Effect of Addends on Aggregation and Reactivity of the Lithium Enolate of <i>p</i>-Phenylisobutyrophenone<sup>1</sup>

Leung, Simon Shun-Wang; Streitwieser, Andrew

doi:10.1021/jo990075p

Cited by 22 publications

(8 citation statements)

References 14 publications

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“…At still higher concentrations when the solvent is 10% HMPA, λ max goes up only slightly more to 470 nm. Because HMPA does tend to break up enolate aggregates to monomers, these results indicate that the observed λ max of 1 -Li is that of an aggregate and that the equilibrium constant for aggregation is too high for detection of monomer.…”

Section: Introductionmentioning

confidence: 93%

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Aggregation and Reactivity of the Dilithium and Dicesium Enediolates of 1-Naphthylacetic Acid¹

2003

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UV-vis spectra of the dilithium, 1-Li, and dicesium, 1-Cs, enediolates of alpha-naphthylacetic acid show no systematic change with concentration in dilute THF solution, but addition of small amounts of HMPA causes a bathochromic shift in the spectrum of 1-Li. These results indicate that these salts are aggregated and that HMPA breaks up the aggregates of 1-Li. The quantitative effect of small increments of HMPA indicates that 1-Li is a dimer. Alkylation reactions of 1-Cs show half-order kinetics in enediolate indicating that this salt is also dimeric but that the small amount of monomer in equilibrium is the actual reactant. Alkylation of 1-Li, however, is much slower and shows first-order kinetics interpreted as a direct reaction of the dimer; the amount of monomer in this case is too small to compete. A solution of 1-Li in THF containing 10% HMPA is much more reactive in alkylation than 1-Li alone and the first-order dependence in 1-Li is now interpreted as reaction of the monomer. Compound 1-Li is found to form a mixed aggregate with LDA, a finding that has possible synthetic significance since enediolates used in syntheses are frequently prepared using LDA. Structures of these compounds are suggested based on model ab initio computations.

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Section: Introductionmentioning

confidence: 93%

“…The HMPA results do provide support that 1 -Li is a dimer. The analysis is based on previous work on the effect of HMPA on the spectrum of a lithium enolate …”

Section: Introductionmentioning

confidence: 99%

Aggregation and Reactivity of the Dilithium and Dicesium Enediolates of 1-Naphthylacetic Acid¹

2003

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“…This effect is also shown by the effects of HMPA, which had been shown earlier to convert lithium enolate aggregates to monomers. 23 This effect of HMPA is wellknown for other lithium compounds, for example, lithium phenolates,, 24 lithiated nitriles, 25 lithium amides, [26][27][28] (but note) 29 lithium chloride, 30 and aryllithiums. [31][32][33] Small amounts of HMPA, up to 0.1 M, have little effect on the λ max of CsPAT, but larger amounts, up to 1 M, cause bathochromic shifts to 385 nm (Figure S11, Supporting Information), the λ max estimated above for the monomer.…”

Section: Spectra and Pk Of Cspatmentioning

confidence: 93%

Section: Alkylation Kineticsmentioning

confidence: 97%

“…In previous work, HMPA was shown to increase rates of reaction with alkylating agents not only by deaggregating enolate aggregates to monomers but also by increasing the reactivity of the monomers. 23 It was shown above that it requires about 1 M HMPA to completely deaggregrate LiPAT to the monomer. Accordingly, the reaction of LiPAT with methyl brosylate in the presence of 0.25 M HMPA is still of fractional order in {LiPAT} but is about 70-fold faster than in the absence of HMPA (Figure S20, Supporting Information).…”

Section: Alkylation Kineticsmentioning

confidence: 98%

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Aggregation and Reactivity of the Cesium Enolate of 6-Phenyl-α-tetralone: Comparison with the Lithium Enolate¹

Wang

Streitwieser

2003

J. Org. Chem.

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The cesium enolate of 6-phenyl-alpha-tetralone (CsPAT) has a lambda(max) in THF at about 387 nm, but the variation with concentration is too small for application of singular value decomposition. Proton-transfer studies with several indicators show that CsPAT forms monomer-tetramer mixtures with a tetramerization equilibrium constant, K(1,4) = 2.3 x 10(11) M(-3). The pK of the monomer is 23.39 on a scale where fluorene is assigned 22.9 (per hydrogen). For comparison, the lithium enolate, LiPAT, is also a monomer-tetramer with K(1,4) = 4.7 x 10(10) M(-3) and a monomer pK = 14.22. HMPA in large amounts promotes dissociation to monomer with both enolates. Ion-pair S(N)2 initial rates were measured for CsPAT with several alkyl halides and with methyl tosylate and compared with other rates with LiPAT. In all cases, the enolate monomers are much more reactive than the aggregates. Reaction of CsPAT with alkyl halides is generally C-alkylation but HMPA promotes increasing amounts of O-alkylation. A new indicator, 11-methyl-11H-benzo[b]fluorene, has a pK on the cesium scale of 23.39.

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N,N′-Dimethylpropyleneurea

Beck

Seebàch

Nikonov³

2012

Encyclopedia of Reagents for Organic Synthesis

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Effect of Addends on Aggregation and Reactivity of the Lithium Enolate of p-Phenylisobutyrophenone¹

Cited by 22 publications

References 14 publications

Aggregation and Reactivity of the Dilithium and Dicesium Enediolates of 1-Naphthylacetic Acid¹

Aggregation and Reactivity of the Dilithium and Dicesium Enediolates of 1-Naphthylacetic Acid¹

Aggregation and Reactivity of the Cesium Enolate of 6-Phenyl-α-tetralone: Comparison with the Lithium Enolate¹

N,N′-Dimethylpropyleneurea

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Effect of Addends on Aggregation and Reactivity of the Lithium Enolate of p-Phenylisobutyrophenone1

Cited by 22 publications

References 14 publications

Aggregation and Reactivity of the Dilithium and Dicesium Enediolates of 1-Naphthylacetic Acid1

Aggregation and Reactivity of the Dilithium and Dicesium Enediolates of 1-Naphthylacetic Acid1

Aggregation and Reactivity of the Cesium Enolate of 6-Phenyl-α-tetralone: Comparison with the Lithium Enolate1

N,N′-Dimethylpropyleneurea

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Effect of Addends on Aggregation and Reactivity of the Lithium Enolate of p-Phenylisobutyrophenone¹

Aggregation and Reactivity of the Dilithium and Dicesium Enediolates of 1-Naphthylacetic Acid¹

Aggregation and Reactivity of the Dilithium and Dicesium Enediolates of 1-Naphthylacetic Acid¹

Aggregation and Reactivity of the Cesium Enolate of 6-Phenyl-α-tetralone: Comparison with the Lithium Enolate¹