OC(C(F)(F)F)=O.[NH2:8][CH2:9][C:10]1[NH:11][CH:12]=[CH:13][C:14]=1[C:15]([OH:17])=O.C(Cl)Cl.CCN(C(C)C)C(C)C.F[P-](F)(F)(F)(F)F.N1(O[P+](N2CCCC2)(N2CCCC2)N2CCCC2)C2C=CC=CC=2N=N1>CCOC(C)=O>[NH:11]1[CH:12]=[CH:13][C:14]2[C:15](=[O:17])[NH:8][CH2:9][C:10]1=2A 5 L round-bottomed flask was charged with 2-(aminomethyl)-1H-pyrrole-3-carboxylic acid TFA salt (1.02 Kg, 2.7 mol), DCM (3.2 L), and DIPEA (2.75 Kg, 21.3 mol). To the reaction mixture was added (benzotriazol-1-yloxy)tripyrrolidinophosphonium hexafluorophosphate (1.55 Kg, 2.97 mol, Accela ChemBio Co. Ltd) and stirred at RT overnight. The solvent was removed in vacuo. The crude material was purified by column chromatography on silica gel (eluting with a gradient of 0% to 5% NH3 (2M in MeOH)/DCM) to give crude product 510 g as sticky oil. The crude product was diluted with EtOAc (4.5 L) and stirred for 1 h. The resulting precipitate was collected by filtration and dried to afford 5,6-dihydropyrrolo[3,4-b]pyrrol-4(1H)-one (104 g, 31% yield) as a white solid. The filtrate was concentrated and re-purified by column chromatography on silica gel to give more product 46.5 g (13.6% yield) as a white solid. Overall 5,6-dihydropyrrolo[3,4-b]pyrrol-4(1H)-one (150.5 g, 44.6% yield) was obtained. MS (ESI, pos. ion) m/z: 123 (M+1); 1H NMR (400 MHz, MeOD) δ 6.87 (d, J=3.2 Hz, 1H), 6.27 (d, J=3.2 Hz, 1H), 4.27 (s, 2H).
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