The synthesis of chiral Câ†3-symmetric systems
Chapter one is an overall introduction reviewing the applications of compounds possessing rotational symmetry, in particular their role as asymmetric reagents/catalysts in various reactions. The attempted syntheses of two different types of C3-symmetric homochiral triols are described in chapter two. Unfunctionalised and functionalised triamides were synthesised from the corresponding amine and 1,3,5-benzenetricarbonyl trichloride. Unfunctionalised N-substituted 1,3,5-triazacychlohexanes (triazines) were synthesised from the corresponding amine and formaldehyde, however reactions between chiral amino alcohols and formaldehyde failed to give the desired trihydroxy triazines. Chapter three describes the syntheses of a range of unfunctionalised chiral C3-symmetric compounds, as well as a review of C3-symmetric systems as host molecules. The successful synthesis of a range of unfunctionalised triethrs was carried out by reacting 1,3,5-tris(bromomehyl)mesitylene with some selected terpenes and other alcohols. Their role as host molecules was investigated, however they failed to bind with any of the various metals that were used. Their asymmetric induction capabilities were also tested when one of the triethers was used as a catalyst in the Et2Zn/aldehyde reaction. The desired alcohol was indeed isolated, however it was found by 1H nmr of the Mosher's ester to be a reacemic mixture. In chapter four the synthesis of the unfunctionalised triethers that was described in chapter three was extended to the synthesis of C3-symmetric triethers containing functional groups. A range of tridentate ligands were synthesised containing either amino, ester, keto or hydroxyl terminal groups. In addition to these, trihydroxy ligands containing amino linkages in place of ethereal linkages were also synthesised. From these compounds three of the trihydroxy ligands were used in complexation reactions with Sn, Ti, Si, Ni, and Cu. The reactions using Si, Ni and Cu failed to give the desired complexes. However, strong evidence was obtained for the existence of the desired Sn and Ti complexes. Once again using the Et2Zn/aldehyde reaction preliminary asymmetric induction studies were carried out using one of the Ti complexes. The reaction showed some selectivity in favour of the R enantiomer. Chapter four also describes the syntheses of some hexadentate ligands, in particular the synthesis of a chiral C3-symmetric hexol, a C3-symmetric ligand containing three β keto-ester groups, and also a 1,3-diketo derivative.