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A solution of 4-tert-butyl 1-methyl 2-(4-chlorophenyl)succinate (14.3 g, 47.7 mmol) in DCM (75 mL) was treated with neat TFA (75 mL) at room temperature. The mixture was stirred for five hours to completion, after which the reaction mixture was concentrated and dried in vacuo overnight to afford a white solid. The solid was suspended in toluene (160 mL), cooled to 0° C., and treated successively with diphenylphosphoryl azide (11.2 mL, 52.1 mmol) and triethylamine (13.2 mL, 94.7 mmol). The reaction mixture (homogeneous) was allowed to warm to room temperature and stirred for four hours to completion. The solution was quenched with 1% citric acid solution and extracted with EtOAc (3×). The combined organic portion washed with brine, dried over Na2SO4, filtered, and concentrated in vacuo to give a light brown oil. The crude azide was dissolved in tert-butanol (160 mL), treated with neat SnCl4 (1.0M solution, 2.37 mL, 2.37 mmol), and carefully heated to 90° C. with evolution of nitrogen. The mixture was stirred at 90° C. for 2.5 hours and cooled to room temperature. The solution was quenched with saturated NaHCO3 solution and then concentrated. The oily mixture was extracted with EtOAc (3×), and the combined organic portion washed with brine, dried over MgSO4, filtered, and concentrated in vacuo. The residue was purified by on silica gel (4:1 hexanes:EtOAc) to afford the methyl 3-(tert-butoxycarbonylamino)-2-(4-chlorophenyl)propanoate as a pale yellow oil (11.7 g, 79%). 1H NMR (CDCl3, 400 MHz) δ 7.31 (d, J=8.0 Hz, 2H), 7.20 (d, J=8.0 Hz, 2H), 4.86 (br s, 1H), 3.88 (m, 1H), 3.69 (s, 3H), 3.58 (m, 1H), 3.49 (m, 1H), 1.42 (s, 9H).

1. concentrationafter which the reaction mixture was concentrated
2. customdried in vacuo overnight
3. customto afford a white solid
4. temperatureto warm to room temperature
5. stirringstirred for four hours to completion
6. customThe solution was quenched with 1% citric acid solution
7. extractionextracted with EtOAc (3×)
8. washThe combined organic portion washed with brine
9. dry with materialdried over Na2SO4
10. filtrationfiltered
11. concentrationconcentrated in vacuo
12. customto give a light brown oil
13. temperaturecarefully heated to 90° C. with evolution of nitrogen
14. stirringThe mixture was stirred at 90° C. for 2.5 hours
15. temperaturecooled to room temperature
16. customThe solution was quenched with saturated NaHCO3 solution
17. concentrationconcentrated
18. extractionThe oily mixture was extracted with EtOAc (3×)
19. washthe combined organic portion washed with brine
20. dry with materialdried over MgSO4
21. filtrationfiltered
22. concentrationconcentrated in vacuo
23. customThe residue was purified by on silica gel (4:1 hexanes:EtOAc)