- Asymmetric Hydrogenation of Cationic Intermediates for the Synthesis of Chiral N,O-Acetals
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For over half a century, transition-metal-catalyzed homogeneous hydrogenation has been mainly focused on neutral and readily prepared unsaturated substrates. Although the addition of molecular hydrogen to C=C, C=N, and C=O bonds represents a well-studied paradigm, the asymmetric hydrogenation of cationic species remains an underdeveloped area. In this study, we were seeking a breakthrough in asymmetric hydrogenation, with cationic intermediates as targets, and thereby anticipating applying this powerful tool to the construction of challenging chiral molecules. Under acidic conditions, both N- or O-acetylsalicylamides underwent cyclization to generate cationic intermediates, which were subsequently reduced by an iridium or rhodium hydride complex. The resulting N,O-acetals were synthesized with remarkably high enantioselectivity. This catalytic strategy exhibited high efficiency (turnover number of up to 4400) and high chemoselectivity. Mechanistic studies supported the hypothesis that a cationic intermediate was formed in situ and hydrogenated afterwards. A catalytic cycle has been proposed with hydride transfer from the iridium complex to the cationic sp2 carbon atom being the rate-determining step. A steric map of the catalyst has been created to illustrate the chiral environment, and a quantitative structure–selectivity relationship analysis showed how enantiomeric induction was achieved in this chemical transformation.
- Sun, Yongjie,Zhao, Qingyang,Wang, Heng,Yang, Tilong,Wen, Jialin,Zhang, Xumu
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supporting information
p. 11470 - 11477
(2020/08/10)
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- Amidation of carboxylic acids via the mixed carbonic carboxylic anhydrides and its application to synthesis of antidepressant (1S,2R)-tranylcypromine
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Primary amidations of carboxylic acids 1 or 3 with NH4Cl in the presence of ClCO2Et and Et3N were developed to afford the corresponding primary amides in 22% to quantitative yields. Additionally, we have applied the amidation to the preparation of various amides containing hydroxamic acids and achieved the synthesis of (1S,2R)-tranylcypromine as an antidepressant medicine via Lossen rearrangement.
- Ezawa, Tetsuya,Kawashima, Yuya,Noguchi, Takuya,Jung, Seunghee,Imai, Nobuyuki
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p. 1690 - 1699
(2017/11/14)
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- Convenient preparation of primary amides via activation of carboxylic acids with ethyl chloroformate and triethylamine under mild conditions
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Primary amides were easily prepared in 22-99% yields from the corresponding carboxylic acids 1 or 5 with NH4Cl via activation with ClCO 2Et and Et3N. The enantiomers of the corresponding primary amides of Cbz-, Boc-, or Fmoc-α-amino acids can be separated by using a chiral column.
- Noguchi, Takuya,Sekine, Masahiro,Yokoo, Yuki,Jung, Seunghee,Imai, Nobuyuki
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p. 580 - 582
(2013/07/05)
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- DI-ASPIRIN DERIVATIVES
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The invention relates to the use of di-aspirin (bis(2-carboxyphenyl)succinate) and its derivatives in the treatment of colon and colorectal cancer. It also relates to novel derivatives of di-aspirin and to a method of synthesis of the di-aspirin and its derivatives.
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Page/Page column 26-27
(2011/09/15)
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- Nitrile Sulphides. Part 7. Synthesis of Benzopyranoisothiazoles and Isothiazoloquinolines
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o-Hydroxybenzonitrile sulphide (1a), generated by thermal decarboxylation of the corresponding 1,3,4-oxathiazol-2-one, reacts with dimethyl acetylenedicarboxylate to afford methyl 4-oxo-4H-benzopyranoisothiazole-3-carboxylate (6a), from which the parent ring system (6c) can be prepared by hydrolysis and decarboxylation.The same products are formed from the acetoxy analogue (1b) via hydrolysis of isothiazole (5b). o-Acetamidobenzonitrile sulphide (1c) reacts similarly forming isothiazole (5c) and subsequently isothiazoloquinolin-4(5H)-one (7c) by hydrolysis, ring closure, and decarboxylation.Cycloadditions to ethyl cyanoformate, ethyl propiolate, and diethyl fumarate have also been examined.
- Brownsort, Peter A.,Paton, Michael
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p. 2339 - 2344
(2007/10/02)
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