- Dynamic kinetic resolution of 2-methyl-2-nitrocyclohexanol: Combining the intramolecular nitroaldol (Henry) reaction & lipase-catalysed resolution
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Efforts to combine the intramolecular nitroaldol reaction with lipase-catalysed resolution of the resulting nitroaldol adduct in a one-pot dynamic kinetic resolution (DKR) are described. Significant challenges were encountered in the combination of the two systems. trans-2-Methyl-2-nitrocyclohexyl acetate (±)-3b was isolated in excellent enantiopurity (>98% ee) via a sequential DKR sequence where the lipase-mediated resolution and base-mediated interconversion of 2-methyl-2-nitrocyclohexanol 2 were effected alternately, demonstrating the feasibility of this approach initially. Further work showed, for the first time, evidence that a DKR-type system is possible for 2. Reaction engineering allowed the design of a sequential one-pot reaction system which furnished the products with excellent enantioselectivity, and good diastereoselectivity.
- Foley, Aoife M.,Gavin, Declan P.,Deasy, Rebecca E.,Milner, Sinéad E.,Moody, Thomas S.,Eccles, Kevin S.,Lawrence, Simon E.,Maguire, Anita R.
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p. 1435 - 1443
(2018/02/23)
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- Copper-Assisted Direct Nitration of Cyclic Ketones with Ceric Ammonium Nitrate for the Synthesis of Tertiary α-Nitro-α-substituted Scaffolds
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An efficient and direct Cu-assisted nitrating approach to create synthetically valuable and challenging tertiary α-nitro-α-substituted moieties has been developed using ceric ammonium nitrate as a nitrating reagent, oxidant, and Lewis acid. Notably, the commonly used clinical drug ketamine was smoothly synthesized in four steps.
- Zhang, Zhi-Qiang,Chen, Tao,Zhang, Fu-Min
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supporting information
p. 1124 - 1127
(2017/03/15)
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- α-nitration of ketones via enol silyl ethers. Radical cations as reactive intermediates in thermal and photochemical processes
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Highly colored (red) solutions of various enol silyl ethers and tetranitromethane (TNM) are readily bleached to afford good yields of α-nitro ketones in the dark at room temperature or below. Spectral analysis show the red colors to be associated with the intermolecular 1:1 electron donor-acceptor (EDA) complexes between the enol silyl ether and TNM. The formation of similar vividly colored EDA complexes with other electron acceptors (such as chloranil, tetracyanobenzene, tetracyanoquinodimethane, etc.) readily establish enol silyl ethers to be excellent electron donors. The deliberate irradiation of the diagnostic (red) charge-transfer absorption bands of the EDA complexes of enol silyl ethers and TNM at -40 °C affords directly the same α-nitro ketones, under conditions in which the thermal reaction is too slow to compete. A common pathway is discussed in which the electron transfer from the enol silyl ether (ESE) to TNM results in the radical ion triad [ESE?+, NO2?, C(NO2)3-]. A subsequent fast homolytic coupling of the cation radical of the enol silyl ether with NO2? leads to the α-nitro ketones. The use of time-resolved spectroscopy and the disparate behavior of theisomeric enol silyl ethers of α- and β-tetralones as well as of 2-methylcyclohexanone strongly support cation radicals (ESE?+) as the critical intermediate in thermal and photoinduced electron-transfer as described in Schemes 1 and 2, respectively.
- Rathore, Rajendra,Kochi, Jay K.
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p. 627 - 639
(2007/10/03)
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- Facile Preparation of α-Nitroketones from Enol Silyl Ethers
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Treatment of enol silyl ethers with the mild nitrating agent tetranitromethane gives good yields of α-nitroketones at room temperature and below.
- Rathore, Rajendra,Lin, Zhe,Kochi, Jay K.
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p. 1859 - 1862
(2007/10/02)
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- α-Nitro Ketones. 6. Synthesis and Conformation of 2-Methyl-2-nitro-, cis- and trans-6-Methyl-2-nitro-, and cis- and trans-2,6-Dimethyl-2-nitrocyclohexanones
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Nitration of the most substituted (thermodynamically more stable) enol acetate or trimethylsilyl ether of 2-methylcyclohexanone and the phase-transfer methylation of 2-nitrocyclohexanone serve as methods of preparation of 2-methyl-2-nitrocyclohexanone, whereas nitration of the least substituted enol acetate or trimethylsilyl ether of 2-methylcyclohexanone and methylation of the dianion of 2-nitrocyclohexanone lead to cis- and trans-6-methyl-2-nitrocyclohexanone.Nitration of the enol acetate or trimethylsilyl ether of 2,6-dimethylcyclohexanone and methylation of either2-methyl-2-nitro- or 6-methyl-2-nitrocyclohexanone are methods of preparation of cis- and trans-2,6-dimethyl-2-nitrocyclohexanone. 1H NMR chemical shift and coupling constant data were used to determine the preferred conformations of the cyclohexanones: 2(e)-methyl-2(a)-nitro, cis-6(e)-methyl-2(e)-nitro, trans-6(e)-methyl-2(a)-nitro, cis-2(e),6(e)-dimethyl-2(a)-nitro, trans-2(a)-methyl-6(e)-methyl-2(e)-nitro.
- Dampawan, Pimchit,Zajac, Walter W.
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p. 1176 - 1181
(2007/10/02)
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