- 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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- HIGHLY STEREOSELECTIVE REFORMATSKY REACTIONS OF 3-(2-BROMOPROPIONYL)-2-OXAZOLIDONE DERIVATIVES WITH VARIOUS ALDEHYDES
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The Reformatsky reactions of 3-(2-bromopropionyl)-2-oxazolidone derivatives with various aldehydes were investigated to elucidate the effects of substituents in the 2-oxazolidone moieties on their diastereoselectivities.The highest 2,3-syn-diastereoselect
- Ito, Yoshio,Terashima, Shiro
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p. 2821 - 2834
(2007/10/02)
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- A HIGHLY STEREOSELECTIVE SYNTHESIS OF ALDOLS EMPLOYING THE REFORMATSKY REACTION OF 3-(2-BROMOPROPIONYL)-2-OXAZOLIDONE DERIVATIVES WITH VARIOUS ALDEHYDES
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The title reactions of sterically crowded 2-oxazolidone derivatives with achiral aldehydes in the presence of zinc dust were found to give various 2,3-syn-aldols as major products (at most, 2,3-syn:2,3-anti=98:2).While a 2,3-syn-3,4-syn-aldol could be sim
- Ito, Yoshio,Terashima, Shiro
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p. 6629 - 6632
(2007/10/02)
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