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A 500-mL, round-bottomed flask was charged with methyl N-trityl-L-threoninate (3.75 g, 10.0 mmol), benzoic acid (2.44 g, 20.0 mmol) and triphenylphosphine (5.24 g, 20.0 mmol). Anhydrous THF (50 mL) was added and the solution was cooled to 0° C. under N2 with stirring. A 40% solution of diethylazodicarboxylate in toluene (9.06 mL, 20.0 mmol) was added dropwise and the reaction mixture was allowed to warm to ambient temperature overnight. The reaction mixture was treated with 50 mL of ethyl acetate and 50 mL of saturated aqueous NaHCO3 solution. The layers were separated and the organic portion was washed successively with H2O and brine, dried over Na2SO4, filtered and concentrated under reduced pressure to give a yellow syrup. The yellow syrup was dissolved in 25 mL of Et2O and then treated with hexanes until a white precipitate formed. The solid was removed by filtration and the filtrate was concentrated to give a yellow oil. Chromatography (SiO2, 33-100% CH2Cl2/hexanes) gave 1.24 g of methyl O-benzoyl-N-trityl-L-allothreoninate as a colorless solid.

1. temperatureto warm to ambient temperature overnight
2. customThe layers were separated
3. washthe organic portion was washed successively with H2O and brine
4. dry with materialdried over Na2SO4
5. filtrationfiltered
6. concentrationconcentrated under reduced pressure
7. customto give a yellow syrup
8. customformed
9. customThe solid was removed by filtration
10. concentrationthe filtrate was concentrated
11. customto give a yellow oil