- Enantioselective reduction of ketoxime ethers with borane-oxazaborolidines and synthesis of the key intermediate leading to (S)-rivastigmine
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The reduction of representative alkyl aryl (E)-ketoxime O-benzyl ethers with borane catalyzed by terpene oxazaborolidines, derived from (1R)-nopinone and (1R)-camphor, gave the corresponding amines with 82-99% ee. Oxazaborolidines derived from (1S)-2-carene and (1S)-3-carene were less selective. (S)-1-(3-Methoxyphenyl)ethanamine (94% ee) the key intermediate in the synthesis of (S)-rivastigmine, was obtained by the reduction of (E)-1-(3-methoxyphenyl) ethanone O-benzyl oxime with borane/oxazaborolidine generated from (S)-valinol.
- Pakulski, Marcin M.,Mahato, Sanjit K.,Bosiak, Mariusz J.,Krzeminski, Marek P.,Zaidlewicz, Marek
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p. 716 - 721
(2012/09/21)
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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 18-20
(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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