302800-27-7Relevant academic research and scientific papers
Asymmetric michael reactions on polymeric support: Auxiliary immobilization and stereoselective construction of quaternary stereocenters
Kreidler, Burkard,Baro, Angelika,Christoffers, Jens
, p. 5339 - 5348 (2007/10/03)
Several strategies for the immobilization of a L-valine-derived auxiliary on a Merrifield resin and on poly(ethylene glycol) are reported. The latter is shown to work excellently in asymmetric copper(II)-catalyzed Michael reactions of cyclic β-oxo esters 2 with methyl vinyl ketone (4), yielding the corresponding addition products 5 with quaternary stereocenter in selectivities of 97-99 % ee. The PEG-supported auxiliary 1d can be precipitated from diethyl ether solutions and reused. A sulfur-containing β-oxo ester 2c was prepared in 92 % yield by a DMAP-catalyzed transesterification method in order to detect enamine formation on solid support. The sulfur content can be used as an additional parameter in combustion analysis and therefore, may act as a diagnostic probe for enamine formation. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.
New auxiliaries for copper-catalyzed asymmetric Michael reactions: Generation of quaternary stereocenters at room temperature
Christoffers, Jens,Mann, Alexander
, p. 1014 - 1027 (2007/10/03)
Dialkyl amides of L-valine, L-isoleucine, and L-tert-leucine (2) are excellent chiral auxiliaries for the construction of quaternary stereocenters at ambient temperature. Enaminoesters 3, prepared from these auxiliaries 2 and Michael donors 1. undergo a copper-catalyzed asymmetric Michael reaction with methyl vinyl ketone (MVK, 4) to afford products 5 in 70-90% yield and 90-99% ee (enantiomeric excess). The exclusion of moisture or oxygen is not necessary. The auxiliaries 2 are readily available by standard procedures. After workup they can be recovered almost quantitatively.
New chiral auxiliaries for the construction of quaternary stereocenters by copper-catalyzed Michael reactions
Christoffers, Jens,Mann, Alexander
, p. 2752 - 2754 (2007/10/03)
The construction of quaternary stereocenters with 95-99% ee at ambient temperatures can be achieved by a copper-catalyzed Michael reaction with the application of α-amino acid amides as chiral auxiliaries [Eq. (1)]. These amides can be obtained in a few steps from the α-amino acids with standard transformations and, after the Michael reaction, they can be quantitatively recovered. Exclusion of water and oxygen is not necessary.
