[CH2:1]([N:8]1[C:16]2[C:11](=[CH:12][CH:13]=[CH:14][CH:15]=2)[C:10]([CH2:18][C:19]([N:21]([CH3:23])[CH3:22])=[O:20])(O)[C:9]1=[O:24])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.C(OC(=O)C)(=O)C>[Zn].C(O)(=O)C>[CH2:1]([N:8]1[C:16]2[C:11](=[CH:12][CH:13]=[CH:14][CH:15]=2)[CH:10]([CH2:18][C:19]([N:21]([CH3:23])[CH3:22])=[O:20])[C:9]1=[O:24])[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1A flask is charged with 2-(1-benzyl-3-hydroxy-2-oxo-2,3-dihydro-1H-indol-3-yl)-N,N-dimethyl-acetamide (Example 19) (10.0 g, 30.8 mmol), acetic acid (250 mL), acetic anhydride (100 g), and Zn-dust (20 g). The mixture is kept under reflux, until all of the starting material is consumed (3 h). The solids are then filtered off, and from the filtrate the solvent is removed to leave an oil which crystallizes to a pale brown solid on treatment with di-iso-propyl ether. Yield of the title compound: 9.2 g (96.8%). 1H-NMR (CDCl3, 300 MHz) δ 2.73 (dd, 1, 2J=16.5 Hz, J=9.4 Hz, CH2NMe2); 3.00, 3.01 (2 s, 6, N(CH3)2); 3.20 (dd, 1, J=3.2 Hz, CH2NMe2); 4.06 (dd, 1, H-3); 4.90, 4.97 (AB, 2, 2J=15.6 Hz, CH2N); 6.70 (d, 1, J=7.9 Hz, H-7); 6.97 (“dtr”, J=7.5 Hz, J=1.2 Hz, H-5); 7.13 (“dtr”, J=7.8 Hz, J=1.2 Hz, H-6); 7.22-7.29, 7.29-7.33 (m, 5, 5 Ph-H); 7.38 (br d, 1, J=7.5 Hz, H-4). 13C-NMR (CDCl3, 75 MHz) δ 35.25 (CH2NMe2); 36.07, 37.51 (N(CH3)2); 42.59 (C-3); 44.28 (NCH2Ph); 109.12 (C-7); 122.66 (C-5); 124.85 (C-4); 127.49 (Ph meta-C); 127.71 (Ph para-C); 128.04 (C-6); 128.92 (Ph ortho-C); 129.63 (C-9); 136.19 (Ph ipso-C); 143.52 (C-8); 170.00 (CONMe2); 178.02 (C-2).
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