Pierre Vogel - Academia.edu (original) (raw)
Papers by Pierre Vogel
Journal of Molecular Graphics, 1987
Abstract In order to visualize the stereochemical aspects of the Diels-Alder model cycloaddition ... more Abstract In order to visualize the stereochemical aspects of the Diels-Alder model cycloaddition of ethylene on butadiene, we developed a computer graphics animated model. The structural data base was deduced from MINDO/3 calculations, and the application program makes it possible to display in detail the different steps of the reaction mechanism. The scope of the application has been enlarged by a similar representation of the Diels-Alder cycloaddition of bis (methylene)—2,3 bicyclo [2.2.1]heptane to ethylene. Both of these examples suggest that molecular graphics is an ideal tool for visualizing and understanding the stereochemistry of complex chemical reactions.
Iminosugars
Page 1. 5 Imino-C-disaccharides and analogues: synthesis and biological activity Pierre Vogel, Sa... more Page 1. 5 Imino-C-disaccharides and analogues: synthesis and biological activity Pierre Vogel, Sandrine Gerber-Lemaire and Lucienne Juillerat-Jeanneret 5.1 Introduction The biological importance of oligosaccharides was ...
![Research paper thumbnail of Charge-transfer bands of bicyclic β,γ-unsaturated ketones. Circular dichroism of (+)-(1R)-5,6-dimethylidene-2-bicyclo[2.2.2]octanone and (+)-(1R)-2-bicyclo[2.2.2]oct-5-enone](https://attachments.academia-assets.com/115325134/thumbnails/1.jpg)
](Tetrahedron Letters, 1981
Synthesis, 1991
Protected forms of exo-5-amino-exo-6-hydroxy-7-oxabicyclo [2.2.1]heptan-2-one and of exo-5-amino-... more Protected forms of exo-5-amino-exo-6-hydroxy-7-oxabicyclo [2.2.1]heptan-2-one and of exo-5-amino-endo-6-hydroxy-7-oxabicyclo[2.2.1]heptan-2-one can be obtained readily and with high stereoselectivity from exo-2-cyano-7-oxabicyclo[2.2.1]hept-5-en-2-yl acetate (+/-)-(7). The processes involve acid promoted rearrangements of N-carbonyl aziridines 10 [(1RS,2SR,4RS,5RS, 6SR)-6-cyano-8-oxa-3-azatricyclo[3.2.10(2,4)]oct-6-yl acetate derivatives] derived from (+/-)-7.
Journal of Organometallic Chemistry, 1981
... Protonation of IIa by HCl/AlCl 3 /CH 2 Cl 2 to give the η 4 -diene : η 2 -ene : η 3 -dienyl c... more ... Protonation of IIa by HCl/AlCl 3 /CH 2 Cl 2 to give the η 4 -diene : η 2 -ene : η 3 -dienyl cationic complex Va, followed by quenching of Va with NaHCO 3 /CH 3 OH, resulted in a 1,4-addition of methanol to one coordinated s-cis ... H. Blessing, P. Coppens and P. Becker J. Appl. ...
The Journal of Organic Chemistry, 1987
The syntheses of methyl-and phenyl-substituted 2H-pyrroles 8 bearing a but-3-enyl or pent-4-enyl ... more The syntheses of methyl-and phenyl-substituted 2H-pyrroles 8 bearing a but-3-enyl or pent-4-enyl side chain are reported. The thermolyses of 8 yielded tricyclic derivatives with the 2-azabicyclo[2.2.l]hept-2-ene moiety resulting from the intramolecular Diels-Alder additions of 3H-pyrrole intermediates. No product resulting from the intramolecular cycloaddition of 2H-pyrroles or of 1H-pyrroles was observed. Thermochemical analysis and ab initio STO-3G calculations on model compounds suggested that the 2-azabicyclo[2.2.l]hept-2-enes derivatives are the only possible products under the conditions of our thermolyses. The rates of the isomerizations of 8 into the corresponding 3H-pyrroles intermediates, as well as those of their cyclizations could be enhanced in the presence of the cation-radical (4-BrCeH,),NSbCl6 or of a Lewis acid.
Inorganica Chimica Acta, 1979
... The reaction of 5, 6, 7, 8-tetrakis(methylene)bicyclo[2.2.2.]oct-2-ene (1) with Fe 2 9CO) 9 y... more ... The reaction of 5, 6, 7, 8-tetrakis(methylene)bicyclo[2.2.2.]oct-2-ene (1) with Fe 2 9CO) 9 yields under various conditions the exo and endo-tetrahaptotri-carbonyliron complexes(2 and3) and the endo, exobis(tetrahaptotricarbonyliron ... 4a. H. Blessing, P. Coppens and P. Becker. ...
![Research paper thumbnail of Iron and ruthenium carbonyls of 2,3,5,6-tetrakis(methylene)bicyclo[2.2.2]octane. Crystal and molecular structure of (C12H14)Fe(CO)3](https://attachments.academia-assets.com/115325135/thumbnails/1.jpg)
](Inorganica Chimica Acta, 1979
The reaction of 2,3,5,6tetrakis(methylene)bicycle [2.2.2]octane (la) with Fez(CO), yields the two... more The reaction of 2,3,5,6tetrakis(methylene)bicycle [2.2.2]octane (la) with Fez(CO), yields the two (q4-1,3diene)Fe(CO)3 isomers (2: exe; 3:endo) together with two bimetallic isomers (CIZH14)[Fe-(CO)3]2 (4:endo+xo; S:diexo). The reaction of la with RuB(CO)iZ yields the endo-(C1&14)Ru(CO)3 (6) and endo, exo-(C,,H,,)[Ru(CO),]z (7) complexes as the main products. The molecular structure of 3 has been determined by X-ray crystallography. The Fe(CO)J group is in the endo position with respect to the roof-shaped tetraene. The &and is bound through one diene group to two basal positions of a tetragonal pyramidal Fe(CO)9L, moiety. Hydrogen atom positions have been determined (final residual R = 0.029). The dimensions for the 1,3-butadieneirontricarbonyl system, as found in this and 41 other structures, are summarized and discussed statistically. In this study the weighted averages for all structures show the three CC distances to be of equal length and the Fe-C (inner) distance to be shorter than the Fe-C (outer) distance. The deviations of H(Z) and H(E) atoms from the butadiene plane, as found in this and 6 other structures having an exocyclic unsubstituted 1,3diene group, are also discussed. Neither thermal epimerization of iron nor epimerization catalyzed by H+ were found for complexes 2-7 whose structures in solution were deduced from their 'H and 13C NMR data on the basis of the known structure of 3. been prepared for the first time in our laboratory [l-3]. z &I Z = CHs-CHs la Z=CH=CH lb ;:; Z=CHa lc PI z=o Id [31 lad These roof-shaped molecules have two homoconjugated s&s-butadiene groups and can be attacked by metal carbonyls on their exo or endo faces, thus leading to mixtures of exo and endo-M(C0)3-diene complexes [4]. We report in this study the results of the reaction of la with iron and ruthenium carbonyls as well as the crystal structure of the endo-(C&#e(CO) 3 complex (3) and a statistical comparison of the dimensions of the 1,3_butadieneirontricarbonyl system in 42 structures. Reaction of la with Fe and Ru Carbonyls Upon treatment with yields the expected exo-8 2,3,5,6-tetrakis(methylene)bicycloalcanes lad are highly reactive polyenes which have
Helvetica Chimica Acta, 2002
ABSTRACT
![Research paper thumbnail of Radical Cation States of 2,3,5,6,7,8‐Hexamethylidenebicyclo [2.2.2]octane](https://attachments.academia-assets.com/115325132/thumbnails/1.jpg)
](Helvetica Chimica Acta, 1980
The photoelectron spectrum of the title compound is reported and assigned by correlation with the... more The photoelectron spectrum of the title compound is reported and assigned by correlation with the photoelectron spectra of related molecules.
Angewandte Chemie, 1967
nonen fur die Darstellung substituierter Benzolverbindungen [81. Versuche mit Cyclooctatetraen, 1... more nonen fur die Darstellung substituierter Benzolverbindungen [81. Versuche mit Cyclooctatetraen, 1,2-Dimethylcyclopropen-1-carbonslure-methylester und l-Cyclobuten-1,2-dicarbonsaure-dimethylester als dienophilen Partnern fur (Sa) haben auch unter drastischeren Bedingungen bisher keine ubersichtlichen Resultate ergeben. Eingegangen am 18. August 1967 [Z 601bl 230 (br.S) 265 (S)
Journal of The American Chemical Society, 2009
The potential energy surfaces of the desulfinylation of prop-2-enesulfinic acid (13) in CH 2 Cl 2... more The potential energy surfaces of the desulfinylation of prop-2-enesulfinic acid (13) in CH 2 Cl 2 solution at -15°C have been explored by quantum calculations and analyzed with kinetic data obtained for the reaction in absence or presence of additives. Monomeric 13 adopts a preferred conformation with gauche SdO/σ(C(1)-C(2) bond pairs and the O-H bond pointing toward C(3). It equilibrates with the more stable dimer (13) 2 (at -15°C) formed by two O-H · · · OdS hydrogen bonds and in which the SdO/ σC(1)-C(2) are gauche also, but the SOH moieties are antiperiplanar with respect to σ(C(1)-C(2)). Dimer (13) 2 undergoes desulfinylation into propene + SO 2 + 13 following a one-step, concerted mechanism. The preferred transition state is a six-membered, chairlike transition structure (C · · · S elongation and S-O · · · H · · · C(3) hydrogen transfer occur in concert) in which the SdO/σ(C(1)-C(2)) bonds are gauche (SdO adopt pseudoaxial positions). There are at least 48 transition states, each one defining a different pathway, all with similar calculated free energies (∆G ‡ ) 25.3-28.6 kcal/mol), which makes the bimolecular (autocatalyzed) retro-ene elimination of SO 2 competing (entropy factor) with a monomolecular process for which the transition state (calculated ∆G ‡ ) 24.3 kcal/mol) implies only one molecule of sulfinic acid. This agrees with the experimental rate law of the reaction which is first order in the concentration of dimer (13) 2 . SO 2 , CF 3 COOH, and BF 3 · Me 2 O do not catalyze the reaction. In the presence of an excess of BF 3 · Me 2 O the desulfinylation is completely inhibited due to the formation of a stable tetramolecular complex of type (CH 2 dCHCH 2 SO 2 H · BF 3 ) 2 (18), for which quantum calculations show that the SdO/σ(C(1)-C(2)) bonds are antiperiplanar whereas the S-OH/σ(C(1)-C(2)) bonds are gauche. Independently of the additive, the retro-ene eliminations of SO 2 are calculated to be concerted and have transition states adopting six-membered cyclic structures in which SdO and σ(C(1)-C(2)) are gauche, the SdO interacting with the additive. Preliminary experiments suggested that the thermodynamically unfavored ene reaction of SO 2 with propene can occur at low temperature using 1 equiv of BF 3 .
Tetrahedron: Asymmetry, 1997
The enantiomerically pure (1S,4R,4'S,5'S)-l-(4',5'-dimethyl-dioxolan-2'yl)-5,6-dimethylidene-7-ox... more The enantiomerically pure (1S,4R,4'S,5'S)-l-(4',5'-dimethyl-dioxolan-2'yl)-5,6-dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene derived from the acetal of furfural and (2S,3S)-butane-2,3-diol underwent addition to 1-acetylvinyl para-nitrobenzoate in the presence of an excess of t-BuMe2SiOSO2CF3 to yield an 83:17 mixture of two diastereomeric products which was converted into (2R)-l,2,3,4-tetrahydro-2-hydroxy-5,8dimethoxynaphthalen-2-yl methyl ketone.
Journal of Organometallic Chemistry, 1979
ABSTRACT
The Journal of Organic Chemistry, 2006
A new straightforward and inexpensive one-pot procedure is described for the preparation of enant... more A new straightforward and inexpensive one-pot procedure is described for the preparation of enantiopure five-membered cyclic nitrones starting from the corresponding lactols. Its efficiency relies on the condensation of unprotected hydroxylamine with readily available lactols and on the chemoselectivity of the subsequent esterification with methanesulfonyl chloride. The targeted enantiomerically pure pyrroline N-oxides are versatile synthetic intermediates: one of the nitrones so-obtained has been converted into new polyhydroxypyrrolizidines, analogues of the alkaloids rosmarinecine and crotanecine, which were assayed for their inhibitory activities toward 22 commercially available glycosidase enzymes. One of them ((-)-7a-epi-crotanecine) is a potent and selective inhibitor of R-mannosidases from jack beans and almonds.
Current Organic Chemistry, 2001
Zaragozic acids (or squalestatins) are very potent inhibitors of squalene synthase. They or simpl... more Zaragozic acids (or squalestatins) are very potent inhibitors of squalene synthase. They or simpler analogs have potential as drugs for lowering the endogenous level of cholesterol in human serum. These compounds are Ras farnesyltransferase inhibitors and might become antitumor drugs. They are also antifungal agents. This account presents synthetic studies subsequent to those reviewed by Nadin and Nicolaou [1]. A wealth of new chemistry has been developed for the generation of highly oxygenated 2,8-dioxabicyclo[3.2.1]octane-3,4,5-tricarboxylic triacids and analogs, so demonstrating the fascination of synthetic chemists for zaragozic acids.
Bioorganic & Medicinal Chemistry Letters, 1999
Radical C-glycosidation of a 3-methylidene-7-oxabicyclo[2.2.1]heptan-2-one derivative with acetob... more Radical C-glycosidation of a 3-methylidene-7-oxabicyclo[2.2.1]heptan-2-one derivative with acetobromomannose gave a ct-C-mannopyranoside that was converted into et-D-ManpCH2(1-~3)-D-GalNAc, a C-disaccharide that inhibits 13-galactosidase from jack bean with IC50 = 9.4 ~tM and K i = 7.5 ~M (mixed mode of inhibition).
Chemical Communications, 1999
A convergent synthesis of (1?2)-and (1?4)-Clinked imino disaccharides was achieved by applying No... more A convergent synthesis of (1?2)-and (1?4)-Clinked imino disaccharides was achieved by applying Nozaki-Kishi coupling of a hydroxyproline-derived carbaldehyde with isolevoglucosenone or levoglucosenone derived enol triflates. Carbohydrate mimetics are potentially useful tools to study cellular interactions, 1 the biosynthesis of glycoproteins, the metabolism of glycoconjugates, 2 and the mechanisms of digestion. 3 Inhibitors of the enzymes involved in these processes such as the glycosidases and the glycosyltransferases are potential anti-cancer, antiviral, and antidiabetic agents, as well as insect antifeedant agents. 4 Disaccharide mimetics such as Cdisaccharides and dideoxyiminoalditol Clinked to monosaccharides have emerged as a new class of specific glycosidase inhibitors and may represent non-hydrolyzable epitopes. 5-7 Recently we disclosed an efficient and versatile approach to the syntheses of (1?3)-C-disaccharides and (1?3)-Clinked imino disaccharides 5 based on the cross-aldolisation of the aldehydes 3 with the nucleophile 1,4-adducts 2 of isolevoglucosenone 1 (Scheme 1). 8,9 We report here that (1?4)-and (1?2)-Cdisaccharides can be prepared starting from 1 and levoglucosenone 17 with 3, respectively. Adduct 6 of benzyl alcohol with isolevoglucosenone was enolized, without elimination of benzylate anion, on treatment with LiHMDS in 95+5 THF-HMPA at 278 °C (Scheme 2). 9 Quenching of the corresponding lithium enolate with 2-[bis(trifluoromethylsulfonyl)amino]-5-chloropyridine provided the enol triflate 7 in 87% yield. 10 Nozaki-Kishi coupling of 7 and aldehyde 8 led to allylic alcohols 9 and 10 isolated in 62 and 17% yield, respectively. 11,12 ‡ Interestingly, the reaction was accelerated by ultrasound and O 2. Under N 2 atmosphere, ultrasound shortened the reaction time from 30 to 2 h. While in the presence of a catalytic amount of O 2 (5 mol% with respect to CrCl 2 , concentration of O 2 lower than 10%), the reaction time was reduced further to less than 1 h. Moreover, O 2 suppressed the formation of 11, resulting from H 2 O quenching of the alkenylchromium species, from 36 to less than 10%.
Bioorganic & Medicinal Chemistry Letters, 2001
Readily derived from d-glucose, 5-[(2R,3S,4R)-3,4-dihydroxypyrrolidin-2-yl]-2-methyl-3-furoic est... more Readily derived from d-glucose, 5-[(2R,3S,4R)-3,4-dihydroxypyrrolidin-2-yl]-2-methyl-3-furoic esters and amides are selective and competitive inhibitors (Ki≥3μM) of α-l-fucosidase from bovine epididymis and from human placenta.
Journal of Molecular Graphics, 1987
Abstract In order to visualize the stereochemical aspects of the Diels-Alder model cycloaddition ... more Abstract In order to visualize the stereochemical aspects of the Diels-Alder model cycloaddition of ethylene on butadiene, we developed a computer graphics animated model. The structural data base was deduced from MINDO/3 calculations, and the application program makes it possible to display in detail the different steps of the reaction mechanism. The scope of the application has been enlarged by a similar representation of the Diels-Alder cycloaddition of bis (methylene)—2,3 bicyclo [2.2.1]heptane to ethylene. Both of these examples suggest that molecular graphics is an ideal tool for visualizing and understanding the stereochemistry of complex chemical reactions.
Iminosugars
Page 1. 5 Imino-C-disaccharides and analogues: synthesis and biological activity Pierre Vogel, Sa... more Page 1. 5 Imino-C-disaccharides and analogues: synthesis and biological activity Pierre Vogel, Sandrine Gerber-Lemaire and Lucienne Juillerat-Jeanneret 5.1 Introduction The biological importance of oligosaccharides was ...
Tetrahedron Letters, 1981
Synthesis, 1991
Protected forms of exo-5-amino-exo-6-hydroxy-7-oxabicyclo [2.2.1]heptan-2-one and of exo-5-amino-... more Protected forms of exo-5-amino-exo-6-hydroxy-7-oxabicyclo [2.2.1]heptan-2-one and of exo-5-amino-endo-6-hydroxy-7-oxabicyclo[2.2.1]heptan-2-one can be obtained readily and with high stereoselectivity from exo-2-cyano-7-oxabicyclo[2.2.1]hept-5-en-2-yl acetate (+/-)-(7). The processes involve acid promoted rearrangements of N-carbonyl aziridines 10 [(1RS,2SR,4RS,5RS, 6SR)-6-cyano-8-oxa-3-azatricyclo[3.2.10(2,4)]oct-6-yl acetate derivatives] derived from (+/-)-7.
Journal of Organometallic Chemistry, 1981
... Protonation of IIa by HCl/AlCl 3 /CH 2 Cl 2 to give the η 4 -diene : η 2 -ene : η 3 -dienyl c... more ... Protonation of IIa by HCl/AlCl 3 /CH 2 Cl 2 to give the η 4 -diene : η 2 -ene : η 3 -dienyl cationic complex Va, followed by quenching of Va with NaHCO 3 /CH 3 OH, resulted in a 1,4-addition of methanol to one coordinated s-cis ... H. Blessing, P. Coppens and P. Becker J. Appl. ...
The Journal of Organic Chemistry, 1987
The syntheses of methyl-and phenyl-substituted 2H-pyrroles 8 bearing a but-3-enyl or pent-4-enyl ... more The syntheses of methyl-and phenyl-substituted 2H-pyrroles 8 bearing a but-3-enyl or pent-4-enyl side chain are reported. The thermolyses of 8 yielded tricyclic derivatives with the 2-azabicyclo[2.2.l]hept-2-ene moiety resulting from the intramolecular Diels-Alder additions of 3H-pyrrole intermediates. No product resulting from the intramolecular cycloaddition of 2H-pyrroles or of 1H-pyrroles was observed. Thermochemical analysis and ab initio STO-3G calculations on model compounds suggested that the 2-azabicyclo[2.2.l]hept-2-enes derivatives are the only possible products under the conditions of our thermolyses. The rates of the isomerizations of 8 into the corresponding 3H-pyrroles intermediates, as well as those of their cyclizations could be enhanced in the presence of the cation-radical (4-BrCeH,),NSbCl6 or of a Lewis acid.
Inorganica Chimica Acta, 1979
... The reaction of 5, 6, 7, 8-tetrakis(methylene)bicyclo[2.2.2.]oct-2-ene (1) with Fe 2 9CO) 9 y... more ... The reaction of 5, 6, 7, 8-tetrakis(methylene)bicyclo[2.2.2.]oct-2-ene (1) with Fe 2 9CO) 9 yields under various conditions the exo and endo-tetrahaptotri-carbonyliron complexes(2 and3) and the endo, exobis(tetrahaptotricarbonyliron ... 4a. H. Blessing, P. Coppens and P. Becker. ...
Inorganica Chimica Acta, 1979
The reaction of 2,3,5,6tetrakis(methylene)bicycle [2.2.2]octane (la) with Fez(CO), yields the two... more The reaction of 2,3,5,6tetrakis(methylene)bicycle [2.2.2]octane (la) with Fez(CO), yields the two (q4-1,3diene)Fe(CO)3 isomers (2: exe; 3:endo) together with two bimetallic isomers (CIZH14)[Fe-(CO)3]2 (4:endo+xo; S:diexo). The reaction of la with RuB(CO)iZ yields the endo-(C1&14)Ru(CO)3 (6) and endo, exo-(C,,H,,)[Ru(CO),]z (7) complexes as the main products. The molecular structure of 3 has been determined by X-ray crystallography. The Fe(CO)J group is in the endo position with respect to the roof-shaped tetraene. The &and is bound through one diene group to two basal positions of a tetragonal pyramidal Fe(CO)9L, moiety. Hydrogen atom positions have been determined (final residual R = 0.029). The dimensions for the 1,3-butadieneirontricarbonyl system, as found in this and 41 other structures, are summarized and discussed statistically. In this study the weighted averages for all structures show the three CC distances to be of equal length and the Fe-C (inner) distance to be shorter than the Fe-C (outer) distance. The deviations of H(Z) and H(E) atoms from the butadiene plane, as found in this and 6 other structures having an exocyclic unsubstituted 1,3diene group, are also discussed. Neither thermal epimerization of iron nor epimerization catalyzed by H+ were found for complexes 2-7 whose structures in solution were deduced from their 'H and 13C NMR data on the basis of the known structure of 3. been prepared for the first time in our laboratory [l-3]. z &I Z = CHs-CHs la Z=CH=CH lb ;:; Z=CHa lc PI z=o Id [31 lad These roof-shaped molecules have two homoconjugated s&s-butadiene groups and can be attacked by metal carbonyls on their exo or endo faces, thus leading to mixtures of exo and endo-M(C0)3-diene complexes [4]. We report in this study the results of the reaction of la with iron and ruthenium carbonyls as well as the crystal structure of the endo-(C&#e(CO) 3 complex (3) and a statistical comparison of the dimensions of the 1,3_butadieneirontricarbonyl system in 42 structures. Reaction of la with Fe and Ru Carbonyls Upon treatment with yields the expected exo-8 2,3,5,6-tetrakis(methylene)bicycloalcanes lad are highly reactive polyenes which have
Helvetica Chimica Acta, 2002
ABSTRACT
Helvetica Chimica Acta, 1980
The photoelectron spectrum of the title compound is reported and assigned by correlation with the... more The photoelectron spectrum of the title compound is reported and assigned by correlation with the photoelectron spectra of related molecules.
Angewandte Chemie, 1967
nonen fur die Darstellung substituierter Benzolverbindungen [81. Versuche mit Cyclooctatetraen, 1... more nonen fur die Darstellung substituierter Benzolverbindungen [81. Versuche mit Cyclooctatetraen, 1,2-Dimethylcyclopropen-1-carbonslure-methylester und l-Cyclobuten-1,2-dicarbonsaure-dimethylester als dienophilen Partnern fur (Sa) haben auch unter drastischeren Bedingungen bisher keine ubersichtlichen Resultate ergeben. Eingegangen am 18. August 1967 [Z 601bl 230 (br.S) 265 (S)
Journal of The American Chemical Society, 2009
The potential energy surfaces of the desulfinylation of prop-2-enesulfinic acid (13) in CH 2 Cl 2... more The potential energy surfaces of the desulfinylation of prop-2-enesulfinic acid (13) in CH 2 Cl 2 solution at -15°C have been explored by quantum calculations and analyzed with kinetic data obtained for the reaction in absence or presence of additives. Monomeric 13 adopts a preferred conformation with gauche SdO/σ(C(1)-C(2) bond pairs and the O-H bond pointing toward C(3). It equilibrates with the more stable dimer (13) 2 (at -15°C) formed by two O-H · · · OdS hydrogen bonds and in which the SdO/ σC(1)-C(2) are gauche also, but the SOH moieties are antiperiplanar with respect to σ(C(1)-C(2)). Dimer (13) 2 undergoes desulfinylation into propene + SO 2 + 13 following a one-step, concerted mechanism. The preferred transition state is a six-membered, chairlike transition structure (C · · · S elongation and S-O · · · H · · · C(3) hydrogen transfer occur in concert) in which the SdO/σ(C(1)-C(2)) bonds are gauche (SdO adopt pseudoaxial positions). There are at least 48 transition states, each one defining a different pathway, all with similar calculated free energies (∆G ‡ ) 25.3-28.6 kcal/mol), which makes the bimolecular (autocatalyzed) retro-ene elimination of SO 2 competing (entropy factor) with a monomolecular process for which the transition state (calculated ∆G ‡ ) 24.3 kcal/mol) implies only one molecule of sulfinic acid. This agrees with the experimental rate law of the reaction which is first order in the concentration of dimer (13) 2 . SO 2 , CF 3 COOH, and BF 3 · Me 2 O do not catalyze the reaction. In the presence of an excess of BF 3 · Me 2 O the desulfinylation is completely inhibited due to the formation of a stable tetramolecular complex of type (CH 2 dCHCH 2 SO 2 H · BF 3 ) 2 (18), for which quantum calculations show that the SdO/σ(C(1)-C(2)) bonds are antiperiplanar whereas the S-OH/σ(C(1)-C(2)) bonds are gauche. Independently of the additive, the retro-ene eliminations of SO 2 are calculated to be concerted and have transition states adopting six-membered cyclic structures in which SdO and σ(C(1)-C(2)) are gauche, the SdO interacting with the additive. Preliminary experiments suggested that the thermodynamically unfavored ene reaction of SO 2 with propene can occur at low temperature using 1 equiv of BF 3 .
Tetrahedron: Asymmetry, 1997
The enantiomerically pure (1S,4R,4'S,5'S)-l-(4',5'-dimethyl-dioxolan-2'yl)-5,6-dimethylidene-7-ox... more The enantiomerically pure (1S,4R,4'S,5'S)-l-(4',5'-dimethyl-dioxolan-2'yl)-5,6-dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene derived from the acetal of furfural and (2S,3S)-butane-2,3-diol underwent addition to 1-acetylvinyl para-nitrobenzoate in the presence of an excess of t-BuMe2SiOSO2CF3 to yield an 83:17 mixture of two diastereomeric products which was converted into (2R)-l,2,3,4-tetrahydro-2-hydroxy-5,8dimethoxynaphthalen-2-yl methyl ketone.
Journal of Organometallic Chemistry, 1979
ABSTRACT
The Journal of Organic Chemistry, 2006
A new straightforward and inexpensive one-pot procedure is described for the preparation of enant... more A new straightforward and inexpensive one-pot procedure is described for the preparation of enantiopure five-membered cyclic nitrones starting from the corresponding lactols. Its efficiency relies on the condensation of unprotected hydroxylamine with readily available lactols and on the chemoselectivity of the subsequent esterification with methanesulfonyl chloride. The targeted enantiomerically pure pyrroline N-oxides are versatile synthetic intermediates: one of the nitrones so-obtained has been converted into new polyhydroxypyrrolizidines, analogues of the alkaloids rosmarinecine and crotanecine, which were assayed for their inhibitory activities toward 22 commercially available glycosidase enzymes. One of them ((-)-7a-epi-crotanecine) is a potent and selective inhibitor of R-mannosidases from jack beans and almonds.
Current Organic Chemistry, 2001
Zaragozic acids (or squalestatins) are very potent inhibitors of squalene synthase. They or simpl... more Zaragozic acids (or squalestatins) are very potent inhibitors of squalene synthase. They or simpler analogs have potential as drugs for lowering the endogenous level of cholesterol in human serum. These compounds are Ras farnesyltransferase inhibitors and might become antitumor drugs. They are also antifungal agents. This account presents synthetic studies subsequent to those reviewed by Nadin and Nicolaou [1]. A wealth of new chemistry has been developed for the generation of highly oxygenated 2,8-dioxabicyclo[3.2.1]octane-3,4,5-tricarboxylic triacids and analogs, so demonstrating the fascination of synthetic chemists for zaragozic acids.
Bioorganic & Medicinal Chemistry Letters, 1999
Radical C-glycosidation of a 3-methylidene-7-oxabicyclo[2.2.1]heptan-2-one derivative with acetob... more Radical C-glycosidation of a 3-methylidene-7-oxabicyclo[2.2.1]heptan-2-one derivative with acetobromomannose gave a ct-C-mannopyranoside that was converted into et-D-ManpCH2(1-~3)-D-GalNAc, a C-disaccharide that inhibits 13-galactosidase from jack bean with IC50 = 9.4 ~tM and K i = 7.5 ~M (mixed mode of inhibition).
Chemical Communications, 1999
A convergent synthesis of (1?2)-and (1?4)-Clinked imino disaccharides was achieved by applying No... more A convergent synthesis of (1?2)-and (1?4)-Clinked imino disaccharides was achieved by applying Nozaki-Kishi coupling of a hydroxyproline-derived carbaldehyde with isolevoglucosenone or levoglucosenone derived enol triflates. Carbohydrate mimetics are potentially useful tools to study cellular interactions, 1 the biosynthesis of glycoproteins, the metabolism of glycoconjugates, 2 and the mechanisms of digestion. 3 Inhibitors of the enzymes involved in these processes such as the glycosidases and the glycosyltransferases are potential anti-cancer, antiviral, and antidiabetic agents, as well as insect antifeedant agents. 4 Disaccharide mimetics such as Cdisaccharides and dideoxyiminoalditol Clinked to monosaccharides have emerged as a new class of specific glycosidase inhibitors and may represent non-hydrolyzable epitopes. 5-7 Recently we disclosed an efficient and versatile approach to the syntheses of (1?3)-C-disaccharides and (1?3)-Clinked imino disaccharides 5 based on the cross-aldolisation of the aldehydes 3 with the nucleophile 1,4-adducts 2 of isolevoglucosenone 1 (Scheme 1). 8,9 We report here that (1?4)-and (1?2)-Cdisaccharides can be prepared starting from 1 and levoglucosenone 17 with 3, respectively. Adduct 6 of benzyl alcohol with isolevoglucosenone was enolized, without elimination of benzylate anion, on treatment with LiHMDS in 95+5 THF-HMPA at 278 °C (Scheme 2). 9 Quenching of the corresponding lithium enolate with 2-[bis(trifluoromethylsulfonyl)amino]-5-chloropyridine provided the enol triflate 7 in 87% yield. 10 Nozaki-Kishi coupling of 7 and aldehyde 8 led to allylic alcohols 9 and 10 isolated in 62 and 17% yield, respectively. 11,12 ‡ Interestingly, the reaction was accelerated by ultrasound and O 2. Under N 2 atmosphere, ultrasound shortened the reaction time from 30 to 2 h. While in the presence of a catalytic amount of O 2 (5 mol% with respect to CrCl 2 , concentration of O 2 lower than 10%), the reaction time was reduced further to less than 1 h. Moreover, O 2 suppressed the formation of 11, resulting from H 2 O quenching of the alkenylchromium species, from 36 to less than 10%.
Bioorganic & Medicinal Chemistry Letters, 2001
Readily derived from d-glucose, 5-[(2R,3S,4R)-3,4-dihydroxypyrrolidin-2-yl]-2-methyl-3-furoic est... more Readily derived from d-glucose, 5-[(2R,3S,4R)-3,4-dihydroxypyrrolidin-2-yl]-2-methyl-3-furoic esters and amides are selective and competitive inhibitors (Ki≥3μM) of α-l-fucosidase from bovine epididymis and from human placenta.