- Copper-catalysed domino silylative aldol reaction leading to stereocontrolled chiral quaternary carbons
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(Chemical Equation Presented) Asymmetric aldol reaction: A domino silylation-aldol reaction between enoyloxazolidinones and various aldehydes has been developed (see scheme). The process catalysed by a copper complex in the presence of a borosilane led to high diastereoselectivities. Yields between 59 and 90 % and d.r. values between 78:22 to 95:5 were obtained. When methacryloyloxazolidinones were used, a controlled chiral quaternary carbon was generated. BPin=4,4,5,5-tetramethyl-1,3,2dioxaborolan-2-yl.
- Welle, Alexandre,Petrignet, Julien,Tinant, Bernard,Wouters, Johan,Riant, Olivier
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supporting information; experimental part
p. 10980 - 10983
(2010/11/21)
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- Palladium(II)-Catalyzed Asymmetric Acetalization of Alkenes
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The terminal olefinic carbon of N-methaacryloyl-2-oxazolidinones is smoothly acetalized by alcohols in the presence of PdCl2 catalyst.The use of 4(S)-isopropyl-, phenyl-, and tert-butyl-2-oxazolidinones as the chiral auxiliary resulted in the formation of the corresponding (2'S)-acetals in 61, 80, and 95percent de, respectively.Reductive removal of the auxiliary with LiAlH4 followed by deacetalization produced (R)-3-hydroxy-2-methylpropanal.The enantiomer of this compound, derived from 4(R)-substituted oxazolidinones, served as a building block for synthesizing a 1β-methylcarbapenem precursor in high enantiomeric excess.In the acetalization of 3',3'-dideuteriated methacryloyl-4-isopropyloxazolidinone with MeOH, one D-atom on the terminal olefinic carbon stereoselectively migrated to the chiral center in the product acetal.On the basis of this 1,2-hydride migration and the conformational preference of the methacryloyl moiety, the reaction pathway and the mechanism of the diastereoselection are discussed.
- Hosokawa, Takahiro,Yamanaka, Toshio,Itotani, Motohiro,Murahashi, Shun-Ichi
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p. 6159 - 6167
(2007/10/03)
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