| abstract |
Prodn. of optically active piperazine-2-carboxylic acid derivs. of formula (I) comprises asymmetric hydrogenation of the corresp. 1,4,5,6-tetrahydropyrazine-2-carboxylic acid derivs. of formula (II) in the presence of an optically active rhodium, ruthenium and/or iridium complex catalyst: R<1>, R<2> = H, 1-4C alkyl, opt. substd. 1-6C alkanoyl, 2-6C perfluoroalkanoyl, aroyl, aralkyl, 2-7C alkoxycarbonyl, aryloxycarbonyl, CONH2 or N-protecting gps.; X = H, 1-6C alkoxy or NR<3>R<4>; R<3>, R<4> = H, 1-6C alkyl, 3-6C cycloalkyl, aryl or N-protecting gps.; or NR<3>R<4> = satd. 5- or 6-membered ring; or R<3> = H and R<4> = CH(R<5>)COOR<6>; R<5> = H or an amino acid side chain; R<6> = H, 1-4C alkyl or aryl. Also claimed are (a) optically active (I) where one of R<1> and R<2> is 1-6C alkanoyl or 2-6C perfluoroalkanoyl, and their enantiomer mixts.; and (b) (II) provided that R<1> and R<2> are not both H. |