[CH3:1][O:2][C:3]([C:5]1[NH:9][CH:8]=[C:7]([CH2:10][CH2:11][C:12]([OH:14])=O)[CH:6]=1)=[O:4].ClCCCl.C(=O)(O)[O-].[Na+]>O>[O:14]=[C:12]1[C:8]2[NH:9][C:5]([C:3]([O:2][CH3:1])=[O:4])=[CH:6][C:7]=2[CH2:10][CH2:11]1To a polyphosphoric acid (115%, 1.6 g) was added 3-(5-(methoxycarbonyl)-1H-pyrrol-3-yl)propanoic acid (174 mg, 0.88 mmol) and 1,2-dichloroethane (8 mL). The reaction mixture was heated for 1 h at 100° C. Water (20 mL) was added and the mixture was carefully poured into a 50 mL Erlenmeyer flask containing solid sodium bicarbonate and ice. The reaction was neutralized (pH 7) and was then extracted with EtOAc (5×50 mL). The combined organic extracts were washed with water, NaHCO3 and brine, dried (Na2SO4) filtered and concentrated. Purification by flash chromatography (0-40% EtOAc/Heptane) afforded methyl 6-oxo-1,4,5,6-tetrahydrocyclopenta[b]pyrrole-2-carboxylate (106 mg, 67%). 1H NMR (400 MHz, CHLOROFORM-d) δ ppm 2.91 (s, 4H), 3.92 (s, 3H), 6.78 (d, J=1.76 Hz, 1H), 9.33 (br s, 1H); LCMS-MS (ESI+) 180.2 (M+H).
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