Epimeric Pyrroloimidazolone Auxiliaries in the Diastereoselective Synthesis of Chiral N-Ferrocenyl/N-Phenyl Ligands and Arene-Chromium Tricarbonyl Complexes
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This thesis describes the synthesis and use of an N-based L-proline derived chiral auxiliary/directing group for selective synthesis of planar chiral and central chiral products. A series of planar chiral ferrocenes were prepared, and converted to chloroimidazoliums and complexed to palladium via oxidative addition. In addition to this, a centrally chiral Ir(I) catalyst was prepared for the purpose of evaluating the importance of planar chirality for the induction of enantioselectivity in the Ir(I) catalyzed hydrogenations of 2-substituted quinolines. A lower enantioselectivity was observed, allowing the conclusion that planar chirality does contribute to the enantioselectivity. The pyrroloimidazolone directing group used to induce high diastereoselectivity in ferrocene lithiations (>95:5 dr) has been applied (with minor modifications) towards the diastereoselective lithiation of η6-arene chromium tricarbonyl complexes. The anti-epimer of the pyrroloimidazolone auxiliary undergoes pro-R lithiation in >95:5 dr. The syn-epimer of this auxiliary undergoes pro-S lithiation in >95:5 dr. The origin of selectivity is believed to be caused by a conformational bias exerted by the O-group. The selectivity of lithiations, and stereochemistry of all the products has been confirmed by a combination of X-ray analysis, transmetalation and deuteration experiments and by the preparation and comparison of solely planar chiral enantiomers.