Carbon acids. 12. Acidifying effects of phenyl substituents

Bordwell, F. G.; Bares, Joseph E.; Bartmess, John E.; McCollum, Gregory J.; Puy, Michael Van Der; Vanier, Noel R.; Matthews, Walter S.

doi:10.1021/jo00422a032

Cited by 79 publications

(45 citation statements)

References 5 publications

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“…A similar effect is observed for phenyl substitution into acetophenone (a 6.8 increase) (6). Extensive delocalization of the negative charge in the anion (R effect), as illustrated in 36, is responsible for these changes.…”

Section: Resultsmentioning

confidence: 55%

Acidities and homolytic bond dissociation energies of the αC—H bonds in ketones in DMSO

Bordwell¹,

Harrelson²

1990

Can. J. Chem.

118

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Can. J. Chem. 68, 1714 (1990). Equilibrium acidities in DMSO are reported for nine cycloalkanones, acetone, acetophenone, and 19 of their a-substituted derivatives. Oxidation potentials in DMSO for the conjugate bases of most of these ketones are also reported. Combination of these Eox(A-) and pKHA values gives estimates of the homolytic bond dissociation energies (BDEs) of the acidic C-H bonds in the ketones. The ABDEs, relative to the BDE of CH3-H, or a parent ketone, provide a measure of the radical stabilization energies (RSEs) of the corresponding radicals. The effects of successive a-Me and a-Ph substitutions on RSEs, relative to those of CH3COCH2-H or PhCOCH2-H, are similar to those reported in the gas phase for methane. The RSE for the MeCHCOPh radical, relative to CH3* is 17 kcal/mol, which is smaller than the sum of the RSEs of the MeCH2* and PhCOCH2* radicals relative to CH3* (7 + 12 = 19), contrary to the prediction of the captodative postulate. When G in PhCOCH2G is PhCO, CH3C0, or CN the ABDEs (relative to PhCOCH2-H) are 0, 1, and 3 respectively; for MeCOCH2S02Ph, PhCOCH2S02Ph, and P~C O C H~N M~~' the ABDEs are -5, -2, and -4, respectively. The BDEs in C5, C6, C7. C8, ClO, and C12cycloalkanones are within k2.5 kcal/mol of that of 3-pentanone. Acetophenones bearing meta or para substituents all have BDEs of 93-94 kcal/mol. Ketone radical cations, [RCOR']", appear to be superacids with estimated pKHA+* values below -25.

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Section: Resultsmentioning

confidence: 55%

Acidities and homolytic bond dissociation energies of the αC—H bonds in ketones in DMSO

Bordwell¹,

Harrelson²

1990

Can. J. Chem.

118

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“…Regarding the mechanism of the aza-Henry reaction, the observed high stereocontrol can be rationalized by a bifunctional mode of action in which the iridium catalyst-after the initial proton transfer between catalyst and nitro substrate (pK a B12 in dimethylsulphoxide) 60 -controls a ternary complex with the intermediate nitronate anion and the N-Boc-Schiff base through defined hydrogen bonds as displayed in Fig. 4a.…”

Section: Discussionmentioning

confidence: 99%

Metal-templated chiral Brønsted base organocatalysis

Ding

et al. 2014

Nat Commun

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Inert octahedral chiral-at-metal complexes are an emerging class of asymmetric catalysts that exploit the globular, rigid nature and stereochemical options of octahedral compounds. While the central transition metal serves as a structural anchorpoint and provides metal centrochirality, catalysis is mediated through the organic ligand sphere, thereby merging the branches of transition metal catalysis and organocatalysis. Here we report the development of inert octahedral 3-aminopyrazolato iridium(III) complexes as novel chiral Brønsted base catalysts and demonstrate their merit with applications to highly effective asymmetric sulfaMichael and aza-Henry reactions, permitting catalyst loadings down to 0.02 and 0.25 mol%, respectively. The observed high stereocontrol can be rationalized by a bifunctional mode of action in which the iridium catalyst, after the initial proton transfer, controls a ternary complex through defined hydrogen bonding interactions. This work reveals the potential of octahedral metal complexes as chiral scaffolds for the design of high-performance asymmetric catalysts.

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“…This result is consistent with our mechanistic hypothesis, as the pK a of a benzyl nitrile is very similar to that of phenyl acetate, and the putative nucleophilic tautomer is likely as accessible under these reaction conditions. 13 The more acidic benzylmethyl ketone derivative also cleanly undergoes another oxidation cycle, however we have not as yet identified reaction conditions to efficiently convert the corresponding aniline-N-oxide into the corresponding ketoindoline, which may be suggestive of a fine balance of acid/base equilibria at play in this cyclization. We have developed a sequence of reactions for the synthesis of diversely substituted N-methylindolines from simple N,N-dimethylanilines under exceptionally mild reaction conditions.…”

mentioning

confidence: 84%