Convenient Procedures for the Asymmetric Reduction of 1,4-Diphenylbutane-1,4-dione and Synthesis of 2,5-Diphenylpyrrolidine Derivatives

Asymmetric reduction of 1,4-diphenylbutane-1,4-dione (1) was carried out using the reducing agents NaBH 4 , BH 3 .THF, and PhNEt 2 .BH 3 in combination with the chiral reagents (S)-(-)-α,α-diphenyl-2-pyrrolidinemethanol (4) or (S)-proline (5), in the presence of TMSCI or B(OMe) 3 under various conditions to obtain the corresponding 1,4-diol 2 in 52% to 97% ee. The chiral 1,4-diol 2 was converted to various C 2 -symmetric (2S,5S)-2,5-diphenyl-pyrrolidine derivatives 3a-e (45 to 75% yield) via the corresponding dimesylate prepared using MsCl and Et 3 N.