Double stereoselective coordination of chiral N,S ligands: Synthesis, coordination chemistry and utilization in Pd-catalyzed allylic alkylation

Recent Advances in Enantioselective Pd-Catalyzed Allylic Substitution: From Design to Applications

This Review compiles the evolution, mechanistic understanding, and more recent advances in enantioselective Pd-catalyzed allylic substitution and decarboxylative and oxidative allylic substitutions. For each reaction, the catalytic data, as well as examples of their application to the synthesis of more complex molecules, are collected. Sections in which we discuss key mechanistic aspects for high selectivity and a comparison with other metals (with advantages and disadvantages) are also included. For Pd-catalyzed asymmetric allylic substitution, the catalytic data are grouped according to the type of nucleophile employed. Because of the prominent position of the use of stabilized carbon nucleophiles and heteronucleophiles, many chiral ligands have been developed. To better compare the results, they are presented grouped by ligand types. Pd-catalyzed asymmetric decarboxylative reactions are mainly promoted by PHOX or Trost ligands, which justifies organizing this section in chronological order. For asymmetric oxidative allylic substitution the results are grouped according to the type of nucleophile used.

Tuning Rh(II)-catalysed cyclopropanation with tethered thioether ligands

Dirhodium(ii) paddlewheel complexes have high utility in diazo-mediated cyclopropanation reactions and ethyl diazoacetate is one of the most commonly used diazo compounds in this reaction. In this study, we report our efforts to use tethered thioether ligands to tune the reactivity of RhII-carbene mediated cyclopropanation of olefins with ethyl diazoacetate. Microwave methods enabled the synthesis of a family of RhII complexes in which tethered thioether moieties were coordinated to axial sites of the complex. Different tether lengths and thioether substituents were screened to optimise cyclopropane yields and minimise side product formation. Furthermore, good yields were obtained when equimolar diazo and olefin were used. Structural and spectroscopic investigation revealed that tethered thioethers changed the electronic structure of the rhodium core, which was instrumental in the performance of the catalysts. Computational modelling of the catalysts provided further support that the tethered thioethers were responsible for increased yields.