Stereoselectivity in fragmentation and rearrangement of α-hydroxyimino-phosphinates and -phosphonates. A synthetic approach to acylphosphon- and phosphor-amidates. Crystal structures of methyl (E)-α-hydroxyimino-benzylphenylphosphinate and methyl benzoylphenylphosphonamidate

Breuer, Eli; Schlossman, Ada; Safadi, Muhammad; Gibson, Dan; Chorev, Michael; Leader, Haim

doi:10.1039/p19900003263

Cited by 25 publications

(8 citation statements)

References 10 publications

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“…Thus, the most unusual feature of the present reaction is the spontaneous departure of the OH at room temperature. This resembles the Beckmann rearrangements we reported recently, , in which the departure of the OH group took place without the customary acid catalysis. In the present case as well as in the Beckmann rearrangements, OMe derivatives reacted much more sluggishly.…”

Section: Resultssupporting

confidence: 88%

Spontaneous Lossen Rearrangement of (Phosphonoformyl)hydroxamates. The Migratory Aptitude of the Phosphonyl Group

Salomón

Breuer

1997

J. Org. Chem.

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(i-PrO)2P(O)COSEt (1) reacted with NH2OH in pyridine at room temperature to give mainly (i-PrO)2P(O)NH2 (4). The formation of 4 was interpreted in terms of a spontaneous Lossen rearrangement of (i-PrO)2P(O)CONHOH (2a) formed in the reaction. A transient 31P NMR signal appearing in the reaction mixture at δ −1.8 was assigned to 2a. Trapping of (i-PrO)2P(O)NCO (5), formed in the reaction of 1 and NH2OH, by cyclohexylamine gave (i-PrO)2P(O)NHCONHC6H11 (6). Attempted isolation of 6 gave the hydrolyzed product N-cyclohexylurea (7). The reaction of 1 with NH2OMe proceeded slower than that with NH2OH and gave the expected (i-PrO)2P(O)CONHOMe (2b), which was isolated and identified. 2b converts slowly to 4 in pyridine at room temperature. In contrast, MeNHOH reacted rapidly with 1 and gave the stable crystalline (i-PrO)2P(O)CON(Me)OH (2c). The structure of hydroxamates 2 were assigned on the basis of 1H, 13C, and 31P NMR spectral data. This facile Lossen rearrangement is discussed in terms of the unusually high migratory aptitude of the phosphonyl group.

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Section: Resultssupporting

confidence: 88%

Spontaneous Lossen Rearrangement of (Phosphonoformyl)hydroxamates. The Migratory Aptitude of the Phosphonyl Group

Salomón

Breuer

1997

J. Org. Chem.

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“…Bond distances and angles are within the range of those reported for related amide and phosphine derivatives. Note, however, that the P-N bond (1.728(2) Å) is longer than that found in PhP(O)(OMe)NHC(O)Ph (1.674 Å) 21 and in (MeO)P(O)(SMe)NHC(O)Me (1.641 Å) 22 and similar to that of Ph 2 P(S)NHC(O)Ph (1.72(1)Å). 23 The P-N-C(13) bond angle (122.3(1)Њ) is more obtuse than the P-C-C angle found in Ph 2 PCH 2 CO 2 Et (113.24Њ) 24 and Ph 2 PCH 2 CO 2 H (110.188Њ).…”

Section: Crystal Structures Of 1 and 12bmentioning

confidence: 69%

Coordination properties of novel hemilabile acetamide-derived P,O phosphine ligands. Crystal structures of Ph2PNHC(O)Me and [PdMe{PPh2NHC(O)Me}{PPh2NHC(O)Me}][O3SCF3] †

Braunstein

Frison

Morise

et al. 2000

J. Chem. Soc., Dalton Trans.

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Cationic methyl Pd() complexes are described in which the new heterofunctional phosphine ligands Ph 2 PNHC(O)Me 1 or Ph 2 PN(Me)C(O)Me 3 behave as rigid and/or hemilabile P,O chelates. The chelating ability of 3 is higher than that of 1 and both are compared to that of other P,O ligands, such as the keto-and amido-phosphines Ph 2 PCH 2 C(O)Ph and Ph 2 PCH 2 C(O)NPh 2 , respectively. The crystal structure of 1 reveals the presence in the solid-state of an intermolecular hydrogen-bonded network N-H ؒ ؒ ؒ O and that of12b establishes the presence of both a chelating and a monodentate ligand 1 in the same complex. Carbonylation of the cationic methyl complexes 8a, 17, 18a and 20a afforded the corresponding acetyl complexes in which this ligand occupies a position cis to phosphorus, irrespective of that of the alkyl ligand in the precursor complex.

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“…32, 33 A well known complication of the Beckmann rearrangement is the Beckmann fragmentation, also referred to as the "abnormal" Beckmann reaction. This occurs usually in cases in which the migrating groups have a tendency to form stable carbocations, which split off as such, instead of migrating from the C to N. 33 In a series of previous papers from our laboratory, over the past decade, we have reported that α-hydroxyiminophosphonate diesters, 34 α-hydroxyiminophosphinate, 34 and α-hydroxyiminophosphonamidate 35 monoesters undergo facile Beckmann rearrangement upon heating. In contrast, acidic α-hydroxyiminophosphonate monoesters (e.g.…”

Section: Discussionmentioning

confidence: 99%

Fragmentation of methyl hydrogen α-hydroxyiminobenzylphosphonates — kinetics, mechanism and the question of metaphosphate formation †

Katzhendler

Schneider

Ta‐Shma

et al. 2000

J. Chem. Soc., Perkin Trans. 2

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The thermodynamics, pH dependency and solvent effects of the fragmentation reaction of a series of α-oxyiminobenzylphosphonate monomethyl esters [(E)-1a-f ] were examined in water and other hydroxylic solvents by UV and by 31 P NMR spectroscopy at pH 0-3.1. The fragmentation of compounds (E)-1a-f was found to be a first-order reaction in substrate over the acidity range studied, while the dependence on the acidity is more complex, with rate constants k 1 and k 2 . The ρ values corresponding to the first and second order rate constants were Ϫ1.12 and Ϫ0.835, respectively, indicating that the reaction is facilitated by electron-donating substituents, which probably enhance the protonation of the oxime OH group. Activation parameters for k 1 and k 2 reactions were also calculated. The nearzero values of the entropies of activation obtained are consistent with a dissociative transition state with almost no bonding to a nucleophilic solvent. Monitoring the fragmentation reaction of (E)-1a in several binary alcohol-water mixtures at different acidities showed that the reaction rate is enhanced by the alcohol's acidity and not hampered by the steric requirements of the alcohol molecule. This rules out in our opinion, the likelihood for nucleophilic solvent assistance in the rate-determining step. On the other hand, product studies show that both the nucleophilicity and the steric requirements of the alcohol are of importance in determining the product formed in the fragmentation of (E)-1a. The highest selectivity (S) value was found for MeOH, while S values of <1 were observed for 2,2,2trifluoroethanol and the sterically hindered alcohols. The divergence between the effects of the solvent on the rate, on the one hand, and on the products on the other, indicates that the rate limiting step and the product determining step do not share a common transition state and that the reaction coordinate includes at least one reactive intermediate, probably methyl metaphosphate. The results are compatible with a dissociative mechanism (D N *A N or D N ϩ A N ), in which the solvating water molecules pull the departing water molecule into the hydration shell, while the solvated phosphonic group becomes a metaphosphate without nucleophilic assistance. The fragmentation of oxyiminobenzylphosphonates to metaphosphate is perceived as a special case of the "abnormal" Beckmann reaction.

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Stereoselectivity in fragmentation and rearrangement of α-hydroxyimino-phosphinates and -phosphonates. A synthetic approach to acylphosphon- and phosphor-amidates. Crystal structures of methyl (E)-α-hydroxyimino-benzylphenylphosphinate and methyl benzoylphenylphosphonamidate

Cited by 25 publications

References 10 publications

Spontaneous Lossen Rearrangement of (Phosphonoformyl)hydroxamates. The Migratory Aptitude of the Phosphonyl Group

Spontaneous Lossen Rearrangement of (Phosphonoformyl)hydroxamates. The Migratory Aptitude of the Phosphonyl Group

Coordination properties of novel hemilabile acetamide-derived P,O phosphine ligands. Crystal structures of Ph2PNHC(O)Me and [PdMe{PPh2NHC(O)Me}{PPh2NHC(O)Me}][O3SCF3] †

Fragmentation of methyl hydrogen α-hydroxyiminobenzylphosphonates — kinetics, mechanism and the question of metaphosphate formation †

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