Synthesis of enantiopure 1,1 '-(1-dimethylamino-propanediyl)ferrocene via a highly diastereoselective imine reduction

1,1'-(1-Oxo-propanediyl)ferrocene 4 reacts with (S)-(-)-1-(1-naphthylethyl) amine to give the corresponding syn imine exclusively which undergoes a hig hly diastereoselective reduction with sodium borohydride to give the diaste reomerically pure (R,S)-(+)-amine 6. Conversion of 6 leads in three steps t o the final product (R)-(+)-1,1'-(1-dimethylamino-propanediyl)ferrocene 2 i n 53% overall yield (based on J) and in >98% e.e. Use of (S)-(-)1-phenyleth ylamine as the chiral auxiliary leads to an 84: 16 mixture of syn),) and an ti imines. After reduction and separation of the resulting diastereomers th e major isomer (R,S)-(-)-10 can also be converted to the final product (R)- (+)-2 in 55% overall yield (based on 4) and in >98% e.e. (C) 2000 Elsevier Science Ltd. All rights reserved.