Dynamic equilibriums between pentavalent protonated oxyphosphoranes and their isomeric tetravalent enol phosphonium ions via inter- and intramolecular proton transfer

CASTELIJNS, M. M. C. F.; Schipper, Pieter E.; Aken, van D Dirk; Buck, HM Henk

doi:10.1021/jo00314a010

Cited by 11 publications

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“…For activated experimental model systems as shown in Scheme 3, it could be established with dynamic NMR that the activation parameters for the equilibrium between a and b are ⌬H ϭ 3.0 kcal/mol, T⌬S ϭ Ϫ10.0 kcal/mol, and ⌬G ϭ 13.0 kcal/mol [15]. Also in corresponding model systems we found a dominant T⌬S contribution [15][16][17]. This involves that the phosphonium ion must adopt a special conformation to reach the TS which means that ⌬S can be correlated with the degrees of freedom of the phosphonium ion.…”

Section: Geometries For the S N 2 Reaction Coordinate Of Phosphoryl Tmentioning

confidence: 69%

A linear three‐center four electron bonding identity nucleophilic substitution at carbon, boron, and phosphorus. A theoretical study in combination with van't Hoff modeling

Buck¹

2009

Int J of Quantum Chemistry

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ABSTRACT:We studied various identity nucleophilic substitution reactions based on an S N 2 reaction profile. With calculations and experimental geometries concerning the nature of the various complexes indicated as stable, intermediate, and transition state we were able to show the additional value of van't Hoff 's tetrahedron by changing its geometry via a trigonal pyramid into a trigonal bipyramid. The ratio of the apical and the corresponding tetrahedral bond distance is then 1.333. This value has been used in general as a calibration point for the understanding of the (in)stabilities of the complex formation on the S N 2 reaction coordinate. The relevance of this approach has been also proved for enzymatic reactions focused on carbon and phosphorus substrates. Furthermore, it could be established that identity proton-in-line displacements are fully comparable with the relocation of carbon in a nucleophilic substitution reaction as Cl Ϫ ϩ CH 3 Cl. The significance of this information will afford new insight in the dynamics of a linear three-center four-electron complex.

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Section: Geometries For the S N 2 Reaction Coordinate Of Phosphoryl Tmentioning

confidence: 69%

A linear three‐center four electron bonding identity nucleophilic substitution at carbon, boron, and phosphorus. A theoretical study in combination with van't Hoff modeling

Buck¹

2009

Int J of Quantum Chemistry

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“…Intermediates 1 were designed to behave as cyclic 1,3-dipoles, related to Sydnones , and Münchnones, but can alternatively be formulated as phosphonium ylides. Phosphonium ions are known to cyclize to phosphoranes when γ-alkoxide groups are present, and similar interactions involving γ-keto groups have also been invoked to explain the catalysis of certain aldol reactions by phosphines. Accordingly, 1 may potentially exist in either a cyclic form “ cyc - 1 ” or an acyclic form “ acyc - 1 ”.…”

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confidence: 99%

Cyclic 1,3-Dipoles or Acyclic Phosphonium Ylides? Electronic Characterization of “Montréalones”

et al. 2008

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The structural features of a recently introduced class of 1,3-dipolar reagents have been computed by density functional theory and ab initio methods. The reagents are formally derived from Münchnones by replacement of the C O group with a PR3 unit. The parent species (PR3 = PH3) shows a long P...O interaction (2.55 A at the B3LYP/6-31+G(d) level), together with a nonplanar ring, and is best described as a weakly chelated acylamino-phosphonium ylide. The corresponding acyclic form, in which the P...O interaction is absent, is predicted to be 2-3 kcal mol-1 higher in enthalpy. Variation of the phosphorus substituents exerts a marked effect on the P...O distance, with electron-withdrawing groups favoring a covalent interaction [P...O 1.97 A for PR3 = PPh(catechyl)] and electron-donating groups favoring a weak interaction [P...O 3.92 A for PR3 = PPh3]. However, this variation has little effect on the relative energies of the cyclic and acyclic forms. The barriers for concerted cycloadditions with ethylene are 22.8 kcal mol-1 (PH3), 31.7 kcal mol-1 (PPh3), and 16.2 kcal mol-1 [PPh(catechyl) with axial O], which correspond with experimental observations and follow the same trend as the energies required to distort the dipole to the TS geometry.

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“…The peak m / z 893 is in agreement with 14 , characterized by the two phosphorus set of signals at 76 and 51 ppm in 31 P NMR spectra collected in chloroform. This species exists, according to NMR results, both in the open keto- and in the cyclic eno- tautomer 17 , in larger amount in toluene than in chloroform, and comes from a subsequent addition of phosphine to the exocyclic double bond of the phosphorane intermediate. It can further lose ethanol under the MS conditions, giving the 15 ( m / z 847).…”

Section: Analytical Techniques For the Elucidation Of Step 2bmentioning

confidence: 88%

The Synthesis of GV143253A: A Case Study for the Use of Analytical and Statistical Tools to Elucidate the Reaction Mechanism and to Optimize the Process

Guercio

Perboni

Tinazzi

et al. 2010

Org. Process Res. Dev.

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GV143253A 1 is a broad-spectrum injectable β-lactam belonging to the class of trinem antibiotics. This article describes the work which enabled a detailed process understanding via several analytical techniques and the subsequent optimization of a key intermediate. By means of a combined application of 31 P NMR spectroscopy and MS spectrometry, the main impurities have been identified and the reaction mechanisms clarified. Moreover, a design of experiments (DoE) approach was applied which substantially improved the overall yield.

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Dynamic equilibriums between pentavalent protonated oxyphosphoranes and their isomeric tetravalent enol phosphonium ions via inter- and intramolecular proton transfer

Cited by 11 publications

References 1 publication

A linear three‐center four electron bonding identity nucleophilic substitution at carbon, boron, and phosphorus. A theoretical study in combination with van't Hoff modeling

A linear three‐center four electron bonding identity nucleophilic substitution at carbon, boron, and phosphorus. A theoretical study in combination with van't Hoff modeling

Cyclic 1,3-Dipoles or Acyclic Phosphonium Ylides? Electronic Characterization of “Montréalones”

The Synthesis of GV143253A: A Case Study for the Use of Analytical and Statistical Tools to Elucidate the Reaction Mechanism and to Optimize the Process

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