Synthesis of N,N-bis[2-(2-pyridyl)ethyl]amino steroids and related compounds intended as chiral ligands for copper ions

Compounds with the N,N-bis[2-(2-pyridyl)ethyl]amino structure (RPY2) are us eful tridentate ligands for copper(I) ions, which can bind and activate oxy gen from the atmosphere. For diastereoselective and enantioselective oxidat ion reactions, hitherto unknown chiral ligands possessing tripodal structur es have been synthesized starting from homochiral steroids. The double Mich ael addition of primary steroidal amines and aminoalcohols to 2-vinyl pyrid ine was not very succesful. However, homochiral bidentate ligands with N-[2 -(2-pyridyl)ethyl]amino steroid structure could be obtained by this procedu re in most cases. New routes (acylation of the bidentate ligands with 2-pyr idylacetic acid followed by (BH3THF)-T-. reduction, or reductive amination of steroidal ketones, acylation and borane reduction) to the desired triden tate RPY2, also at sterically hindered positions, are described. In the las t reaction sequence,'mixed' tridentate ligands can also be obtained. Copper complexation and oxygen activation with these ligands are briefly discusse d. (C) 2000 Elsevier Science Ltd. All rights reserved.