(1S,2R)-(+)-ephedrine → Ephedrine

Beteiligte Stoffe

Reaktionsschritte

(R,S)-2-methoxy-2-(2-methoxyphenyl)acetic acid (20.75 g, 105.9 mM) was dissolved in hot ethanol (53 mL) and added quickly to a vigorously stirred, hot solution of (1S,2R)-(+)-ephedrine (17.5 g, 105.9 mM) in ethanol (50 mL). The mixture was allowed to cool to ambient temperature. The white solid obtained was collected by filtration and recrystallised from ethanol to give a crystalline ephedrine salt (15.65 g). This salt was dissolved in water (150 mL). The solution was acidified by adding 1 equivalent of M hydrochloric acid (43 mL) and then extracted with ethyl acetate (2×100 mL). The extracts were washed with water, then with saturated sodium chloride solution, dried (MgSO4) and the solvent evaporated to give (+)-2-methoxy-2-(2-methoxyphenyl)acetic acid as an oil, which slowly crystallised to give solid (8.0 g), 21 [α]D =+151.8° (c=1, Et0H); optical purity 97.6% e.e. [by NMR analysis using the NMR shift reagent (R)-(-)-TFAE].

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