Sodium Carbonate → tert-Butyl 3-[4-(ethoxycarbonyl)phenyl]-2,5-dihydro-1H-pyrrole-1-carboxylate

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Reaction Steps

To a cooled (−78° C.) solution of 1-Boc-3-pyrollidinone (8.00 grams, 43.2 mmol) in anhydrous THF (70 mL) was added lithium bis(trimethylsilyl)amide (49.7 mL, 1.0 M in THF, 49.7 mmol) dropwise. After 45 min, a solution of 2-[N,N-bis(trifluoromethylsulfonyl)amino]5-chloropyridine (17.81 g, 45.4 mmol) in THF (65 mL) was added, and the resulting mixture was allowed to warm slowly to ambient temperature overnight, at which point it was quenched by pouring into brine. The mixture was extracted with EtOAc. The organic phase was separated, dried over anhydrous sodium sulfate, and concentrated in vacuo. The resulting enol triflate was filtered though silica gel, concentrated in vacuo, and used without further purification. To a flask containing the enol triflate obtained above (4.94 g, 15.6 mmol) were added 4-ethoxycarbonylphenylboronic acid (3.32 g, 17.1 mmol) and trans-dichlorobis(triphenylphosphine) palladium (II) (1.09 g, 1.56 mmol). Acetonitrile (78 mL) and sodium carbonate (39 mL, 1.0 M aqueous, 39 mmol) were added, and the resulting mixture was degassed via nitrogen sparge. The reaction mixture was stirred at 70° C. for 3 h, then was allowed to cool to room temperature and was poured into water. The mixture was extracted with EtOAc, and the organic phase was concentrated in vacuo. Purification by chromatography on silica gel (0 to 25% EtOAc in hexanes, then 25 to 100% EtOAc in hexanes) provided the title compound: LCMS m/z 261.9 [M-t-Boc]+; 1H NMR (500 MHz, CDCl3) δ 8.03 (d, J=8.0 Hz, 2 H), 7.44 (d, J=8.5 Hz, 2H), 6.29 (ddd, J=25.0, 4, 4 Hz, 1H), 4.58-4.46 (m, 2H), 4.41-4.28 (m, 2H), 4.38 (q, J=7.0 Hz, 2H), 1.53 and 1.51 (s, doubled (rotamers) 9H), 1.40 (t, doubled (rotamers) J=7.0 Hz, 1.5H), 1.39 (t, doubled (rotamers) J=7.0 Hz, 1.5H).

Provenance & Evidence