[N+:1]([CH2:4][CH2:5][C:6]1[NH:7][CH:8]=[CH:9][CH:10]=1)([O-:3])=[O:2].[O:11]=[C:12]([CH:14]=[C:15]([CH3:17])[CH3:16])[CH3:13].[CH2:18]1[CH2:28][CH2:27]N2[C:21](=NCCC2)[CH2:20][CH2:19]1.[CH3:29]C#N>C(OCC)(=O)C>[CH3:29][C:21]1[CH:20]=[CH:19][C:18]([C:10]2[CH:9]=[CH:8][NH:7][C:6]=2[CH2:5][CH:4]([N+:1]([O-:3])=[O:2])[C:15]([CH3:17])([CH3:16])[CH2:14][C:12](=[O:11])[CH3:13])=[CH:28][CH:27]=1Following a standard procedure (Ptaszek et al., supra), a mixture of 3 (460 mg, 2.00 mmol) and mesityl oxide (458 μL, 4.00 mmol) in CH3CN (4.0 mL) was treated with DBU (897 μL, 6.00 mmol). The reaction mixture was stirred for 24 h at room temperature, diluted with ethyl acetate (15.0 mL) and washed with water and brine. The organic layer was dried (Na2SO4) and concentrated. Excess mesityl oxide was removed under high vacuum. The resulting oil was chromatographed [ethyl acetate/hexanes (1:2)] to afford a light brown oil (486 mg, 74%): 1H NMR δ 1.08 (s, 3H), 1.19 (s, 3H), 2.10 (s, 3H), 2.37 (s, 3H), 2.37, 2.55 (AB, 2J=17.6 Hz, 2H), 3.21 (ABX, 3J=2.6 Hz, 2J=15.6 Hz, 1H), 3.38 (ABX, 3J=11.6 Hz, 2J=15.6 Hz, 1H), 5.18 (ABX, 3J=2.6 Hz, 3J=11.6 Hz, 1H), 6.22-6.24 (m, 1H), 6.67-6.69 (m, 1H), 7.20 (d, J=8.0 Hz, 2H), 7.24 (d, J=8.0 Hz, 2H), 8.05-8.20 (br, 1H).
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