240429-85-0Relevant academic research and scientific papers
First generation cysteine- and methionine-derived oxazolidine and thiazolidine ligands for palladium-catalyzed asymmetric allylations
Schneider, Paulo H.,Schrekker, Henri S.,Silveira, Claudio C.,Wessjohann, Ludger A.,Braga, Antonio L.
, p. 2715 - 2722 (2004)
A new series of enantiopure oxazolidine-thioether and thiazolidine-alcohol ligands have been synthesized from L-cysteine, S-methyl-L-cysteine, and L-methionine in a straightforward manner that allows numerous structural variations to be formed. These types of ligands have not previously been used in asymmetric palladium-catalyzed allylations and their efficacy was explored in the reaction of rac-1,3-diphenyl-2-propenyl acetate with dimethyl malonate. The reaction proceeds in excellent yield and with good enantioselectivity. The palladium catalyst derived from N-benzyl-2,2-dimethyl-4-(2-thiapropyl) oxazolidine (12) provides the allylation product in a quantitative yield and with an enantiomeric excess of 94%. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
A new cysteine-derived ligand as catalyst for the addition of diethylzinc to aldehydes: The importance of a 'free' sulfide site for enantioselectivity
Braga, Antonio L.,Alves, Elenilson F.,Silveira, Claudio C.,Zeni, Gilson,Appelt, Helmoz R.,Wessjohann, Ludger A.
, p. 588 - 594 (2007/10/03)
New chiral sulfides and disulfides were synthesized from readily available and inexpensive cysteine by straightforward methods in order to elucidate the relative importance of the various donor atoms (N, O, S) available in free or alkylated form resulting in covalent or dative bonds to the metal, respectively. Their application in the addition of diethylzinc to aldehydes provides secondary alcohols with up to 99% ee, and S-configuration, when catalytic amounts of disulfide ligands with the ability to form an S-Zn bond were used. In contrast to this, benzyl alcohols with the opposite absolute configuration R could be achieved, albeit with decreased yield and enantioselectivity, by the use of alkylated sulfide ligands.
A new functionalized, chiral disulfide derived from L-cysteine: (R,R)- bis[(3-benzyloxazolan-4-yl)-methane] disulfide as a catalyst in the diethylzinc addition to aldehydes
Braga, Antonio L.,Appelt, Helmoz R.,Schneider, Paulo H.,Silveira, Claudio C.,Wessjohann, Ludger A.
, p. 1733 - 1738 (2007/10/03)
A new, easily accessible, chiral disulfide 3 was prepared from L- cysteine in a short synthetic sequence (Scheme 1) and applied successfully as a highly efficient catalyst for the enantioselective addition of diethyl zinc to aromatic and aliphatic aldehydes to afford the product alcohols in up to more than 99% ee. In contrast to the more common amino alcohols used in similar reactions, catalyst 3 does not have a protic hydrogen in the form of a free hydroxy group.
