- Chemoselective Reduction of Trichloromethyl Compounds to gem-Dichloromethyl Groups Following Appel's Reaction Protocol
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A simple and easy reduction of trichloroacetyl compounds following the modification of Appel's reaction protocol, using triphenylphosphine and methanol, afforded the corresponding dichloroacetyl compounds, with the exception of trichloroacetylmorpholine,
- Romero-Reyes, Moises A.,Zaragoza-Galicia, Ivann,Olivo, Horacio F.,Romero-Ortega, Moises
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- Modular and Chemoselective Strategy for Accessing (Distinct) α,α-Dihaloketones from Weinreb Amides and Dihalomethyllithiums
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The selective transfer of diversely functionalized dihalomethyllithiums (LiCHBrCl, LiCHClI, LiCHBrI, LiCHCl2, LiCHBr2, LiCHFI) to Weinreb amides for preparing gem-dihaloketones in one synthetic operation is reported. The capability of these amides as acylating agents and, the wide availability of dihalomethanes as pronucleophiles, enable a straightforward route to the title compounds under full chemocontrol. No racemization phenomena were evidenced in the case of optically active materials. Additionally, tolerance to sensitive functional groups (esters, amides, halogens, olefins etc.) was uniformly noticed, thus making this conceptually intuitive strategy flexible and tunable by the operator. (Figure presented.).
- Malik, Monika,Pace, Vittorio,Senatore, Raffaele,Touqeer, Saad,Urban, Ernst
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supporting information
p. 5056 - 5061
(2020/10/21)
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- Acid-promoted cleavage of the C–C double bond of N-(2-Hydroxylphenyl)enaminones for the synthesis of benzoxazoles
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An acid-mediated selective cleavage of C–C double bond of N-(2-hydroxylphenyl)enaminones with formation a new C–O bond for the synthesis of 2-substituted benzoxazoles has been developed. This protocol proceeds under transition metal- and oxidant-free conditions with broad functional group tolerance. The oxidative cleavage of C–C double bond of N-(2-hydroxylphenyl)enaminone is also realized using NCS or NFSI as oxidants with release of 2,2-dihalogen-acetophenone fragments.
- Ge, Bailu,Peng, Yanling,Liu, Jing,Wen, Si,Peng, Cheng,Cheng, Guolin
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- Iodine-DMSO-promoted divergent reactivities of arylacetylenes
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An unprecedented set of efficient, economical, atom-economic and exceedingly selective I2-DMSO-promoted methods is described for the generation of different structures. The reaction represents the first of its kind, involving the use of different iodine concentrations, temperatures, acids and salt to adjust the selectivity for the synthesis of different alkenes, α-functionalized ketones and α-ketomethylthioesters.
- Rather, Suhail A.,Kumar, Atul,Ahmed, Qazi Naveed
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supporting information
p. 4511 - 4514
(2019/04/26)
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- Visible-light-promoted oxidative halogenation of alkynes
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In nature, halogenation promotes the biological activity of secondary metabolites, especially geminal dihalogenation. Related natural molecules have been studied for decades. In recent years, their diversified vital activities have been explored for treating various diseases, which call for efficient and divergent synthetic strategies to facilitate drug discovery. Here we report a catalyst-free oxidative halogenation achieved under ambient conditions (halide ion, air, water, visible light, room temperature, and normal pressure). Constitutionally, electron transfer between the oxygen and halide ion is shuttled via simple conjugated molecules, in which phenylacetylene works as both reactant and catalyst. Synthetically, it provides a highly compatible late-stage transformation strategy to build up dihaloacetophenones (DHAPs).
- Li, Yiming,Mou, Tao,Lu, Lingling,Jiang, Xuefeng
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supporting information
p. 14299 - 14302
(2019/12/02)
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- Efficient partial hydrogenation of trichloromethyl to gem-dichloromethyl groups in platinum on carbon-catalyzed system
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While gem-dichloromethyl groups can be directly synthesized by the mono-dechlorination of the corresponding trichloromethyl groups, the suppression control of the over-reduction to form chloromethyl or methyl functionalities is quite difficult. We have established the efficient and widely applicable mono-dechlorination method of the trichloromethyl groups to form the corresponding gem-dichloromethyl groups using platinum on carbon in dimethylacetamide as a specific solvent at 25 °C under a hydrogen atmosphere. The mono-dechlorination of the α,α,α- trichloromethylcarbonyl groups smoothly proceeded by the use of platinum on carbon as a catalyst in a highly chemoselective manner, while the efficient mono-dechlorination of the alkyl- and aryl-trichloromethyl groups required the combined use of Bu3SnH.
- Sawama, Yoshinari,Imanishi, Takahiro,Nakatani, Ryosuke,Fujiwara, Yuta,Monguchi, Yasunari,Sajiki, Hironao
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supporting information
p. 4540 - 4546
(2014/06/10)
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- Expanding the scope of alcohol dehydrogenases towards bulkier substrates: Stereo- and enantiopreference for α,α-dihalogenated ketones
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Alcohol dehydrogenases (ADHs) were identified as suitable enzymes for the reduction of the corresponding α,α-dihalogenated ketones, obtaining optically pure β,β-dichloro- or β,β-dibromohydrins with excellent conversions and enantiomeric excess. Among the different biocatalysts tested, ADHs from Rhodococcus ruber (ADH-A), Ralstonia sp. (RasADH), Lactobacillus brevis (LBADH), and PR2ADH proved to be the most efficient ones in terms of activity and stereoselectivity. In a further study, two racemic α-substituted ketones, namely α-bromo- α-chloro- and α-chloro-α-fluoroacetophenone were investigated to obtain one of the four possible diastereoisomers through a dynamic kinetic process. In the case of the brominated derivative, only the (1R)-enantiomer was obtained by using ADH-A, although with moderate diastereomeric excess (>99 % ee, 63 % de), whereas the fluorinated ketone exhibited a lower stereoselectivity (up to 45 % de). Bulking up: A series of β,β-dihalohydrins are obtained through alcohol dehydrogenase (ADH) catalyzed bioreduction of the synthesized α,α-dihalogenated ketones. Two racemic acetophenone derivatives are also subjected to this protocol to obtain stereoenriched alcohols through dynamic kinetic resolution (DKR).
- Kedziora, Kinga,Bisogno, Fabricio R.,Lavandera, Ivan,Gotor-Fernandez, Vicente,Montejo-Bernardo, Jose,Garcia-Granda, Santiago,Kroutil, Wolfgang,Gotor, Vicente
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p. 1066 - 1072
(2014/05/06)
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- Laccase/TEMPO-mediated system for the thermodynamically disfavored oxidation of 2,2-dihalo-1-phenylethanol derivatives
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An efficient methodology to oxidize β,β-dihalogenated secondary alcohols employing oxygen was achieved in a biphasic medium using the laccase from Trametes versicolor/TEMPO pair, providing the corresponding ketones in a clean fashion under very mild conditions. Moreover, a chemoenzymatic protocol has been applied successfully to deracemize 2,2-dichloro-1-phenylethanol combining this oxidation with an alcohol dehydrogenase-catalyzed bioreduction. the Partner Organisations 2014.
- Kedziora, Kinga,Diaz-Rodriguez, Alba,Lavandera, Ivan,Gotor-Fernandez, Vicente,Gotor, Vicente
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supporting information
p. 2448 - 2453
(2014/05/06)
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- Platinum on carbon-catalyzed precise reduction control of trichloromethyl to Geminal-dichloromethyl groups
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Geminal-dichloromethyl derivatives could be efficiently synthesized by the highly chemoselective platinum on carbon-catalyzed mono-dechlorination of trichloromethyl substrates in dimethylacetamide (DMA) as a specific solvent at 25 °C under a hydrogen atmosphere. Copyright
- Imanishi, Takahiro,Fujiwara, Yuta,Sawama, Yoshinari,Monguchi, Yasunari,Sajiki, Hironao
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supporting information; experimental part
p. 771 - 776
(2012/06/30)
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