Practical synthetic process for enantiopure 1-benzyl-3-hydroxypyrrolidine

Abstract

The synthesis of ( S)-1-benzyl-3-hydroxypyrrolidine ( S)- 5 comprised the asymmetric hydroboration of 1-benzyl-3-pyrroline 4, followed by oxidation and chiral purification via diastereomeric salt formation. The asymmetric borane reagent was generated ‘in situ’ from NaBH 4, BF 3–OEt 2, and (+)-α-pinene 1 (85% ee) and reacted with 4, prepared from cis-1,4-butenediol 3, to give crude product ( S)- 5. The following chiral purification via diastereomeric salt formation proceeded to afford ( S)- 5 with >99% ee. The optimized process was successfully scaled up to an industrial scale to produce a 252 kg batch of ( S)- 5.