A stirred solution of (2S)-5-oxo-proline tert-butyl ester (T. Kolasa and M. J. Miller, J. Org. Chem., 1990, 55, 1711-1721) (1.13 g, 6.13 mmol) in anhydrous THF (15 mL) was treated at −78° C. with LDA (9.19 mmol) and the reaction was stirred for 15 min. A solution of 2-azidobenzoyl chloride (T. Okawa, T. Sugimori, S. Eguchi and A. Kakehi, Heterocycles, 1998, 47, 1, 375-382) (6.13 mmol) in anhydrous THF (5 mL) was then added dropwise and the reaction mixture was stirred at −78° C. for 1 h before being quenched with saturated aq.NH4Cl. The reaction was allowed to warm to room temperature and the organic layer was washed with saturated aq.NH4Cl, dried (MgSO4), filtered and evaporated to give an oil which was purified by flash chromatography (20% ethyl acetate in hexane) to afford the title compound as a pale yellow oil (1.67 g, 82%): 1H NMR (400 MHz, CDCl3) δ 1.53 (9H, s), 2.14 (1H, m), 2.43 (1H, m), 2.55 (1H, m), 2.69 (1H, m), 4.79 (1H, dd, J 9.2, 3.2 Hz), 7.19-7.22 (2H, m), 7.36 (1H, m), 7.49 (1H, m). 13C NMR (100 MHz, CDCl3) δ 22.1 (CH2), 28.3 (CH3), 31.9 (CH2), 59.3 (CH), 83.0 (C), 118.7 (CH), 125.0 (CH), 127.9 (C), 129.1 (CH), 131.9 (CH), 137.9 (C), 167.5 (C), 170.2 (C), 173.6 (C).
