Methyl iodide → 2-Methyl 1-(phenylmethyl) (2S,4R)-4-hydroxy-1,2-pyrrolidinedicarboxylate

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Reaction Steps

A solution of N-benzyloxycarbonyl-4-hydroxy-L-trans-proline 9 (47.5 g; 179 mmol) in anhydrous methanol (900 ml) is adjusted to pH=9.0-9.5 using caesium carbonate. The mixture is subsequently stirred at room temperature for 30 min., and then concentrated. After having been dried for 30 minutes under high vacuum, the residue is taken up in anhydrous N,N-dimethylformamide (900 ml). Iodomethane (28.0 g; 197 mmol) is added, and the mixture is stirred at room temperature for 21 h. The solution is concentrated, and the residue is subsequently distilled repeatedly with toluene, taken up in chloroform (1.8 l), and then extracted by shaking once with each of water and a 10% solution of sodium hydrogen carbonate, and once again with water (600 ml on each occasion). The organic phase is dried (magnesium sulphate) and concentrated. Yield: 50.0 g (quantitative).

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