Preparation of Optically Active alpha-Amino[3] ferrocenophanes-Building Blocks for Chelate Ligands in Asymmetric Catalysis

摘要

Treatment of 1,1'-diacetylferrocene (4) with dimethylamine and TiCl_4 yielded the unsaturated dimethyalmino-substituted [3] ferrocenophane product 15.Its catalytic hydrogenation gave the corresponding saturated [3] ferrocenophane system 6 (trans/cis approx = 7:1).The rac-[3] ferrocenophane amine 6 was partially resolved (to ca.80% ee) by means of L-or D-O,O'-dibenzoyltartrate salt formation.Treatment of 4 with the pure (R)-or (S)-methyl(1-phenylethyl)amine (8)/TiCl_4 gave the corresponding optically active unsaturated [3] ferrocenophane amines (R)-(+)-9 and (S)-(-)-9,respectively.Their catalytic hydrogenation again proceeded trans-selectively,giving the corresponding saturated diastereomeric [3] ferrocenophane amines (1R,3R,5R)-10a and (1S,3S,5R)-10b [starting from (R)-9],their enantionmers ent-10a and ent-10b were obtained from (S)-9,but with a poor asymmetric induction (10a/10b<2:1).Quaternization of 6 (CH_3I) followed by amine exchange using (R)-or (S)-methyl (1-phenylethyl)-amine (8),respectively,proceeded with overall retention.Subsequent chromatographic separation gave the pure diastereoisomers (1R,3R,5R)-10a and (1S,3S,5R)-10b [from (R)-8,ent-10a and ent-10b from (S)-8] in >60% yield.Subsequently,the benzylic (1-phenylethyl) auxiliary was removed from the nitrogen atom by catalytic hydrogenolysis to yield the enantiomerically pure (>98%) ([3]ferrocenophanyl)-methylamines (1R,3R)-11 and (1S,3S)-11,respectively,which were converted into thecorresponding dimethylamino-substituted [3] ferrocenophanes (1R,3R)-6.Each enantiomer from the following enantiomeric pairs was isolated in its pure form and characterized by X-ray diffraction:(R)-9/(S)-9;(1R,3R,5R)-10a/(1S,3S,5S)-10a;(1R,3R,5S)-10b/(1S,3S,5R)-10b;(1R,3R)-11/(1S,3S)-11.