Carbohydrates as ligands for asymmetric catalysis

Homogeneous enantioselective catalysis is a fundamental technology for the production of fine chemicals. Beside the choice of the active metal, crucial for its effective application is the accurate design of the chiral ligand, which must exhibit a suited and well-defined structure for orienting the stereochemistry of the reaction. Accordingly, in 2002 Jacobsen indicated as “privileged” a few selected ligands of wide and proven applicability. Over the years, this original class of privileged ligands has been gradually extended to include other effective structures, and in 2008 the Aldrich Chemical Company has reviewed an entire bouquet comprising more than 30 structures. A strategy from our group is focussed on the attainment of effective chiral ligands by simple and immediate derivatization of common carbohydrates, e.g. D-glucose. This successful approach5 has produced the modular ligands’ library naplephos, which combines the essential structural motifs of the “privileged” ligands based on 1,2-trans-cyclohexanediamine with increased flexibility and accessibility. In fact, by proper choice of the R residue, the basic structure naplephos has been already effectively adapted, to two different enantioselective processes, affording in all cases the chiral product in high ee’s. In this report we describe its successful application in another relevant reaction, i.e. the asymmetric allylic alkylation (AAA), which demonstrates the versatility of the structure and its aptitude to afford chiral ligands of broad and established applicability. Also Mo AAA and multiphase catalysis are presented in this thesis

Rational design of pseudo-enantiomeric libraries of ligands based on pyranoses for application in asymmetric catalysis

This review deals with the solution given by synthetic chemists to overcome the problem of access to both enantiomers of a given process when carbohydrates are used as ligands. Indeed, although sugars are stereochemically rich compounds, and derived from one of the most abundant renewable material, their use in asymmetric catalysis has been limited by the fact that most of them have D-configuration. This review explains the concept of pseudo-enantiomeric ligands, and collects examples based on pyranoses, by describing their relevant use in asymmetric catalysis