L-Pyroglutamic Acid → tert-Butyl 5-oxo-L-prolinate

Participants

Reaction Steps

Perchloric acid (70% aqueous, 0.521 cm3, 6.05 mmol) was added dropwise to a stirred suspension of (S)-pyroglutamic acid 9 (1 g, 7.75 mmol) in tert-butyl acetate (12 cm3, 85.5 mmol). The mixture was stirred for 24 h then sodium carbonate (0.80 g, 7.60 mmol) was added cautiously, ether was added and the organic phase washed with saturated sodium hydrogen carbonate solution and brine. The aqueous phase was extracted with ethyl acetate, dried (MgSO4), filtered and the solvent removed to yield an oil to which was added carbon tetrachloride and the solvent evaporated in vacuo to remove traces of acetic acid to give ester 10 (0.81 g, 56%) as a white solid: δH (300 MHz; CDCl3; Me4Si) 1.48 [9H, s, C(CH3)], 2.33-2.45 (4H, m, 3-H2, 4-H2), 4.12-4.16 (1H, m, 5-H) and 6.16 (1H, br s, N—H); δC (75 MHz; CDCl3) 24.7 (CH2, 4-C), 27.8 [CH3, C(CH3)], 29.2 (CH2, 3-C), 55.9 (CH, 5-C), 82.3 [quat., C(CH3)], 170.9 (quat., 5-CO) and 177.7 (quat., 2-C).

Provenance & Evidence