[N:1]1[C:5]2[CH:6]=[CH:7][CH:8]=[CH:9][C:4]=2[NH:3][C:2]=1[CH2:10][O:11][C:12]1[CH:17]=[CH:16][CH:15]=[C:14]([O:18][CH3:19])[CH:13]=1.C([O-])([O-])=O.[K+].[K+].Br[CH2:27][C:28]([CH3:30])=[CH2:29]>CC#N>[CH3:29][C:28](=[CH2:27])[CH2:30][N:1]1[C:5]2[CH:6]=[CH:7][CH:8]=[CH:9][C:4]=2[N:3]=[C:2]1[CH2:10][O:11][C:12]1[CH:17]=[CH:16][CH:15]=[C:14]([O:18][CH3:19])[CH:13]=1To a solution of 51 (16.51 g, 0.065 mol) in CH3CN (150 mL) was added K2CO3 (17.94 g, 0.13 mol) followed by addition of 3-bromo-2-methylpropene (8.78 g, 0.065 mol) under Ar. The resulting mixture was stirred at rt overnight. The reaction mixture was filtered, and the filter cake was washed with CH3CN (100 mL). The filtrate was concentrated in vacuo to give an oil. The oil was chromatographed on 150 g of silica gel with 30 g of anhydrous Na2SO4 on top packed with hexanes. The column was eluted with 150 mL portions of 10% EtOAc in hexanes for fractions 1-5, 20% EtOAc in hexanes for fractions 6-14 and 25% EtOAc for fraction 15-16. The product was eluted in fractions 7-16 (TLC solvent: 50% EtOAc in hexanes) to give 19 g (95%) of Compound #3 as a viscous oil. HPLC analysis showed a purity of 99%. 1H NMR for HCl salt (300 MHz, CD3OD): δ 7.9 (m, 2H), 7.7 (m, 2H), 7.3 (t, 1H), 6.65-6.8 (m, 3H), 5.7 (s, 2H), 5.2 (s, 2H), 5.1 (s, 1H), 4.9 (s, 1H), 4.7 (s, 1H), 3.8 (s, 3H), 1.85 (s, 3H).
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