The enantioselectiveaddition of organozincreagents to aromatic and aliphatic aldehydes 1 gives secondary alcohols 2 with excellent enantioselectivities in high yields through the catalytic use of (R)-3,3′-bis(diphenylphosphinoyl)-BINOL (3) or (R)-3,3′-bis(diphenylthiophosphinoyl)-BINOL (4) without Ti(IV) complexes. The coordination of the O or S atom of a (thio)phosphinoyl group bearing a BINOL backbone
Chiral bis(amino alcohol)oxalamides as ligands for asymmetric catalysis. Ti(IV) catalyzed enantioselective addition of diethylzinc to aldehydes
作者:Gonzalo Blay、Isabel Fernández、Alícia Marco-Aleixandre、José R. Pedro
DOI:10.1016/j.tetasy.2005.01.039
日期:2005.3
Several chiral bis(aminoalcohol)oxalamides with C2-symmetry have been prepared and used as ligands for the enantioselectiveaddition of diethylzinc to aromatic and aliphatic aldehydes. The reaction proceeds in the presence of titanium isopropoxide to give the corresponding (S)-alcohols with ee up to 78%. In the absence of Ti(IV), the alcohols with the opposite configuration are obtained.
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.
Synthesis of novel chiral tridentate aminophenol ligands for enantioselective addition of diethylzinc to aldehydes
作者:Xiao-Feng Yang、Takuji Hirose、Guang-You Zhang
DOI:10.1016/j.tetasy.2008.06.027
日期:2008.7
Novelchiral tridentate aminophenol ligand (S)-3a was obtained by a Mannich-type reaction of cresol, paraformaldehyde, and (S)-1-(2-methoxyphenyl)-2-methylpropan-1-amine followed by a deprotection step. This tridentate aminophenol ligand shows high yield and enantioselectivity in the diethylzincadditions to a broad range of substrates, including alkyl, aryl, and α,β-unsaturated aldehydes.
Synthesis of new chiral imidazolidine disulfides derived from l-cystine and their application in the enantioselective addition of diethylzinc to aldehydes
作者:Antonio L Braga、Fabrı́cio Vargas、Claudio C Silveira、Leandro H de Andrade
DOI:10.1016/s0040-4039(02)00300-3
日期:2002.3
Several chiral imidazolidine disulfides 4a-d derived from L-cystine have been synthesized. These ligands have been applied as chiral catalysts in the asymmetric addition of diethylzinc to aldehydes. The best results were obtained by employing 5 mol%,, of imidazolidine disulfide 4a, and chiral secondary alcohols were obtained in up to 91% e.e. (C) 2002 Elsevier Science Ltd. All rights reserved.