Asymmetrische Synthese neuer planar- und zentral-chiraler Ferrocenylliganden

摘要

In this thesis we describe the enantioselective synthesis of mono- and di-ortho-substituted ferrocenyl diketones via our SAMP/RAMP-hydrazone method. Keystep is the stepwise diastereoselective ortho-metalation of 1,1'-bisbenzoylferrocene-bis-SAMP-hydrazone followed by trapping of various types of electrophiles. Within our studies we demonstrate the broad applicability of this method by using alkyl-, silyl-, phosphin- and sulfur electrophiles. We obtained the desired products in very good yields (85 -100%) and high diastereoselectivities (de >= 96%). The monosubstituted bis-SAMP-hydrazones prepared, could either undergo a second diastereoselective ortho-substitution under the same conditions to lead to 2,2'-substituted bis-SAMP-hydrazones or could be cleaved to produce mono-substituted 1,1'-bisbenzoylferrocenes. In case of second substitutions we applied alkylation, silylation, phosphinylation, hydroxyalkylation and sulfenylation rections in good yields (45 - 89%) and high diastereoselectivities (de >= 96%). To obtain the disubstituted diketones, it was necessary to cleave the corresponding SAMP-hydrazones. We obtained the desired products in very good yields (28 - 98%) and high diastereoselectivities (de >= 96%). Furthermore we developed an efficient asymmetric synthesis of planar chiral monosubstituted diferrocenylketones in good yields and excellent enantiomeric exesses employing the SAMP/RAMP hydrazone methodology. These compounds are versatile starting materials for further synthetic transformations. A second diastereoselective ortho-metalation without a further chiral auxiliary led to the planar chiral disubstituted diferrocenyl ketones in moderate to very good yields and moderate to excellent diastereoselectivities. Reduction using a mixed hydride of LAH and AlCl3 led to the mono- and disubstituted diferocenyl methanes without epimerisation in good to excellent yields. The application of these novel compounds as ligands in asymmetric catalysis was investigated in palladium catalyzed cross-coupling of 1-phenylethyl magnesium chloride with vinyl bromide to give 3-phenyl-1-butene in very good yields and excellent enantioselectivities. Partly these are the best results in this reaction ever described in literature.