Preparation of Optically Active α‐Amino[3]ferrocenophanes − Building Blocks for Chelate Ligands in Asymmetric Catalysis

Treatment of 1,1′‐diacetylferrocene ( 4 ) with dimethylamine and TiCl 4 yielded the unsaturated dimethylamino‐substituted [3]ferrocenophane product 5 . Its catalytic hydrogenation gave the corresponding saturated [3]ferrocenophane system 6 ( trans / cis ≈ 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 (1 R ,3 R ,5 R )‐ 10a and (1 S ,3 S ,5 R )‐ 10b [starting from ( R )‐ 9 ], their enantiomers ent ‐ 10a and ent ‐ 10b were obtained from ( S )‐ 9 , but with a poor asymmetric induction ( 10a / 10b < 2:1). Quaternization of 6 (CH 3 I) 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 (1 R ,3 R ,5 R )‐ 10a and (1 S ,3 S ,5 R )‐ 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 (1 R ,3 R )‐ 11 and (1 S ,3 S )‐ 11 , respectively, which were converted into the corresponding dimethylamino‐substituted [3]ferrocenophanes (1 R ,3 R )‐ 6 and (1 S ,3 S )‐ 6 . Each enantiomer from the following enantiomeric pairs was isolated in its pure form and characterized by X‐ray diffraction: ( R )‐ 9 /( S )‐ 9 ; (1 R ,3 R ,5 R )‐ 10a /(1 S ,3 S ,5 S )‐ 10a ; (1 R ,3 R ,5 S )‐ 10b /(1 S ,3 S ,5 R )‐ 10b ; (1 R ,3 R )‐ 11 /(1 S ,3 S )‐ 11 . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)