Benzenesulfonic acid, 4-methyl-, compd. with pyridine (1:1) → (2S,5R/S)-1-(tert-Butoxycarbonyl)-5-ethoxypyrrolidine-2-carboxylic acid tert-butyl ester

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A solution of 12.1 g of 207 (42.1 mmol) in 100 ml of anhydrous EtOH was added with 200 mg of PPTS (0.80 mmol, 1.9 mole %) and stirred at RT overnight. Thereafter, the solvent was completely removed under vacuum, and the residue was taken up in 250 ml of a 1:2 mixture of EE/CH. After filtration over a short silica gel column, the eluate was concentrated to obtain 12.8 g of α-methoxycarbamate 45 (40.5 mmol, 96%) as a slightly yellowish oil. An analytical sample was obtained by column chromatography over silica gel (EE/CH 1:2).

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