Hydride‐Donor Abilities of 1,4‐Dihydropyridines: A Comparison with π Nucleophiles and Borohydride Anions

Richter, Dorothea; Mayr, Herbert

doi:10.1002/anie.200804263

Cited by 87 publications

(44 citation statements)

References 54 publications

(22 reference statements)

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“…The published data18, 19, 22–34, 40 using Eqn (4) provide a different viewpoint, based on electrophilicities; substituent effects on the reactivities of benzhydrylium ions are obtained more directly and precisely, using a nucleophile‐specific (substituent effect) s parameter. The subsequent, indirect evaluation of N from Eqn (4) requires long extrapolations, and could be improved by moving the standard electrophile to lower values of E .…”

Section: Discussionmentioning

confidence: 99%

“…The subsequent, indirect evaluation of N from Eqn (4) requires long extrapolations, and could be improved by moving the standard electrophile to lower values of E . However, the attractive plots18, 19, 22–34, 40 of data for overlapping reaction series of benzhydrylium ions are not suitable for analysis using the ‘overlap assumption’,17 because the slopes ( s ) using Eqn (4) vary (e.g. Table 7) and so the plots are not parallel.…”

Section: Discussionmentioning

confidence: 99%

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A design to prevent floating within the N scale of nucleophilicity

Bentley¹

2010

J of Physical Organic Chem

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Two nucleophilicity scales (N′ and N″) including 96 nucleophiles, spanning 1017 in rate constant, have been constructed directly from experimental rate constants for reactions of nucleophiles with dianisyl (log k = N′) or dimethylaminobenzhydrylium (log k = N″) cations in dichloromethane at 20 °C. The two scales are linked/unified by the formula: N′ − N″ = 6.6. In contrast, published procedures (H. Mayr et al. J. Am. Chem. Soc. 2001, 123, 9500, and later work) involve 23 benzhydrylium cations and over 200 adjustable parameters obtained from the equation log k = s(E + N), where k is the rate constant, E is an electrophilicity parameter and s is a nucleophile‐specific sensitivity parameter. The definitions of N′ and N″ avoid a floating N scale, i.e. having less than the usual attachment to fixed reference points. New equations, log k = (E + sN′) or log k = (E + sN″), where s is now an electrophile‐specific parameter, are then used to correlate over 350 second‐order rate constants for reactions of other benzhydrylium cations with nucleophiles. For weaker, less polar, nucleophiles, s ∼ 1 and the new E and N′ parameters are in satisfactory agreement with published data for E and N. For more polar nucleophiles, s ≠ 1 and values of N − N″ vary by five log units. Copyright © 2010 John Wiley & Sons, Ltd.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

A design to prevent floating within the N scale of nucleophilicity

Bentley¹

2010

J of Physical Organic Chem

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“…By this measure, NHC-boranes are among the best neutral hydride donors known, more reactive than distant relatives such as silanes, stannanes, and dihydropyridines, and more reactive even than their amine-borane cousins [15–19]. Despite being neutral, 1,3-dimethylimidazol-2-ylidene borane (diMe-Imd-BH 3 , 1 , see Scheme 1) has an N value ( N = 12) that is roughly comparable to the anion cyanoborohydride (NaBH 3 CN) in DMSO.…”

Section: Introductionmentioning

confidence: 99%

Reductions of aldehydes and ketones with a readily available N-heterocyclic carbene borane and acetic acid

Lamm¹,

Pan²,

Taniguchi³

et al. 2013

Beilstein J. Org. Chem.

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SummaryAcetic acid promotes the reduction of aldehydes and ketones by the readily available N-heterocyclic carbene borane, 1,3-dimethylimidazol-2-ylidene borane. Aldehydes are reduced over 1–24 h at room temperature with 1 equiv of acetic acid and 0.5 equiv of the NHC-borane. Ketone reductions are slower but can be accelerated by using 5 equiv of acetic acid. Aldehydes can be selectively reduced in the presence of ketones. On a small scale, products are isolated by evaporation of the reaction mixture and direct chromatography.

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“…It has been shown, however, that the same E parameters of tritylium ions that were derived from their reactions with n-nucleophiles could also be used for hydride transfer reactions [26,29,58]. Kinetic data that were obtained by the benzhydrylium method could, therefore, be supplemented by literature data for hydride transfer reactions towards tritylium ions.…”

Section: Discussionmentioning

confidence: 96%

“…By using the benzhydrylium method, it was possible to determine the nucleophilicity parameter N (and s N ) of various classes of hydride donors, including hydrocarbons, silanes, stannanes, borohydrides and dihydropyridines [19,[55][56][57][58][59].…”

Section: Reactions Of Hydride Donors With Benzhydrylium and Trityliummentioning

confidence: 99%

Benzhydrylium and tritylium ions: complementary probes for examining ambident nucleophiles

Ofial

2015

Pure and Applied Chemistry

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The linear free energy relationship log k = s N (N + E) (eq. 1), in which E is an electrophilicity, N is a nucleophilicity, and s N is a nucleophile-dependent sensitivity parameter, is a reliable tool for predicting rate constants of bimolecular electrophile-nucleophile combinations. Nucleophilicity scales that are based on eq. (1) rely on a set of structurally similar benzhydrylium ions (Ar 2 CH + ) as reference electrophiles. As steric effects are not explicitely considered, eq. (1) cannot unrestrictedly be employed for reactions of bulky substrates. Since, on the other hand, the reactions of tritylium ions (Ar 3 C + ) with hydride donors, alcohols, and amines were found to follow eq. (1), tritylium ions turned out to be complementary tools for probing organic reactivity. Kinetics of the reactions of Ar 3 C + with π-nucleophiles (olefins), n-nucleophiles (amines, alcohols, water), hydride donors and ambident nucleophiles, such as the anions of 5-substituted Meldrum's acids, are discussed to analyze the applicability of tritylium ions as reference electrophiles.

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Hydride‐Donor Abilities of 1,4‐Dihydropyridines: A Comparison with π Nucleophiles and Borohydride Anions

Cited by 87 publications

References 54 publications

A design to prevent floating within the N scale of nucleophilicity

A design to prevent floating within the N scale of nucleophilicity

Reductions of aldehydes and ketones with a readily available N-heterocyclic carbene borane and acetic acid

Benzhydrylium and tritylium ions: complementary probes for examining ambident nucleophiles

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