carbohydrates as ligands for asymmetric catalysis
benessere, vincenzo (2010) carbohydrates as ligands for asymmetric catalysis. [Tesi di dottorato] (Inedito)
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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.
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