Cr(Salen)-catalyzed addition of 1,3-dichloropropene to aromatic aldehydes. A simple access to optically active vinyl epoxides.
[reaction: see text]. Chiral Cr(Salen) complex (1) prepared in situ from CrCl3 promotes the enantioselective addition of 1,3-dichloropropene to aromatic aldehydes in the presence of Mn as the stoichiometric reductant and Me3SiCl as a scavenger. The result
Chiral zinc-catalyzed asymmetric α-alkylallylation and α-chloroallylation of aldehydes
Two birds with one stone: In the presence of Zn(OH)2 and a chiral bipyridine ligand, racemic α-substituted allylboronates 2 reacted with aldehydes 1 (see scheme) exclusively in an α-addition fashion to afford various homoallylic alcohols 3 bear
Kobayashi, Sha,Endo, Toshimitsu,Ueno, Masaharu
supporting information; experimental part
p. 12262 - 12265
(2012/02/01)
Diastereo- and enantioselective synthesis of syn-α-vinylchlorohydrins and cis-vinylepoxides
A new method to generate chiral syn-vinylchlorohydrins and cis-vinyloxiranes is reported. Reaction of (α-haloallyl)lithiums with methoxy-9-BBN or Ipc2BOMe followed by treatment with BF3·OEt2 leads to (Z)-(γ-haloallyl)boranes which react with aldehydes to yield cis-vinylepoxides (de ≥ 90%) upon oxidative workup. Alternatively, addition of ethanolamine to the allylboration product yields syn-α-halohydrins (de ≥ 90%) that are also easily cyclized to cis-vinylepoxides. Extension of this protocol using [(Z)-γ-chloroallyl]BIpc2 leads to chiral syn-α-chlorohydrins and cis-vinylepoxides in high de (≥90%) and ee (90-99%). Enantioselectivity of reactions of chiral (Z)-(γ-chloroallyl)boranes with aldehydes are more sensitive to reaction conditions than enantioselectivity of reactions of other α-or γ-substituted allylboranes. The effects of proportion of BP3·OEt2 and the relative efficacies of LiNR2 bases on diastereo- and enantioselectivity of the chloroallylation are reported.
Hu, Shaojing,Jayaraman, Seetharaman,Oehlschlager, Allan C.
p. 7513 - 7520
(2007/10/03)
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