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

• Published in: European journal of inorganic chemistry 2003-12, Vol.2003 (23), p.4261-4261
• Main Authors: Liptau, Patrick, Tebben, Ludger, Kehr, Gerald, Wibbeling, Birgit, Fröhlich, Roland, Erker, Gerhard
• Format: Article
• Language: English
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.200300782

Treatment of 1,1′‐diacetylferrocene (4) with dimethylamine and TiCl4 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)/TiCl4 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 enantiomers ent‐10a and ent‐10b were obtained from (S)‐9, but with a poor asymmetric induction (10a/10b < 2:1). Quaternization of 6 (CH3I) 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 the corresponding dimethylamino‐substituted [3]ferrocenophanes (1R,3R)‐6 and (1S,3S)‐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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)