- Enantioenriched ω-bromocyanohydrin derivatives. Improved selectivity by combination of two chiral catalysts
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Highly enantioenriched (R)-4-bromo-1-cyanobutyl acetate and (R)-5-bromo-1-cyanopentyl acetate were prepared by acetylcyanation of 4-bromobutanal and 5-bromopentanal, respectively, catalyzed by (S,S)-[(4,6-bis(t-butyl)salen)Ti(μ-O)]2 and triethylamine followed by enzymatic hydrolysis of the minor enantiomer. A cyclic procedure employing the same two chiral catalysts provided inferior results due to a slowly reached steady state and, in reactions with the former substrate, to ring-closure of the free cyanohydrin formed as an intermediate in the reaction. Hydrolysis of the acylated cyanohydrins followed by AgClO4-promoted cyclization provided (R)-2-cyanotetrahydrofuran and (R)-2-cyanotetrahydropyran in essentially enantiopure form.
- Hertzberg, Robin,Widyan, Khalid,Heid, Berenice,Moberg, Christina
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p. 7680 - 7684
(2012/09/08)
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- Method of preparing optically pure (R) - or (S) - tetrahydrofuranyl ketone
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Disclosed is a method of preparing an optically pure (R)- or (S)-tetrahydrofuranyl ketone. By such a method, (R)- or (S)-2-tetrahydrofuran amide is converted to (R)- or (S)-2-tetrahydrofuran nitrile through dehydration in the presence of a dehydrating agent and an amine base. Then, thus prepared (R)- or (S)-2-tetrahydrofuran nitrile is nucelophilic addition-reacted with a nucleophile, followed by hydrolyzing, thereby produce (R)- or (S)-tetrahydrofuranyl ketone having high optical purity, while minimizing production of other by-products.
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- Method of preparing optically pure (R)- or (S)- tetrahydrofuranyl ketone
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Disclosed is a method of preparing an optically pure (R)-or (S)-tetrahydrofuranyl ketone. By such a method, (R)-or (S)-2-tetrahydrofuran amide is converted to (R)- or (S)-2-tetrahydrofuran nitrile through dehydration in the presence of a dehydrating agent and an amine base. Then, thus prepared (R)- or (S)-2-tetrahydrofuran nitrile is nucelophilic addition-reacted with a nucleophile, followed by hydrolyzing, thereby produce (R)- or (S)-tetrahydrofuranyl ketone having high optical purity, while minimizing production of other by-products.
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- Optically Active (S)-Ketone- and (R)-Aldehyde-cyanohydrins via an (R)-Oxynitrilase-catalysed Transcyanation. Chemoenzymatic Syntheses of 2-Cyanotetrahydrofuran and 2-Cyanotetrahydropyran
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(R)-Oxynitrilase catalyses the enantioselective decyanation of racemic ketone cyanohydrins and the enantioselective addition of HCN to ω-bromoaldehydes in one step.
- Menendez, Emma,Brieva, Rosario,Rebolledo, Francisca,Gotor, Vicente
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p. 989 - 990
(2007/10/02)
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