- Quantitative production of butenes from biomass-derived γ-valerolactone catalysed by hetero-atomic MFI zeolite
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The efficient production of light olefins from renewable biomass is a vital and challenging target to achieve future sustainable chemical processes. Here we report a hetero-atomic MFI-type zeolite (NbAlS-1), over which aqueous solutions of γ-valerolactone (GVL), obtained from biomass-derived carbohydrates, can be quantitatively converted into butenes with a yield of >99% at ambient pressure under continuous flow conditions. NbAlS-1 incorporates simultaneously niobium(v) and aluminium(iii) centres into the framework and thus has a desirable distribution of Lewis and Br?nsted acid sites with optimal strength. Synchrotron X-ray diffraction and absorption spectroscopy show that there is cooperativity between Nb(v) and the Br?nsted acid sites on the confined adsorption of GVL, whereas the catalytic mechanism for the conversion of the confined GVL into butenes is revealed by in situ inelastic neutron scattering, coupled with modelling. This study offers a prospect for the sustainable production of butene as a platform chemical for the manufacture of renewable materials.
- Lin, Longfei,Sheveleva, Alena M.,da Silva, Ivan,Parlett, Christopher M. A.,Tang, Zhimou,Liu, Yueming,Fan, Mengtian,Han, Xue,Carter, Joseph H.,Tuna, Floriana,McInnes, Eric J. L.,Cheng, Yongqiang,Daemen, Luke L.,Rudi?, Svemir,Ramirez-Cuesta, Anibal J.,Tang, Chiu C.,Yang, Sihai
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- Strong and Confined Acids Control Five Stereogenic Centers in Catalytic Asymmetric Diels–Alder Reactions of Cyclohexadienones with Cyclopentadiene
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We describe a highly enantioselective Diels–Alder reaction of cross-conjugated cyclohexadienones with cyclopentadiene, in which five stereocenters are effectively controlled by a strongly acidic and confined imidodiphosphorimidate catalyst. Our approach provides tricyclic products in excellent stereoselectivity. We also report methods to convert the obtained products into useful intermediates and a computational study that aids in gaining deeper insight into the reaction mechanism and origin of stereoselectivity.
- Bistoni, Giovanni,Das, Sayantani,De, Chandra Kanta,Ghosh, Santanu,Leutzsch, Markus,List, Benjamin,Neese, Frank,Yepes, Diana
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supporting information
p. 12347 - 12351
(2020/03/23)
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- Asymmetric Synthesis of Remote Quaternary Centers by Copper-Catalyzed Desymmetrization: An Enantioselective Total Synthesis of (+)-Mesembrine
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Catalytic asymmetric syntheses of remote quaternary stereocenters have been developed by copper-catalyzed 1,4-hydrosilylation of ?,?-disubstituted cyclohexadienones. A variety of cyclohexenones have been synthesized in good yield and excellent enantioselectivity. Versatile 2-silyloxy diene intermediates bearing ?,?-disubstituted all carbon stereogenic centers can be isolated from the mild reaction conditions. The utility of this strategy is exemplified in a catalytic asymmetric total synthesis of (+)-mesembrine.
- Bokka, Apparao,Mao, James X.,Hartung, John,Martinez, Steven R.,Simanis, Justin A.,Nam, Kwangho,Jeon, Junha,Shen, Xiaoqiang
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supporting information
p. 5158 - 5162
(2018/09/13)
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- Asymmetric Baeyer - Villiger oxidations of 4-mono- and 4,4-disubstituted cyclohexanones by whole cells of engineered Escherichia coli
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Whole cells of an Escherichia coli strain that overexpresses Acinetobacter sp. NCIB 9871 cyclohexanone monooxygenase have been used for the Baeyer-Villiger oxidations of a variety of 4-mono- and 4,4-disubstituted cyclohexanones. In cases where comparisons were possible, this new biocatalytic reagent provided lactones with chemical yields and optical purities that were comparable to those obtained from the purified enzyme or a strain of bakers' yeast that expresses the same enzyme. The efficient production of cyclohexanone monooxygenase in the E. coli expression system (ca. 30% of total soluble protein) allowed these oxidations to reach completion in approximately half the time required for the engineered bakers' yeast strain. Surprisingly, 4,4-disubstituted cyclohexanones were also accepted by the enzyme, and the enantioselectivities of these oxidations could be rationalized by considering the conformational energies of bound substrates along with the enzyme's intrinsic enantioselectivity. The enzyme expressed in E. coli cells also oxidized several 4-substituted cyclohexanones bearing polar substituents, often with high enantioselectivities. In the case of 4-iodocyclohexanone, the lactone was obtained in > 98% ee and its absolute configuration was assigned by X-ray crystallography. The crystal belongs to the monoclinic P21 space group with a = 5.7400(10), b = 6.1650(10), c = 11.377(2) A, b = 99.98(2)°, and Z = 2. Taken together, these results demonstrate the utility of an engineered bacterial strain in delivering useful chiral building blocks in an experimentally simple manner.
- Mihovilovic,Chen,Wang,Kyte,Rochon,Kayser,Stewart
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p. 733 - 738
(2007/10/03)
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- Stereospecific Rearrangement of 2,2-Disubstituted Vinylsilane Epoxides to the Silyl Enol Ethers of 2,2-Disubstituted Aldehydes
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The Z- and E-2-ethyl-2-methylvinylsilane epoxides (5a) and (5b) rearrange stereospecifically in the presence of boron trifluoride-diethyl ether to the Z- and E-silyl enol ethers, (6a) and (6b), respectively, of 2-methylbutanal.These silyl enol ethers reac
- Fleming, Ian,Newton, Trevor W.
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p. 119 - 124
(2007/10/02)
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- Anti-androgen compounds
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Compounds of the formula STR1 in which each R is hydrogen, C 1 -C 4 alkyl, C 1 -C 4 alkoxy, hydroxy, cyano, or halo, and both R groups are identical and are symmetrically located; R 1 is C 1 -C 3 alkyl and R 2 is methyl, or R 1 and R 2 taken together are (CH 2 -- n in which n is an integer from 4 to 6; and (1) X c and X d are hydrogen, and the combination of X a and Y a and of X b and Y b each represents a double bond, subject to the limitation that, when R 1 is C 1 -C 3 alkyl and is other than methyl, X c, X d, and R 1 are all in an α-configuration; or (2) X a, X b, X c, X d, Y a, and Y b are hydrogen, subject to the limitation that both X c and X d are in an α-configuration, both X a and X b are in an α-configuration or in a β-configuration, and, R 1, when it is C 1 -C 3 alkyl, is in an α-configuration, are useful in inhibiting the action of androgens or are intermediates to such anti-androgen compounds.
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