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

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Abstract
Asymmetric reduction of 1,4-diphenylbutane-1,4-dione (1) was carried out using the reducing agents NaBH4, BH3·THF, and PhΝEt2·ΒΗ3 in combination with the chiral reagents (S)-(-)-α,α-diphenyl-2-pyrrolidinemethanol (4) or (S)-proline (5), in the presence of TMSCl 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 C2-symmetric (2S,5S)-2,5-diphenyl­pyrrol­idine derivatives 3a-e (45 to 75% yield) via the corresponding dimesylate prepared using MsCl and Et3N.