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Preparation of New, Optically Active 1,2‐Ferrocenyldiamine Ligands and Their Application to Ruthenium‐Catalyzed Asymmetric Transfer Hydrogenation of Ketones
Author(s) -
Fukuzawa Shinichi,
Suzuki Takashi
Publication year - 2006
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200500660
Subject(s) - chemistry , diastereomer , walden inversion , ruthenium , medicinal chemistry , catalysis , azide , transfer hydrogenation , aryl , ferrocene , lewis acids and bases , stereochemistry , organic chemistry , electrode , alkyl , electrochemistry
The treatment of ( R , R )‐1,2‐bis(1‐acetoxy‐1‐phenylmethyl)ferrocene ( 1 ) with azidotrimethylsilane in CH 2 Cl 2 in the presence of a catalytic amount of a Lewis acid such as Cu(OTf) 2 or Sc(OTf) 3 , at –40 °C for 24 h, gives a mixture of two diastereomeric ferrocenyl diazides 4 and 5 in an 80:20 ratio. The major isomer ( R , R )‐ 4 is formed with retention of configuration at both benzylic chiral centers whereas the minor isomer meso ‐( R , S )‐ 5 is formed with inversion of configuration at one of the two chiral centers. After a shorter reaction time (12 h), the ( R , R )‐ferrocenylazido acetate 6 was isolated as a single diastereomer, which gave 4 and 5 under the same conditions with almost the same ratio as with the longer reaction time. These results show that the first step of the reaction is the substitution, with retention of configuration, of the exo acetate of 1 by means of an iron‐assisted ionization, i.e., neighboring‐group participation, then the endo acetate is replaced by the azide ion with retention or inversion of configuration to give 4 or 5 , respectively. The optically active complex 4 could be converted into the corresponding ferrocenyldiamine 2 by reduction with LiAlH 4 , and its ditosylamide 8a and diacetamide 8b were isolated as stable compounds. The ferrocenyldiamine and both diamides were used as ligands in the ruthenium‐catalyzed asymmetric transfer hydrogenation of aryl ketones, and the complex with 2 gave 1‐arylethanols in good yields with up to 75 % ee .(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)