Synthesis of enantiopure phthalides including 3‐butylphthalide, a fragrance component of celery oil, and determination of their absolute configurations

Enantiopure phthalides 2 and 5 – 8 were synthesized via enantioresolution of the corresponding alcohols with a chiral auxiliary of camphorsultam dichlorophthalic acid, (1 S ,2 R ,4 R )‐(−)‐CSDP acid 3, followed by solvolysis with KOH in MeOH and the catalytic oxidation of chiral glycols with iridium complex 28. The absolute configurations of phthalides 2 and 5 – 8 were determined by applying the 1 H‐NMR anisotropy method of MαNP acid ( 4 ), 2‐methoxy‐2‐(1‐naphthyl)propionic acid, to the chiral synthetic precursory alcohols. In the case of 3‐phenylphthalide ( R )‐(−)‐ 7 , the absolute configuration determined by the 1 H‐NMR anisotropy method using MαNP acid 4 agreed with that by the X‐ray crystallographic method. By applying these methods, 3‐butylphthalide ( S )‐(−)‐ 2, a fragrance component of essential oil of celery, has been synthesized in an enantiopure form, and its absolute configuration was unambiguously determined. Chirality 17:218–232, 2005. © 2005 Wiley‐Liss, Inc.