- Metal-Free 2,2,6,6-tetramethylpiperidin-1-yloxy radical (TEMPO) catalyzed aerobic oxidation of hydroxylamines and alkoxyamines to oximes and oxime ethers
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TEMPO-Mediated oxidation of hydroxylamines (=hydroxyamines) and alkoxyamines to the corresponding oxime derivatives is reported (TEMPO=2,2,6,6-tetramethylpiperidin-1-yloxy radical; Scheme 2). These environmentally benign oxidations proceed in good to excellent yields (Table 1). For alkoxyamines, oxidation to the corresponding oxime ethers can be performed by using dioxygen as a terminal oxidant in the presence of 5-10 mol-% of TEMPO or 4-substituted derivatives thereof as a catalyst (Scheme 3 and Table 2). Importantly, benzyl bromides can directly be transformed to oxime ethers via in situ alkoxyamine formation by a nucleophilic substitution followed by TEMPO-mediated oxidation (Scheme 4 and Table 3). Copyright
- Wertz, Sebastian,Studer, Armido
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p. 1758 - 1772,15
(2012/12/13)
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- CATALYTIC ASYMMETRIC SYNTHESIS OF PRIMARY AMINES VIA BORANE REDUCTION OF OXIME ETHERS USING SPIROBORATE ESTERS
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Asymmetric reduction of arylalkyl and pyridylalkyl ketoxime ether with borane catalyzed by several chiral spiroborates derived from non-racemic 1,2-amino alcohols are presented. Complete conversion of oxime to primary amine is highly dependant of the catalyst, source and amount of borane and temperature. The conversion and enantioselectivity is determined by the benzylic substitution of the oxime. After optimization, a catalyst derived from diphenyl valinol could, successfully, afford primary amines with good yield and enantioselectivity up to 99% ee. Using the developed methodology, other related non-racemic primary pyridyl alkyl methanamines were also prepared in high chemical yield and excellent enantioselectivity.
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Page/Page column 18
(2008/06/13)
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- Asymmetric synthesis of primary amines via the spiroborate-catalyzed borane reduction of oxime ethers
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The enantioselective borane reduction of O-benzyloxime ethers to primary amines was studied under catalytic conditions using the spiroborate esters 5-10 derived from nonracemic 1,2-amino alcohols and ethylene glycol. Effective catalytic conditions were achieved using only 10% of catalyst 5 derived from diphenylvalinol in dioxane at 0°C resulting in complete conversion to the corresponding primary amine in up to 99% ee.
- Huang, Xiaogen,Ortiz-Marciales, Margarita,Huang, Kun,Stepanenko, Viatcheslav,Merced, Francisco G.,Ayala, Angel M.,Correa, Wildeliz,De Jesus, Melvin
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p. 1793 - 1795
(2008/02/02)
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- Asymmetric reduction of oxime ethers promoted by chiral spiroborate esters with an O3BN framework
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Enatioselective reduction of oxime ethers promoted by chiral spiroborate esters with an O3BN framework is reported for the first time. In the presence of (R,S)-1, 11 aralkyloxime ethers are reduced by borane-THF at 0-5 °C to give (S)-1-aralkylamine in high yield and excellent enatiomeric excess (up to 98% ee). Influence of reaction conditions on the enantioselectivity of the reduction is investigated, and a possible mechanism of the catalytic reduction is suggested.
- Chu, Yunbo,Shan, Zixing,Liu, Dejun,Sun, Nannan
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p. 3998 - 4001
(2007/10/03)
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