Trost BM *,
Van Vranken DL,
Bingel C.
Stanford University, USA
A Modular Approach for Ligand Design for Asymmetric Allylic Alkylations via Enantioselective
Palladium-Catalyzed Ionizations.
J. Am. Chem. Soc. 1992;
114: 9327-9343
DOI:
10.1021/ja00050a013
Keywords
Trost ligands - palladium - enantioselective - rational design
Significance
Over three decades ago, the Trost group outlined their rational ligand design in the
development of what are now called the ‘Trost ligands’. These ligands have applications
in enantioselective allylations using palladium as a catalyst. In this case the Trost
group investigated the intramolecular cyclization of a symmetric, prochiral dicarbamate.
All the reported ligands use 2-(diphenylphosphino)benzoic acid (DPPBA) as the phosphine
source.
Comment
Initially, Trost used ionic salts by reacting chiral amine bases with DPPBA, resulting
in minimal success. Improvements were observed when a covalent ester bond was used
for monodentate ligands. They next prepared C
2-symmetric bidentate ester ligands and observed a large increase in the ee value.
Restricting rotation of the backbone also improved the ee value. Lastly, switching
to C
2-symmetric diamide ligands with large dihedral angles resulted in high enantioselectivities
of the products.
