[Cl-].[Al+3].[Cl-].[Cl-].[C:5](OC(=O)C)(=[O:7])[CH3:6].[CH2:12]([O:14][C:15]([C:17]1[NH:18][C:19]([CH3:23])=[C:20]([CH3:22])[CH:21]=1)=[O:16])[CH3:13]>ClC(Cl)C>[CH2:12]([O:14][C:15]([C:17]1[NH:18][C:19]([CH3:23])=[C:20]([CH3:22])[C:21]=1[C:5](=[O:7])[CH3:6])=[O:16])[CH3:13]To a solution of aluminum chloride (50.19 g, 0.376 mol) in dry dichloroethane (580 mL) at 25° C. was added slowly acetic anhydride (17.75 mL, 0.188 mol). The resulting mixture was stirred at room temp. for 10 minutes, then a solution of pyrrole 33 (10.49 g, 0.0627 mol) in dichloroethane (30 mL) was added and the reaction mixture was stirred at room temp. for 2 h. After an additional 3 h at 80° C., the mixture was poured into ice water and extracted with dichloromethane. The organic layer was dried with anhy. sodium sulfate and concentrated in vacuo to an orange residue. Short plug filtration over silica gel (30% ethyl acetate/70% hexanes) gave 7.5 g (60%) of ethyl-3-acetyl-4,5-dimethyl-2-pyrrole carboxylate 34. 1H NMR (CDCl3) δ 9.0 (bs, 1H), 4.3 (q, 2H), 2.7 (s, 3H), 2.1 (s, 3H), 1.9 (s, 3H), 1.3 (t, 3H) ppm.
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