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Anuradha Varshney - One of the best experts on this subject based on the ideXlab platform.

  • p nitrobenzyltriphenyl Phosphonium Ylide initiated radical terpolymerization of styrene methyl methacrylate and acrylonitrile synthesis characterization and properties
    Polymer International, 2007
    Co-Authors: Kiran Prajapati, Anuradha Varshney
    Abstract:

    Solution terpolymerization of styrene (St), methyl methacrylate (MMA) and acrylonitrile (AN) was carried out in dioxane at 65 ± 0.1 °C for 120 min using p-nitrobenzyltriphenyl Phosphonium Ylide as radical initiator. The kinetic expression is as follows (Rp is the rate of polymerization): Rp∝ [Ylide]0.45[St]0.8[MMA]1.2[AN]1.2. The overall activation energy is 42 kJ mol−1 L−1. The composition of terpolymer, calculated from 1H NMR and elemental analysis, was used to evaluate reactivity ratio, as r1 (MMA + AN) = 0.06 and r2 (St) = 0.005, employing the Kelen–Tudos method. It confirmed the alternating nature of the terpolymer. The terpolymer was characterized using 13C NMR, gel permeation chromatography and thermogravimetric differential thermal analysis. Electron spin resonance spectroscopy confirmed the presence of the phenyl radical responsible for initiation. Copyright © 2006 Society of Chemical Industry

  • Free Radical Polymerisation of Methylmethacrylate Using p-nitrobenzyltriphenyl Phosphonium Ylide as Novel Initiator
    Journal of Polymer Research, 2006
    Co-Authors: Kiran Prajapati, Anuradha Varshney
    Abstract:

    p -nitrobenzyl triphenyl Phosphonium Ylide initiated radical polymerisation of MMA in 1-4 dioxane at 65 ± 1°C for 2 h under a nitrogen blanket, follows ideal kinetics with bimolecular termination. The overall activation energy and average value of k _p ^2/ k _t are 75.7 kJ mol and 1.14 × 10^2 l mol^−1 s^−1. FTIR Spectroscopy confirms a band of 1,729 cm^−1 of the ester group. ^1H NMR and ^13C NMR confirms methoxy protons at 3.8 δ ppm and 52 δ ppm, respectively. E.S.R studies confirm a free radical mode of polymerisation. TGDTA analysis confirms the atactic nature of polymer and its thermal stability up to 120°C. Ylide dissociates to give a phenyl radical which is responsible for polymerisation.

  • Terpene-based semi-interpenetrating polymer networks initiated by p-nitrobenzyl triphenyl Phosphonium Ylide: synthesis and characterization
    Designed Monomers and Polymers, 2006
    Co-Authors: Kiran Prajapati, Anuradha Varshney
    Abstract:

    A series of semi-interpenetrating polymer networks (IPNs) based on poly(α-terpineol-costyrene) and ethylacrylate cross-linked with divinyl benzene have been synthesized at 80°C for 80 min in dioxane, initiated by p-nitrobenzyl triphenyl Phosphonium Ylide, under an inert atmosphere of nitrogen. The Fourier transform infrared spectrum attributes structural evidences for IPNs, indicating characteristic frequencies of the ester group of ethyl acrylate at 1727 cm−1 and alcoholic group of α-terpineol at 3390 cm−1. The percentage swelling and average molecular weight between cross-links (m c) are a direct function of α-terpineol-co-styrene and p-nitrobenzyl triphenyl Phosphonium Ylide and inverse function of ethyl acrylate and divinylbenzene. The semi-IPN system is confirmed by two T g values from the differential scanning calorimetry scan at 15 and 59°C. SEM micrographs show phase separation. The thermogravimetric analysis (TGA) curve shows the IPN to be thermally stable. From the TGA curve the activation energ...

  • p‐Nitrobenzyltriphenyl Phosphonium Ylide‐initiated radical terpolymerization of styrene, methyl methacrylate and acrylonitrile: synthesis, characterization and properties
    Polymer International, 2006
    Co-Authors: Kiran Prajapati, Anuradha Varshney
    Abstract:

    Solution terpolymerization of styrene (St), methyl methacrylate (MMA) and acrylonitrile (AN) was carried out in dioxane at 65 ± 0.1 °C for 120 min using p-nitrobenzyltriphenyl Phosphonium Ylide as radical initiator. The kinetic expression is as follows (Rp is the rate of polymerization): Rp∝ [Ylide]0.45[St]0.8[MMA]1.2[AN]1.2. The overall activation energy is 42 kJ mol−1 L−1. The composition of terpolymer, calculated from 1H NMR and elemental analysis, was used to evaluate reactivity ratio, as r1 (MMA + AN) = 0.06 and r2 (St) = 0.005, employing the Kelen–Tudos method. It confirmed the alternating nature of the terpolymer. The terpolymer was characterized using 13C NMR, gel permeation chromatography and thermogravimetric differential thermal analysis. Electron spin resonance spectroscopy confirmed the presence of the phenyl radical responsible for initiation. Copyright © 2006 Society of Chemical Industry

  • Free‐radical polymerization of styrene with p‐nitrobenzyl triphenyl Phosphonium Ylide as an initiator
    Journal of Polymer Science Part A: Polymer Chemistry, 2005
    Co-Authors: Kiran Prajapati, Anuradha Varshney
    Abstract:

    The free-radical polymerization of styrene with p-nitrobenzyl triphenyl Phosphonium Ylide as an initiator in dioxane at 80 ± 1 °C in a dilatometer under a nitrogen atmosphere for 150 min resulted in a syndiotactic polymer, as evidenced by IR, 1H NMR, and 13C NMR spectroscopy. A 1H NMR spectrum showed methylene protons as triplets; 13C NMR signals of the phenyl ipso carbons were used for the determination of the tacticity. The system followed ideal kinetics. Gel permeation chromatography data were used evaluate the weight-average molecular weight. The overall activation energy was 47 kJ/mol. Electron spin resonance spectroscopy confirmed the initiation by the phenyl radical obtained by the dissociation of the Ylide and the free-radical mode of polymerization. Differential scanning calorimetry studies showed the glass-transition temperature of the polymer to be 342 K. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6524–6533, 2005

Yves Canac - One of the best experts on this subject based on the ideXlab platform.

  • NHC Core Phosphonium Ylide-based Palladium(II) Pincer Complexes: The Second Ylide Extremity Makes the Difference.
    Inorganic Chemistry, 2020
    Co-Authors: Rachid Taakili, Christine Lepetit, Cécile Barthes, Amel Goëffon, Carine Duhayon, Dmitry A. Valyaev, Yves Canac
    Abstract:

    The coordinating properties of N-heterocyclic carbene (NHC) (A), phenolate (B), and Phosphonium Ylide (C) moieties were investigated systematically through the preparation of a family of NHC, Phosphonium Ylide-based pincer ligands, where the third donor extremity can be either an NHC, a phenolate, or a Phosphonium Ylide. The overall donor character of such ligands [NHC(AaBbCc)] (a + b + c = 2) was analyzed by comparison of the molecular orbitals (energy and shape), oxidation potentials (Epox), and IR νCO and νCN stretching frequencies of their isostructural pincer Pd(II) complexes [NHC(AaBbCc)PdL][OTf] (L = NCCH3, CO, or CNtBu). The three categories of pincer complexes based on Phosphonium Ylides were easily obtained by acidic treatment of their highly stable ortho-metalated Pd(II) precursors prepared in a single step from readily available N-phosphonio-substituted imidazolium salts. Analysis of IR data indicated that NHC and phenolate ligands have a similar donor character but which remains lower than that of the Phosphonium Ylide. The impact on catalytic performance of the incorporation of a second strongly donating Phosphonium Ylide into the ligand architecture was illustrated in the Pd-catalyzed allylation of aldehydes.

  • NHC Core Pincer Ligands Exhibiting Two Anionic Coordinating Extremities
    Molecules, 2020
    Co-Authors: Rachid Taakili, Yves Canac
    Abstract:

    The chemistry of NHC core pincer ligands of LX2 type bearing two pending arms, identical or not, whose coordinating center is anionic in nature, is here reviewed. In this family, the negative charge of the coordinating atoms can be brought either by a carbon atom via a Phosphonium Ylide (R3P+–CR2−) or by a heteroatom through amide (R2N−), oxide (RO−), or thio(seleno)oxide (RS−, RSe−) donor functionalities. Through selected examples, the synthetic methods, coordination properties, and applications of such tridentate systems are described. Particular emphasis is placed on the role of the donor ends in the chemical behavior of these species.

  • Palladium( ii ) pincer complexes of a C , C , C -NHC, diPhosphonium bis(Ylide) ligand
    Dalton Transactions, 2019
    Co-Authors: Rachid Taakili, Christine Lepetit, Carine Duhayon, Dmitry Valyaev, Noël Lugan, Yves Canac
    Abstract:

    A new family of pincer palladium(ii) complexes bearing an electron-rich C,C,C-NHC, diPhosphonium bis(Ylide) ligand of LX2-type was prepared through the dual N-functionalization of 1H-imidazole by (3-bromopropyl)triphenylPhosphonium bromide. Selected basic conditions allowed the sequential coordination of the NHC and Phosphonium Ylide moieties to Pd(ii). This strategy led to an original ortho-metallated complex where the Pd center is bonded to four carbon atoms of three different natures: carbenic (sp2), arylic (sp2), and chiral ylidic (sp3). Protonation of the latter afforded NHC, diPhosphonium bis(Ylide) pincer Pd(ii) complexes as a mixture of meso- and dl-diastereomers (de = 50%). The selectivity of C-coordination was rationalized on the basis of DFT calculations, evidencing the quasi-degeneracy of the two diastereomeric forms.

  • Phosphine-NHC Manganese Hydrogenation Catalyst Exhibiting a Non-Classical Metal-Ligand Cooperative H Activation Mode
    Angewandte Chemie International Edition, 2019
    Co-Authors: Ruqaya Buhaibeh, Carine Duhayon, Dmitry A. Valyaev, Yves Canac, Noël Lugan, Oleg A Filippov, Antoine Bruneau-voisine, Jérémy Willot, Jean-baptiste Sortais
    Abstract:

    Deprotonation of the Mn NHC-phosphine complex fac-[MnBr(CO) (κ P,C-Ph PCH NHC)] (2) under a H atmosphere readily gives the hydride fac-[MnH(CO) (κ P,C-Ph PCH NHC)] (3) via the intermediacy of the highly reactive 18-e NHC-phosphinomethanide complex fac-[Mn(CO) (κ P,C,C-Ph PCHNHC)] (6 a). DFT calculations revealed that the preferred reaction mechanism involves the unsaturated 16-e mangana-substituted Phosphonium Ylide complex fac-[Mn(CO) (κ P,C-Ph P=CHNHC)] (6 b) as key intermediate able to activate H via a non-classical mode of metal-ligand cooperation implying a formal λ -P-λ -P phosphorus valence change. Complex 2 is shown to be one of the most efficient pre-catalysts for ketone hydrogenation in the Mn series reported to date (TON up to 6200).

  • A convenient access to N-phosphonio-substituted NHC metal complexes [M = Ag(i), Rh(i), Pd(ii)]
    Dalton Transactions, 2017
    Co-Authors: Idir Benaissa, Rachid Taakili, N. Lugan, Yves Canac
    Abstract:

    A series of NHC pre-ligands featuring a pendant Phosphonium moiety attached to N[prime or minute] position through a propyl linker was readily obtained upon quaternization of N-mesityl- and N-methyl-imidazole, or N-mesityl-imidazoline using (3-bromo-propyl)-triphenylPhosphonium bromide. Reactions of the resulting dicationic salts with [PdCl(allyl)]2 in the presence of K2CO3 afforded the anticipated NHC-ligated Pd(ii) metal complexes in high yields. Further treatment of the latter complexes with tBuOK induced a deprotonation of the carbon atom adjacent to the Phosphonium moiety and the formation of the corresponding C,C-chelating NHC-Phosphonium Ylide Pd(ii) complexes. Investigation of an alternative synthetic route involving a silver transmetallation reaction incidentally allowed isolation and full characterization of an unusual dimeric tetranuclear NHC Ag(i) complex of general formula [(NHC[similar]P+)2(Ag4Br6)2-].

Remi Chauvin - One of the best experts on this subject based on the ideXlab platform.

  • olefin metathesis with ru based catalysts exchanging the typical n heterocyclic carbenes by a phosphine Phosphonium Ylide
    Catalysts, 2017
    Co-Authors: Laia Arnedo Marimon, Remi Chauvin, Albert Poater Teixidor
    Abstract:

    Albert Poater thanks the Spanish Ministry of Economy and Competitiveness (MINECO) for a project CTQ2014-59832-JIN and Xarxa de Quimica Teorica i Computacional for a VALCHEM2016 project

  • Olefin Metathesis with Ru-Based Catalysts Exchanging the Typical N-Heterocyclic Carbenes by a Phosphine–Phosphonium Ylide
    Catalysts, 2017
    Co-Authors: Laia Arnedo, Remi Chauvin, Albert Poater
    Abstract:

    Density functional theory (DFT) calculations have been used to describe the first turnover of an olefin metathesis reaction calling for a new in silico family of homogenous Ru-based catalysts bearing a phosphine–Phosphonium Ylide ligand, with ethylene as a substrate. Equal to conventional Ru-based catalysts bearing an N-heterocyclic carbene (NHC) ligand, the activation of these congeners occurs through a dissociative mechanism, with a more exothermic first phosphine dissociation step. In spite of a stronger electron-donating ability of a Phosphonium Ylide C-ligand with respect to a diaminocarbene analogue, upper energy barriers were calculated to be on average ca. 5 kcal/mol higher than those of Ru–NHC standards. Overall, the study also highlights advantages of bidentate ligands over classical monodentate NHC and phosphine ligands, with a particular preference for the cis attack of the olefin. The new generation of catalysts is constituted by cationic complexes potentially soluble in water, to be compared with the typical neutral Ru–NHC onesAlbert Poater thanks the Spanish Ministry of Economy and Competitiveness (MINECO) for a project CTQ2014-59832-JIN and Xarxa de Química Teòrica i Computacional for a VALCHEM2016 projec

  • Olefin Metathesis with Ru-Based Catalysts Exchanging the Typical N-Heterocyclic Carbenes by a Phosphine–Phosphonium Ylide
    MDPI AG, 2017
    Co-Authors: Laia Arnedo, Remi Chauvin, Albert Poater
    Abstract:

    Density functional theory (DFT) calculations have been used to describe the first turnover of an olefin metathesis reaction calling for a new in silico family of homogenous Ru-based catalysts bearing a phosphine–Phosphonium Ylide ligand, with ethylene as a substrate. Equal to conventional Ru-based catalysts bearing an N-heterocyclic carbene (NHC) ligand, the activation of these congeners occurs through a dissociative mechanism, with a more exothermic first phosphine dissociation step. In spite of a stronger electron-donating ability of a Phosphonium Ylide C-ligand with respect to a diaminocarbene analogue, upper energy barriers were calculated to be on average ca. 5 kcal/mol higher than those of Ru–NHC standards. Overall, the study also highlights advantages of bidentate ligands over classical monodentate NHC and phosphine ligands, with a particular preference for the cis attack of the olefin. The new generation of catalysts is constituted by cationic complexes potentially soluble in water, to be compared with the typical neutral Ru–NHC ones

  • Towards the stability limit of cyclic diPhosphonium bis-Ylides
    Comptes Rendus Chimie, 2010
    Co-Authors: Mohammed Abdalilah, Christine Lepetit, Yves Canac, Remi Chauvin
    Abstract:

    A typology of molecules containing two Phosphonium Ylide groups (bis-Ylides) is proposed, versus the bridge length (fused, ω- and α-bisYlides) and their relative topographical orientations (head-to-head, tail-to-tail or head-to-tail). The formal electrostatic constraint occurring in the head-to-head series is systematically addressed for cyclic representatives based on the o-bis(diphenylphosphonio)benzene framework. After a survey of previously reported results in the fused and β-bis-Ylide series, emphasis is given to the cyclic α-bis-Ylides. The non-substituted, non-stabilized version escaped isolation through spontaneous fragmentation to bis(diphenylphosphino)benzene and acetylene. Inspired by this result, the reverse process was employed for the generation of stabilized representatives with ethoxycarbonyl and benzoyl substituents at the ylidic carbon atoms. The stability and stereochemistry of the obtained head-to-head α-bis-Ylides was investigated by NMR techniques and reproduced and analyzed by DFT calculations. The role of electrostatics in determining structural and reactivity features of cyclically constrained species is here illustrated.

  • Phosphino-(α-sulfinylalkyl)Phosphonium Ylide complexes (Rh, Pd) with a configurationally stable asymmetric ylidic carbon
    Tetrahedron-asymmetry, 2010
    Co-Authors: Remigiusz Zurawinski, Christine Lepetit, Yves Canac, Marian Mikołajczyk, Laure Vendier, Remi Chauvin
    Abstract:

    Abstract The synthesis and structure of Rh(I) and Pd(II) complexes of chiral P,C-chelating phosphino-(α-sulfinylalkyl)Phosphonium Ylide ligands with a trisubstituted asymmetric ylidic center P + –C∗R(S∗(O) p -Tol)–M (R = alkyl group) have been investigated, and compared to those of the analogous disubstituted Ylide complexes (R = H). Reaction of the ethyl onium Ylide of o -bis(diphenylphosphino)benzene with (−)-menthyl-( S )- p -tolylsulfinate afforded the corresponding racemic erythro phosphino-(α-sulfinylethyl)Phosphonium in 90% de (R = Me). The racemization process is interpreted by a Berry-like pseudorotation mechanism driven by the steric repulsion between the α-methyl substituent and the bulky menthyloxy S-substituent or sulfur lone pair in the intermediate Ylide-sulfinyl adduct. The Ylide of phosphino-(α-sulfinylethyl)Phosphonium reacts with [Rh(cod) 2 ][PF 6 ] and PdCl 2 (MeCN) 2 to afford the corresponding P,C∗-chelated threo -Rh(I) and erythro -Pd(II) mononuclear complexes in 70% yield and total diastereoselectivity. These respective complexes act as efficient catalytic precursors for the hydrogenation of ( Z )-α-acetamidocinnamic acid and allylic substitution of 3-acetoxy-1,3-diphenyl-1-propene with sodium dimethyl malonate. The bonding features of the erythro -Pd(II) complex exhibiting a sulfinyl O⋯Pd interaction are studied theoretically at the DFT level using ELF and MESP analyses. The η 2 -P,C haptomeric form of the Ylide ligand is estimated to compete at 19% with the η 1 -C haptomeric form dominating at 81%.

Kiran Prajapati - One of the best experts on this subject based on the ideXlab platform.

  • p nitrobenzyltriphenyl Phosphonium Ylide initiated radical terpolymerization of styrene methyl methacrylate and acrylonitrile synthesis characterization and properties
    Polymer International, 2007
    Co-Authors: Kiran Prajapati, Anuradha Varshney
    Abstract:

    Solution terpolymerization of styrene (St), methyl methacrylate (MMA) and acrylonitrile (AN) was carried out in dioxane at 65 ± 0.1 °C for 120 min using p-nitrobenzyltriphenyl Phosphonium Ylide as radical initiator. The kinetic expression is as follows (Rp is the rate of polymerization): Rp∝ [Ylide]0.45[St]0.8[MMA]1.2[AN]1.2. The overall activation energy is 42 kJ mol−1 L−1. The composition of terpolymer, calculated from 1H NMR and elemental analysis, was used to evaluate reactivity ratio, as r1 (MMA + AN) = 0.06 and r2 (St) = 0.005, employing the Kelen–Tudos method. It confirmed the alternating nature of the terpolymer. The terpolymer was characterized using 13C NMR, gel permeation chromatography and thermogravimetric differential thermal analysis. Electron spin resonance spectroscopy confirmed the presence of the phenyl radical responsible for initiation. Copyright © 2006 Society of Chemical Industry

  • Free Radical Polymerisation of Methylmethacrylate Using p-nitrobenzyltriphenyl Phosphonium Ylide as Novel Initiator
    Journal of Polymer Research, 2006
    Co-Authors: Kiran Prajapati, Anuradha Varshney
    Abstract:

    p -nitrobenzyl triphenyl Phosphonium Ylide initiated radical polymerisation of MMA in 1-4 dioxane at 65 ± 1°C for 2 h under a nitrogen blanket, follows ideal kinetics with bimolecular termination. The overall activation energy and average value of k _p ^2/ k _t are 75.7 kJ mol and 1.14 × 10^2 l mol^−1 s^−1. FTIR Spectroscopy confirms a band of 1,729 cm^−1 of the ester group. ^1H NMR and ^13C NMR confirms methoxy protons at 3.8 δ ppm and 52 δ ppm, respectively. E.S.R studies confirm a free radical mode of polymerisation. TGDTA analysis confirms the atactic nature of polymer and its thermal stability up to 120°C. Ylide dissociates to give a phenyl radical which is responsible for polymerisation.

  • Terpene-based semi-interpenetrating polymer networks initiated by p-nitrobenzyl triphenyl Phosphonium Ylide: synthesis and characterization
    Designed Monomers and Polymers, 2006
    Co-Authors: Kiran Prajapati, Anuradha Varshney
    Abstract:

    A series of semi-interpenetrating polymer networks (IPNs) based on poly(α-terpineol-costyrene) and ethylacrylate cross-linked with divinyl benzene have been synthesized at 80°C for 80 min in dioxane, initiated by p-nitrobenzyl triphenyl Phosphonium Ylide, under an inert atmosphere of nitrogen. The Fourier transform infrared spectrum attributes structural evidences for IPNs, indicating characteristic frequencies of the ester group of ethyl acrylate at 1727 cm−1 and alcoholic group of α-terpineol at 3390 cm−1. The percentage swelling and average molecular weight between cross-links (m c) are a direct function of α-terpineol-co-styrene and p-nitrobenzyl triphenyl Phosphonium Ylide and inverse function of ethyl acrylate and divinylbenzene. The semi-IPN system is confirmed by two T g values from the differential scanning calorimetry scan at 15 and 59°C. SEM micrographs show phase separation. The thermogravimetric analysis (TGA) curve shows the IPN to be thermally stable. From the TGA curve the activation energ...

  • p‐Nitrobenzyltriphenyl Phosphonium Ylide‐initiated radical terpolymerization of styrene, methyl methacrylate and acrylonitrile: synthesis, characterization and properties
    Polymer International, 2006
    Co-Authors: Kiran Prajapati, Anuradha Varshney
    Abstract:

    Solution terpolymerization of styrene (St), methyl methacrylate (MMA) and acrylonitrile (AN) was carried out in dioxane at 65 ± 0.1 °C for 120 min using p-nitrobenzyltriphenyl Phosphonium Ylide as radical initiator. The kinetic expression is as follows (Rp is the rate of polymerization): Rp∝ [Ylide]0.45[St]0.8[MMA]1.2[AN]1.2. The overall activation energy is 42 kJ mol−1 L−1. The composition of terpolymer, calculated from 1H NMR and elemental analysis, was used to evaluate reactivity ratio, as r1 (MMA + AN) = 0.06 and r2 (St) = 0.005, employing the Kelen–Tudos method. It confirmed the alternating nature of the terpolymer. The terpolymer was characterized using 13C NMR, gel permeation chromatography and thermogravimetric differential thermal analysis. Electron spin resonance spectroscopy confirmed the presence of the phenyl radical responsible for initiation. Copyright © 2006 Society of Chemical Industry

  • Free‐radical polymerization of styrene with p‐nitrobenzyl triphenyl Phosphonium Ylide as an initiator
    Journal of Polymer Science Part A: Polymer Chemistry, 2005
    Co-Authors: Kiran Prajapati, Anuradha Varshney
    Abstract:

    The free-radical polymerization of styrene with p-nitrobenzyl triphenyl Phosphonium Ylide as an initiator in dioxane at 80 ± 1 °C in a dilatometer under a nitrogen atmosphere for 150 min resulted in a syndiotactic polymer, as evidenced by IR, 1H NMR, and 13C NMR spectroscopy. A 1H NMR spectrum showed methylene protons as triplets; 13C NMR signals of the phenyl ipso carbons were used for the determination of the tacticity. The system followed ideal kinetics. Gel permeation chromatography data were used evaluate the weight-average molecular weight. The overall activation energy was 47 kJ/mol. Electron spin resonance spectroscopy confirmed the initiation by the phenyl radical obtained by the dissociation of the Ylide and the free-radical mode of polymerization. Differential scanning calorimetry studies showed the glass-transition temperature of the polymer to be 342 K. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6524–6533, 2005

Iwao Yamamoto - One of the best experts on this subject based on the ideXlab platform.

  • Diastereoselective Synthesis of a Hydroazulene Derivative by Tandem Michael-Wittig Reactions
    Phosphorus Sulfur and Silicon and the Related Elements, 2002
    Co-Authors: Tomoko Nagao, Tetsuya Fujimoto, Masayoshi Isozaki, Iwao Yamamoto
    Abstract:

    The reaction of a cyclic Phosphonium Ylide [ 1 ] with enoate 2 gives a hydroazulene derivative with stereoselectivity.

  • Diastereoselective tandem Michael-intramolecular Wittig reactions of a cyclic Phosphonium Ylide with 8-phenylmenthyl enoates.
    The Journal of Organic Chemistry, 2001
    Co-Authors: Tomoko Nagao, Akikazu Kakehi, Iwao Yamamoto, Tetsuya Fujimoto, Takanori Suenaga, Takao Ichihashi, Ryozo Iriye
    Abstract:

    The diastereoselective tandem Michael−intramolecular Wittig reactions of a five-membered cyclic Phosphonium Ylide 2 using 8-phenylmenthyl enoates were examined. The reaction of the Phosphonium Ylide with 8-phenylmenthyl cinnamate followed by the hydrolysis of the resulting enol ether 4a afforded (3R,4S)-4-(diphenylphosphinyl)-3-phenylcycloheptanone (3R,4S)-5a as the major isomer. The diastereoselectivity of the initial tandem reactions was estimated to be 94:6 from the 31P NMR of a mixture of the diastereomeric ketal derivatives 6a and 6‘a which were obtained by the reaction of 5a with (2R,3R)-2,3-butanediol, and the absolute configuration of the major isomer was determined by the single-crystal X-ray analysis. Similar reactions using some 8-phenylmenthyl alkenoates were attempted. As a result, it was clarified that the corresponding trans-ketones 5b−d were obtained and that the diastereomer ratios of their ketal derivatives were 60:40−73:27.

  • Reaction of a Cyclic Phosphonium Ylide with α,β-Unsaturated Thioesters
    The Journal of Organic Chemistry, 1999
    Co-Authors: Narumi Kishimoto, Tetsuya Fujimoto, Iwao Yamamoto
    Abstract:

    The tandem Michael−intramolecular Wittig reactions of a five-membered cyclic Phosphonium Ylide (2) with α,β-unsaturated thioesters afforded cycloheptene derivatives 4a−g in 29−58% yield. The reaction proceeded via a rigid phosphabicyclic intermediate and supplied the cycloheptene derivatives with high stereoselectivity. On the other hand, although the reaction using S-cyclohexyl cyclopentenethiocarboxylate 5a as a substrate gave a 1:1 mixture of cis and trans adducts of the corresponding hydroazulene derivatives, the reaction of S-tert-butyl cyclopentenethiocarboxylate 5b gave cis-adduct as a major product (cis:trans =17:3).

  • synthesis of seven membered cyclic enol ether derivatives from the reaction of a cyclic Phosphonium Ylide with α β unsaturated esters
    Journal of Organic Chemistry, 1997
    Co-Authors: Tetsuya Fujimoto, Yohichi Kodama, Iwao Yamamoto, Akikazu Kakehi
    Abstract:

    The tandem Michael−intramolecular Wittig reactions of a five-membered cyclic Phosphonium Ylide (2) with α,β-unsaturated esters afforded seven-membered cyclic enol ether derivatives 4a−e in 37−73% yield. The reaction proceeded via a rigid phosphabicyclic intermediate and supplied the enol ether derivatives with high stereoselectivity. On the other hand, the reaction using ethyl acrylate as a substrate gave the 1:3 adduct 15 of the Ylide and the enoate via the repetition of the Michael-type addition and regeneration of the Ylide followed by the intramolecular Wittig reaction.