was also highlighted during this study.

Chem. Commun.

The iridium-catalysed asymmetric allylic alkylation of benzofuran γ-lactones produces 1,5-hexadie... more The iridium-catalysed asymmetric allylic alkylation of benzofuran γ-lactones produces 1,5-hexadienes that were found to be excellent substrates for an unusual heteroaromatic Cope rearrangement.

Http Www Theses Fr, 2003

L'ARN joue un role fondamental dans un grand nombre de processus biologiques et est de ce fai... more L'ARN joue un role fondamental dans un grand nombre de processus biologiques et est de ce fait considere comme une cible therapeutique importante. Les aminoglycosides sont des antibiotiques utilises en clinique qui interagissent avec l'ARN ribosomal bacterien, et perturbent ainsi la synthese proteique. Ces composes sont aussi capables de se lier a d'autres ARNs tels l'ARN de retrovirus et d'interferer ainsi avec leurs fonctions biologiques. Nous avons developpe une voix de synthese conduisant a de nouveaux derives d'aminoglycosides comportant une unite ne amine comme element de reconnaissance de l'ARN. Des conjugues comportant divers groupements capables d'induire des coupures au sein de l'ARN cible ont ainsi ete prepares ainsi que des dimeres et trimeres de neamine. Les premiers resultats obtenus dans l'evaluation biologique des composes synthetises sont decrits, certains d'entre eux sont prometteurs.

Reaction Mechanisms and Methods for Aromatic Compounds, 2015

Encyclopedia of Radicals in Chemistry, Biology and Materials, 2012

Photochemically induced radical reactions as key steps in organic synthesis are mainly reported. ... more Photochemically induced radical reactions as key steps in organic synthesis are mainly reported. In this context, photochemical electron transfer plays an important role. Currently, many ruthenium-complex photocatalyzed reactions are investigated. Such transformations have been combined with organocatalysis. Free radical intermediates are also generated in photochemical reactions of carbonyl compounds such as in the Norrish and related reactions. These transformations have also been applied in multistep synthesis. Intramolecular remote functionalization has been carried out most frequently with steroid derivatives. Application to the preparation of alkaloids has also been reported. Compounds processing sulfur-containing functional groups play a central role in free radical chemistry. Corresponding reactions have also been induced under photochemical conditions. Tin compounds are frequently used as substrate or to induce radical chain reactions. The homolytic fragmentation of these compounds has also been carried out by UV irradiation. Particularly, hexaalkylditin derivatives are activated in this way. Keywords: C-glucosides; combined photocatalysis; cyclopeptides; fullerene derivatives; macro-cyclization; nitrogen-containing heterocycles; Norrish reactions; photochemical electron transfer; remote functionalization; steroids

Starting from simple substrates, the di-π-methane photoisomerizations provide access to complex p... more Starting from simple substrates, the di-π-methane photoisomerizations provide access to complex polycyclic products that are used as synthetic intermediates in organic synthesis. The reactions take place at the singlet, or more frequently, at the triplet state. Thus electronic excitation occurs either by direct light absorption or by triplet sensitization. 1,4- and 1,3-Biradicals are typical intermediates. When aromatic compounds are transformed, the aromatic character is easily suppressed in these intermediates. In some cases, photochemical electron transfer is involved. Di-π-methane rearrangements have been carried out in a stereoselective way, for instance in the solid state. In this case, chirality is induced by the chiral environment in the crystal. Two analogous reactions of heteroatom-containing substrates, the oxa-di-π-methane- and aza-di-π-methane rearrangement, have been investigated in some detail. Particularly, the oxa-di-π-methane photoisomerization was frequently appli...

ChemInform, 2012

ABSTRACT A rearrangement of 3-hydroxymethylfurans to 3-furyl aldehydes (II) is triggered by 1O2.

Tetrahedron, 2004

In the search for molecules possessing antibiotic or antiviral properties and ribonuclease like a... more In the search for molecules possessing antibiotic or antiviral properties and ribonuclease like activity, that is, able to induce the cleavage of bacterial or viral RNA targets, we report a new route for preparing selectively neamine derivatives modified at their 4 0-and/or 5hydroxyl functions. Using trityl protective groups for the amino functions and 4-methoxybenzyl groups for the hydroxyl functions, new neamine derivatives, such as histidine, phenanthroline, flavin, adenine conjugates were efficiently obtained after a single deprotection step under acid conditions. For the first time, 4 0-modified neamine derivatives were prepared. Most of the 4 0-derivatives showed affinity and selectivity for TAR RNA close to those of the corresponding 5-derivatives. The most potent compound is the 4 0-histidine derivative 31 which binds more tightly to TAR RNA compared to its 5-isomer and neamine and recognizes selectively TAR oligonucleotides having a bulge.

Organic Letters, 2007

Photolabile protecting groups have proven their usefulness on many occasions. Their versions as l... more Photolabile protecting groups have proven their usefulness on many occasions. Their versions as linkers are however less attractive, as robustness and real orthogonality become critical issues. Safety-catch systems, where a preliminary activation phase is necessary, circumvent the problem of premature cleavage. In this work, we introduce a new safety-catch photolabile protecting group, whose cleavage requires the simultaneous presence of light and a chemical promoter.

The Journal of organic chemistry, Jan 21, 2014

The synthesis of α,γ-substituted chiral γ-lactones was quickly achieved in a one pot sequential p... more The synthesis of α,γ-substituted chiral γ-lactones was quickly achieved in a one pot sequential process. The procedure involves an enantioselective organocatalysed transfer of boronic acid to 5-hydroxyfuran-2(5H)-one, followed by an intramolecular diastereoselective Passerini-type reaction. The methodology was developed and optimized with N-Boc-indole-2-boronic acid giving access to α-indole-γ-substituted lactones in high yields and good diastereoisomeric and enantiomeric ratios. By applying the process to other boronic acids, the synthesis of structurally diversified α,γ-substituted chiral lactones was also achieved in good yields albeit with lower enantioselectivities.

The Journal of Organic Chemistry

The synthesis of cyclic, chiral α-trifluoromethylated N,O-acetals having a protected cis-diol moi... more The synthesis of cyclic, chiral α-trifluoromethylated N,O-acetals having a protected cis-diol moiety has been readily achieved in two steps from a known bis-Weinreb amide derived from l-tartaric acid. The reaction of O-acetyl analogues of these N,O-acetals with triflic acid in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) at 0 °C generated in situ the corresponding electrophilic α-trifluoromethyl N-acyliminium ions that undergo Pictet-Spengler-type cyclizations. After only 10 min of reaction, the original enantiopure aza-tricyclic scaffolds bearing a trifluoromethyl substituent at the bridgehead position were obtained with diastereoselectivities ranging from 75:25 to 97:3.

Organic & Biomolecular Chemistry

Condensation reactions of unprotected tetroses and pentoses with hydroxylamines afforded nitrones... more Condensation reactions of unprotected tetroses and pentoses with hydroxylamines afforded nitrones, which were easily converted to densely functionalized isoxazolidines in the presence of electron-poor alkenes.

Chemical Communications

The asymmetric allylic alkylation of α-aryl γ-lactones involving the activation of Morita–Baylis–... more The asymmetric allylic alkylation of α-aryl γ-lactones involving the activation of Morita–Baylis–Hillman carbonates by an original chiral Lewis base is reported.

Synthesis

The synthesis of γ-lactones α-substituted with heterocycles and electron-rich aromatic rings is d... more The synthesis of γ-lactones α-substituted with heterocycles and electron-rich aromatic rings is described. The method, based on a sequence involving an organocatalytic addition of boronic acid to the 5-hydroxyfuran-2(5H)-one, followed by reduction and lactonization, gives access to broad range of γ-lactones on a gram scale. Among these, γ-lactones bearing a benzofuran, a benzothiophene, and an indole ring were alkylated in mild catalytic conditions to construct α-quaternary stereocenters. Interesting mild oxidation reaction, using molecular oxygen, was also highlighted during this study.

Chem. Commun.

The iridium-catalysed asymmetric allylic alkylation of benzofuran γ-lactones produces 1,5-hexadie... more The iridium-catalysed asymmetric allylic alkylation of benzofuran γ-lactones produces 1,5-hexadienes that were found to be excellent substrates for an unusual heteroaromatic Cope rearrangement.

Http Www Theses Fr, 2003

L'ARN joue un role fondamental dans un grand nombre de processus biologiques et est de ce fai... more L'ARN joue un role fondamental dans un grand nombre de processus biologiques et est de ce fait considere comme une cible therapeutique importante. Les aminoglycosides sont des antibiotiques utilises en clinique qui interagissent avec l'ARN ribosomal bacterien, et perturbent ainsi la synthese proteique. Ces composes sont aussi capables de se lier a d'autres ARNs tels l'ARN de retrovirus et d'interferer ainsi avec leurs fonctions biologiques. Nous avons developpe une voix de synthese conduisant a de nouveaux derives d'aminoglycosides comportant une unite ne amine comme element de reconnaissance de l'ARN. Des conjugues comportant divers groupements capables d'induire des coupures au sein de l'ARN cible ont ainsi ete prepares ainsi que des dimeres et trimeres de neamine. Les premiers resultats obtenus dans l'evaluation biologique des composes synthetises sont decrits, certains d'entre eux sont prometteurs.

Reaction Mechanisms and Methods for Aromatic Compounds, 2015

Encyclopedia of Radicals in Chemistry, Biology and Materials, 2012

Photochemically induced radical reactions as key steps in organic synthesis are mainly reported. ... more Photochemically induced radical reactions as key steps in organic synthesis are mainly reported. In this context, photochemical electron transfer plays an important role. Currently, many ruthenium-complex photocatalyzed reactions are investigated. Such transformations have been combined with organocatalysis. Free radical intermediates are also generated in photochemical reactions of carbonyl compounds such as in the Norrish and related reactions. These transformations have also been applied in multistep synthesis. Intramolecular remote functionalization has been carried out most frequently with steroid derivatives. Application to the preparation of alkaloids has also been reported. Compounds processing sulfur-containing functional groups play a central role in free radical chemistry. Corresponding reactions have also been induced under photochemical conditions. Tin compounds are frequently used as substrate or to induce radical chain reactions. The homolytic fragmentation of these compounds has also been carried out by UV irradiation. Particularly, hexaalkylditin derivatives are activated in this way. Keywords: C-glucosides; combined photocatalysis; cyclopeptides; fullerene derivatives; macro-cyclization; nitrogen-containing heterocycles; Norrish reactions; photochemical electron transfer; remote functionalization; steroids

Starting from simple substrates, the di-π-methane photoisomerizations provide access to complex p... more Starting from simple substrates, the di-π-methane photoisomerizations provide access to complex polycyclic products that are used as synthetic intermediates in organic synthesis. The reactions take place at the singlet, or more frequently, at the triplet state. Thus electronic excitation occurs either by direct light absorption or by triplet sensitization. 1,4- and 1,3-Biradicals are typical intermediates. When aromatic compounds are transformed, the aromatic character is easily suppressed in these intermediates. In some cases, photochemical electron transfer is involved. Di-π-methane rearrangements have been carried out in a stereoselective way, for instance in the solid state. In this case, chirality is induced by the chiral environment in the crystal. Two analogous reactions of heteroatom-containing substrates, the oxa-di-π-methane- and aza-di-π-methane rearrangement, have been investigated in some detail. Particularly, the oxa-di-π-methane photoisomerization was frequently appli...

ChemInform, 2012

ABSTRACT A rearrangement of 3-hydroxymethylfurans to 3-furyl aldehydes (II) is triggered by 1O2.

Tetrahedron, 2004

In the search for molecules possessing antibiotic or antiviral properties and ribonuclease like a... more In the search for molecules possessing antibiotic or antiviral properties and ribonuclease like activity, that is, able to induce the cleavage of bacterial or viral RNA targets, we report a new route for preparing selectively neamine derivatives modified at their 4 0-and/or 5hydroxyl functions. Using trityl protective groups for the amino functions and 4-methoxybenzyl groups for the hydroxyl functions, new neamine derivatives, such as histidine, phenanthroline, flavin, adenine conjugates were efficiently obtained after a single deprotection step under acid conditions. For the first time, 4 0-modified neamine derivatives were prepared. Most of the 4 0-derivatives showed affinity and selectivity for TAR RNA close to those of the corresponding 5-derivatives. The most potent compound is the 4 0-histidine derivative 31 which binds more tightly to TAR RNA compared to its 5-isomer and neamine and recognizes selectively TAR oligonucleotides having a bulge.

Organic Letters, 2007

Photolabile protecting groups have proven their usefulness on many occasions. Their versions as l... more Photolabile protecting groups have proven their usefulness on many occasions. Their versions as linkers are however less attractive, as robustness and real orthogonality become critical issues. Safety-catch systems, where a preliminary activation phase is necessary, circumvent the problem of premature cleavage. In this work, we introduce a new safety-catch photolabile protecting group, whose cleavage requires the simultaneous presence of light and a chemical promoter.

The Journal of organic chemistry, Jan 21, 2014

The synthesis of α,γ-substituted chiral γ-lactones was quickly achieved in a one pot sequential p... more The synthesis of α,γ-substituted chiral γ-lactones was quickly achieved in a one pot sequential process. The procedure involves an enantioselective organocatalysed transfer of boronic acid to 5-hydroxyfuran-2(5H)-one, followed by an intramolecular diastereoselective Passerini-type reaction. The methodology was developed and optimized with N-Boc-indole-2-boronic acid giving access to α-indole-γ-substituted lactones in high yields and good diastereoisomeric and enantiomeric ratios. By applying the process to other boronic acids, the synthesis of structurally diversified α,γ-substituted chiral lactones was also achieved in good yields albeit with lower enantioselectivities.