Are there concentration effects in enantioselective deprotonation of cyclic ketones?

Majewski, Marek; Wu, Fan

doi:10.1016/s0040-4020(02)00363-0

Cited by 14 publications

(4 citation statements)

References 76 publications

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“…Thus, any bias provided by the chiral amides that favors one helical conformation over the other could play a determining role in the observed selectivity. This explanation differs significantly over the usual rationalizations in that it emphasizes the interactions within the reagent rather than direct interactions between the amide groups of the reagent and the substrate 5 Possible Conformations of 4-Substituted Cyclohexanones Coordinated to a Magnesium Bis(amide) …”

Section: Discussionmentioning

confidence: 97%

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Kinetics and Mechanism of Ketone Enolization Mediated by Magnesium Bis(hexamethyldisilazide)

Morris

Noll

et al. 2006

J. Am. Chem. Soc.

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Magnesium bis(hexamethyldisilazide), Mg(HMDS)(2), reacts with substoichiometric amounts of propiophenone in toluene solution at ambient temperature to form a 74:26 mixture of the enolates (E)- and (Z)-[(HMDS)(2)Mg(2)(mu-HMDS){mu-OC(Ph)=CHCH(3)}], (E)-1 and (Z)-1, which contain a pair of three-coordinate metal centers bridged by an amide and an enolate group. The compositions of (E)-1 and (Z)-1 were confirmed by solution NMR studies and also by crystallographic characterization in the solid state. Rate studies using UV-vis spectroscopy reveal the rapid and complete formation of a reaction intermediate, 2, between the ketone and magnesium, which undergoes first-order decay with rate constants independent of the concentration of excess Mg(HMDS)(2) (DeltaH++ = 17.2 +/- 0.8 kcal/mol, DeltaS++ = -11 +/- 3 cal/mol.K). The intermediate 2 has been characterized by low-temperature (1)H NMR, diffusion-ordered NMR, and IR spectroscopy and investigated by computational studies, all of which are consistent with the formulation of 2 as a three-coordinate monomer, (HMDS)(2)Mg{eta(1)-O=C(Ph)CH(2)CH(3)}. Further support for this structure is provided by the synthesis and structural characterization of two model ketone complexes, (HMDS)(2)Mg(eta(1)-O=C(t)Bu(2)) (3) and (HMDS)(2)Mg{eta(1)-O=C((t)Bu)Ph} (4). A large primary deuterium isotope effect (k(H)/k(D) = 18.9 at 295 K) indicates that proton transfer is the rate-limiting step of the reaction. The isotope effect displays a strong temperature dependence, indicative of tunneling. In combination, these data support the mechanism of enolization proceeding through the single intermediate 2 via intramolecular proton transfer from the alpha carbon of the bound ketone to the nitrogen of a bound hexamethyldisilazide.

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Section: Discussionmentioning

confidence: 97%

“…This explanation differs significantly over the usual rationalizations in that it emphasizes the interactions within the reagent rather than direct interactions between the amide groups of the reagent and the substrate. 66…”

Section: Discussionmentioning

confidence: 99%

Kinetics and Mechanism of Ketone Enolization Mediated by Magnesium Bis(hexamethyldisilazide)

Morris

Noll

et al. 2006

J. Am. Chem. Soc.

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“…Since the time the enantioselective deprotonation of cyclic ketones by a chiral lithium amide was first demonstrated in 1986, 10a 10b the method has been widely utilized in asymmetric synthesis for generating chirality centers in cyclic ketones by desymmetrization. 11 Although efficient desymmetrizations of a number of oxa-, aza-, and thia-heterocyclic ketones by chiral lithium amides have been already demonstrated, 10f 10 12 the corresponding P-heterocyclic analogs have not been investigated before. Thus, we started with checking the viability of enantioselective deprotonations of 1-phenylphosphinan-4-one 1-oxide ( 1a ), 1-borane ( 1b ), and 1-sulfide ( 1c ) using lithium amide derived from amine ( S , S )- 5 as the model base premixed with an excess of TMSCl before addition of a ketone (ISQ - in situ quench) 13 ( Table 1 ).…”

Section: Resultsmentioning

confidence: 99%

Desymmetrization Approach to the Synthesis of Optically Active P-Stereogenic Phosphin-2-en-4-ones

2021

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Two synthetic protocols for the conversion of 1-phenylphosphinan-4-ones to novel P-stereogenic 1-phenylphosphin-2-en-4-ones by enantioselective deprotonation followed by oxidation and by asymmetric organocatalytic halogenation accompanied by elimination have been developed. These two-step one-pot transformations provide convenient access to optically active 1-phenylphosphin-2-en-4-one 1-sulfide and 1-phenylphosphin-2-en-4-one 1-oxide of 96 and 55% enantiomeric purities, respectively.

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“…The mass spectra were recorded at 70eV using HPLC-LCQ Fleet/Thermo Scientific mass spectrophotometer General procedure for the preparation of imines (2a-2h) [7][8][9] Preparation of mono-imines (2a-2d).…”

Section: Experimental Partmentioning

confidence: 99%

Synthesis and Characterization of Some 4-Substituted Thiazolidinone Derivatives

Jebur¹,

Magtoof²

2017

ECB

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Are there concentration effects in enantioselective deprotonation of cyclic ketones?

Cited by 14 publications

References 76 publications

Kinetics and Mechanism of Ketone Enolization Mediated by Magnesium Bis(hexamethyldisilazide)

Kinetics and Mechanism of Ketone Enolization Mediated by Magnesium Bis(hexamethyldisilazide)

Desymmetrization Approach to the Synthesis of Optically Active P-Stereogenic Phosphin-2-en-4-ones

Synthesis and Characterization of Some 4-Substituted Thiazolidinone Derivatives

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