- Diastereoselective bromodifluoromethylation of chiral imide enolates via insertion of difluorocarbene
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The bromodifluoromethylation of lithium enolates of chiral N-acyloxazolidinones via the insertion of difluorocarbene proceeds with good diastereomeric excess (68-92% de).
- Iseki, Katsuhiko,Asada, Daisuke,Takahashi, Mie,Nagai, Takabumi,Kobayashi, Yoshiro
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- Asymmetric zinc-Reformatsky reaction of Evans chiral imide with acetophenones and its application to the stereoselective synthesis of triazole antifungal agents
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The Ni(acac)2 catalytic ZnEt2-mediated asymmetric Reformatsky-type reaction of Evans chiral imide with various acetophenones was studied. The chiral imido zinc enolate, which was formed through the metal-halogen exchange reaction of
- Yu, Luo-Ting,Ho, Meng-Tsung,Chang, Ching-Yao,Yang, Teng-Kuei
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p. 949 - 962
(2008/02/03)
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- An Activated Germanium Metal-Promoted, Highly Diastereoselective Reformatsky Reaction
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Activated germanium metal, prepared by the reduction of germanium(II) iodide with potassium metal, was found to promote the Reformatsky reaction effectively under mild conditions. In the presence of activated germanium metal, the reactions of α-bromo ketones 2a and 2b and α-bromo imides 2e and 2f with benzaldehyde (1a) proceeded smoothly to give the corresponding β-hydroxy carbonyl compounds 3a, 3b, 3e and 3f, respectively, in good yields and with good syn diastereo- selectivity. The activated germanium metal-promoted, asymmetric Reformatsky reaction of enantiomerically pure-oxazolidinone derivatives 2g-j with various aldehydes 1a-d was also examined; the highest diastereoselectivity was achieved when (1S,2R)-2-amino-1,2-diphenylethanol- derived 2j was used as the Reformatsky donor. The excellent diastereoselectivity could be explained in terms of the formation of a chairlike, six-membered transition state between the aldehyde and enolate as in the Zimmerman-Traxler model. A single recrystallization of the Reformatsky adducts, followed by hydrolysis and subsequent esterification, led to enantiomerically pure methyl 3-hydroxy- 2-methylalkanoates 10j-m, with almost quantitative recovery of the enantiomerically pure 2-oxazolidinone 14.
- Kagoshima, Hirotaka,Hashimoto, Yukihiko,Oguro, Dai,Saigo, Kazuhiko
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p. 691 - 697
(2007/10/03)
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- The chromium-reformatsky reaction: Anti-selective evans-type aldol reactions with excellent inverse induction at ambient temperature
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anti-Aldol products are available in a two step, one pot reaction of 4-substituted oxazolidone, 2-bromopropionyl halide, chromium dichloride and an aldehyde. The diastereofacial selection (induction) is opposite to those of boron Evans enolates, i.e. the
- Gabriel, Tobias,Wessjohann, Ludger
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p. 4387 - 4388
(2007/10/03)
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- Heterocyclic compounds and their production
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A compound of the formula: STR1 wherein R1, R2, R3 and R4 are each a hydrogen atom, a lower alkyl group, an ar(lower)alkyl group or an aryl group, or R1 and R2 may be combined together to f
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- Highly stereocontrolled synthesis of the 1β-methylcarbapenem key intermediate by the Reformatsky reaction of 3-(2-bromopropionyl)-2-oxazolidone derivatives with a 4-acetoxy-2-azetidinone
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The key synthetic intermediate (4) of 1β-methylcarbapenems (1~3) was efficiently synthesized by employing highly stereocontrolled Reformatsky reaction (C4-alkylation) of 3-(2-bromopropionyl)-2-oxazolidone derivatives (6) with (3R,4R)-4-acetoxy-3-[(R)-1-(t-butyldimethylsilyloxy)ethyl]-2-azetidino ne (5) in the presence of zinc dust followed by removal of 2-oxazolidone moieties. The best diastereoselectivity (β:α = 95:5) could be realized by uses of sterically crowded achiral 2-oxazolidone derivatives such as 4,4-dimethyl-, 4,4,5,5-tetramethyl, and 4,4-dibutyl-5,5-pentamethylene-2-oxazolidone and higher reaction temperatures (refluxing tetrahydrofran). The remarkable diastereoselectivities observed for the Reformatsky reactions could be explained by means of the weakly chelating transition state models.
- Ito,Sasaki,Tamoto,Sunagawa,Terashima
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p. 2801 - 2820
(2007/10/02)
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