77302-16-0Relevant articles and documents
Synthesis of optically active α-hydroxy carbonyl compounds by the catalytic, enantioselective oxidation if silyl enol ethers and ketene acetals with (salen)manganese(III) complexes
Adam, Waldemar,Fell, Rainer T.,Stegmann, Veit R.,Saha-M?ller, Chantu R.
, p. 708 - 714 (1998)
A set of silyl enol ethers and ketene acetals 1a-h with α- and/or β-phenyl as well as alkyl substituents of different steric bulk has been submitted to the enantioselective catalytic oxidation by chiral (salen)Mn(III) complexes 3. Highest conversion and best enantioselectivities have been obtained with bleach rather than iodosobenzene as oxygen source for the active oxo-metal species. With regard to substrate structure ee values up to 89% have been achieved for enol ethers with short and unbranched alkyl substituents at the siloxy position. While β-phenyl groups are beneficial for enantiofacial control, phenyl substituents α to the siloxy functionality result in lower ee values, while the diphenyl-substituted derivative 1d displays the lowest stereoselectivity. The fact that β- versus α-phenyl substituents exhibit not only differences in the magnitude but also in the sense (opposite absolute product configuration) of the stereoselectivity may be utilized as a valuable mechanistic probe to assess steric and electronic effects in the substrate and the catalyst as a function of the type and pattern of substitution. Our results display that sterid interactions between the substrate and the oxo-metal complex are mainly responsible for the observed stereochemical preferences. Indeed, significantly increased enantioselectivities are achieved even for the remote siloxy group when bulkier derivatives are employed. In contrast, primarily electronic effects operate in the (salen)Mn(III) catalyst 3 since electron-donating groups in the 5,5' positions of the salicylaldelhyde ligand afford higher ee values in this catalytic oxidation. The skewed side-on approach (trajectory) of the substrate onto the oxo-metal catalyst is favored, the metallaoxetane mechanism adequately accounts for the observed enantioselectivities. Herewith a synthetically valuable method for the preparation of optically active α-hydroxy carbonyl products 2 has been made available through the catalytic, enantioselective oxidation of the silyl enol ethers 1 by (salen)Mn(III) complexes.
Asymmetric cross-benzoin condensation promoted by a chiral triazolium precatalyst bearing a pyridine moiety
Soeta, Takahiro,Mizuno, So,Hatanaka, Yuichi,Ukaji, Yutaka
, p. 3430 - 3437 (2017/05/31)
Cross-benzoin condensation catalyzed by NHC, prepared from chiral triazolium salts bearing a pyridine ring, afforded α-hydroxy ketones with reasonable chemical yields and enantioselectivities. A wide range of aliphatic and aromatic aldehydes were successf
TCA cycle involved enzymes SucA and Kgd, as well as MenD: Efficient biocatalysts for asymmetric C-C bond formation
Beigi, Maryam,Waltzer, Simon,Fries, Alexander,Eggeling, Lothar,Sprenger, Georg A.,Müller, Michael
supporting information, p. 452 - 455 (2013/04/10)
Asymmetric mixed carboligation reactions of α-ketoglutarate with different aldehydes were explored with the thiamine diphosphate dependent enzymes SucA from E. coli, Kgd from Mycobacterium tuberculosis, and MenD from E. coli. All three enzymes proved to be efficient biocatalysts to selectively deliver chiral δ-hydroxy-γ-keto acids with moderate to excellent stereoselectivity. The high regioselectivity is due to the preserved role of α-ketoglutarate as acyl donor for these enzyme-catalyzed reactions.
Chiral amine-polyoxometalate hybrids as recoverable asymmetric enamine catalysts under neat and aqueous conditions
Li, Jiuyuan,Hu, Shenshen,Luo, Sanzhong,Cheng, Jin-Pei
experimental part, p. 132 - 140 (2009/08/09)
Solid acid-chiral amine hybrids have been synthesized and explored as recyclable and reusable enamine-type asymmetric catalysts. Simple chiral amine-polyoxometalate (CA-POM) hybrids were identified as the optimal catalysts to promote a range of enamine-ba
