Highly stereoselective metal-free catalytic reduction of Lmines: An easy entry to enantiomerically pure amines and natural And Unnatural α-amino esters
A highly efficient catalytic stereoselective ketlmlne reduction is described. The combination of an Inexpensive chiral organocatalyst, easily prepared In a single step, and of a very cheap removable chiral auxiliary allowed us to obtain enantlomerlcally pure amino compounds. The methodology allowed synthesis of chiral secondary and primary amines and natural and unnatural amino esters In high yields often with total control of the absolute stereochemistry.
Synthesis of aryl glycines by the α arylation of weinreb amides
(Chemical Equation Presented) A rare example of the umpolung of an enolate forms the basis of the title reaction. In this procedure, a Grignard reagent is added to the iminium ion formed from the Weinreb amide upon treatment with a base (see scheme). When a chiral amide was used as the starting material, the nucleophilic addition proceeded with high diastereoselectivity. LDA = lithium diisopropylamide.
Hirner, Sebastian,Panknin, Olaf,Edefuhr, Magnus,Somfai, Peter
p. 1907 - 1909
(2008/12/22)
Synthesis of α-amino acids by umpolung of weinreb amide enolates
An efficient and diastereoselective synthesis of α-amino acids from readily available starting materials has been developed. The key feature of this reaction is an umpolung of a glycine-derived enolate, providing an alternative approach for the synthesis of α-amino acids. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
Hirner, Sebastian,Kirchner, Donata K.,Somfai, Peter
experimental part
p. 5583 - 5589
(2009/05/11)
Diastereoselective addition of higher order cuprates and zinc-copper reagents to imines derived from (S)-1-phenylethylamine
The diastereoselective addition of higher order (H.O.) cuprates and zinc-copper reagents to aliphatic and aromatic chiral imines derived from (S)-1-phenylethylamine was examined. Aliphatic chiral imines react with (Allyl)2CuCNLi2 and (n-Bu)2Cu(CN)Li2 in the presence of BF3-Et2O and Me3SiCl in high diastereoselection, while c-C6H11Cu(CN)ZnI and AllylCu(CN)ZnBr afford chiral amines in comparable yields without additives. Moreover the synthesis of a key intermediate towards a δ-amino-acid was reported.