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

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 NaBH4, BF3–OEt2, 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.

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