615-13-4Relevant articles and documents
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Johnson et al.
, p. 3793,3795,3796 (1974)
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2-Indanone and Its Enol. The Effect of a Conjugated Phenyl Group on Enol and Enolate Stability
Keeffe, J.R.,Kresge, A.J.,Yin, Y.
, p. 8201 - 8206 (1988)
Rate and equilibrium constants for the interconversion of 2-indanone with its enol and enolate ion have been determined in dilute aqueous acid and base solution (ionic strength=0.10 M) at 25 deg C.These measurements provide the keto-enol equilibrium constant, pKE=3.84+-0.04; the acidity constant of the ketone ionizing as a carbon acid, pKaK=12.20+-0.08; and the acidity constant of the enol ionizing as an oxygen acid, pKaE=8.36+-0.09.Comparison of these results with values for acetone show that the effects of the benzene ring are large: a factor of 1E4.4 on KE, 1E7.0 on KaK, and 1E2.6 on KaE.Considerably smaller phenyl effects are estimated for the acyclic model ketone phenylacetone; reduced coplanarity in the latter is suggested as the major reason for the reduced effects.In terms of rate constants,the greater enol content of 2-indanone relative to acetone manifests itself in the acid-catalyzed reaction mainly as a largely reduced rate of enol ketonization and in the "uncatalyzed" reaction entirely by an increased rate of enolization.For hydroxide ion promoted enolate formation the phenyl effect appears roughly equally as an increase in the rate of enolate formation and a decrease in ketonization rate.It is suggested that the effects of a conjugated benzene ring on enol and enolate stability are fully expressed by the reactions of 2-indanone.
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Askam,Deeks
, p. 2245 (1970)
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Bidentate Nitrogen-Ligated I(V) Reagents, Bi(N)-HVIs: Preparation, Stability, Structure, and Reactivity
Xiao, Xiao,Roth, Jessica M.,Greenwood, Nathaniel S.,Velopolcek, Maria K.,Aguirre, Jordan,Jalali, Mona,Ariafard, Alireza,Wengryniuk, Sarah E.
, p. 6566 - 6576 (2021/05/06)
Hypervalent iodine(V) reagents are a powerful class of organic oxidants. While the use of I(V) compounds Dess-Martin periodinane and IBX is widespread, this reagent class has long been plagued by issues of solubility and stability. Extensive effort has been made for derivatizing these scaffolds to modulate reactivity and physical properties but considerable room for innovation still exists. Herein, we describe the preparation, thermal stability, optimized geometries, and synthetic utility of an emerging class of I(V) reagents, Bi(N)-HVIs, possessing datively bound bidentate nitrogen ligands on the iodine center. Bi(N)-HVIs display favorable safety profiles, improved solubility, and comparable to superior oxidative reactivity relative to common I(V) reagents. The highly modular synthesis and in situ generation of Bi(N)-HVIs provides a novel and convenient screening platform for I(V) reagent and reaction development.
Cycloaddition of carbon dioxide to epoxides by highly active constrained aluminum chloride complexes
Laiwattanapaisarn, Nattiya,Phomphrai, Khamphee,Virachotikul, Arnut
, p. 11039 - 11048 (2021/08/24)
The transformation of carbon dioxide (CO2) and epoxides to cyclic carbonates has gained much interest due to its low cost, abundance, low toxicity, and renewability. Therefore, novel constrained aluminum chloride complexes were developed based on bis(salicylimine) ligands for epoxides/CO2 coupling reactions. The five-membered rings attached to the aromatic rings were designed to enlarge the coordination pocket around the aluminum center as demonstrated by single-crystal X-ray crystallography. Addition of propylene oxide (PO) to a mixture of an aluminum chloride complex and tetrabutylammonium bromide (TBAB) rapidly gave (ligand)Al-OCH(Me)CH2Cl and (ligand)Al-OCH(Me)CH2Br in similar quantities. The anion exchange between (ligand)Al-Cl and TBAB was found to be faster than the ring-opening of PO. From a series of catalyst screening and optimization, the combination of catalyst 2g having no substituent on the aromatic rings and TBAB displayed very high activity (TOF up to 10?800 h-1) for the PO/CO2 coupling reaction. This catalyst system was extended to eleven more examples of epoxides. Moreover, excellent selectivity for cyclic carbonate production was observed for both terminal and internal epoxides.
Asymmetric azidohydroxylation of styrene derivatives mediated by a biomimetic styrene monooxygenase enzymatic cascade
Franssen, Maurice C. R.,Hollmann, Frank,Martínez-Montero, Lía,Paul, Caroline E.,Süss, Philipp,Schallmey, Anett,Tischler, Dirk
, p. 5077 - 5085 (2021/08/16)
Enantioenriched azido alcohols are precursors for valuable chiral aziridines and 1,2-amino alcohols, however their chiral substituted analogues are difficult to access. We established a cascade for the asymmetric azidohydroxylation of styrene derivatives leading to chiral substituted 1,2-azido alcohols via enzymatic asymmetric epoxidation, followed by regioselective azidolysis, affording the azido alcohols with up to two contiguous stereogenic centers. A newly isolated two-component flavoprotein styrene monooxygenase StyA proved to be highly selective for epoxidation with a nicotinamide coenzyme biomimetic as a practical reductant. Coupled with azide as a nucleophile for regioselective ring opening, this chemo-enzymatic cascade produced highly enantioenriched aromatic α-azido alcohols with up to >99% conversion. A bi-enzymatic counterpart with halohydrin dehalogenase-catalyzed azidolysis afforded the alternative β-azido alcohol isomers with up to 94% diastereomeric excess. We anticipate our biocatalytic cascade to be a starting point for more practical production of these chiral compounds with two-component flavoprotein monooxygenases.
