[CH3:1][C:2]1[CH:7]=[C:6]([CH2:8][CH2:9][C:10]2[CH:15]=[CH:14][CH:13]=[CH:12][CH:11]=2)[CH:5]=[C:4]([CH3:16])[N:3]=1.[N+:17]([O-])([OH:19])=[O:18].[N+]([O-])([O-])=O.S(=O)(=O)(O)O.C(=O)([O-])O.[Na+]>C1COCC1.C(OCC)C>[CH3:1][C:2]1[CH:7]=[C:6]([CH2:8][CH2:9][C:10]2[CH:15]=[CH:14][C:13]([N+:17]([O-:19])=[O:18])=[CH:12][CH:11]=2)[CH:5]=[C:4]([CH3:16])[N:3]=1
Compound (2) (20 g, 88.9 mmols) was dissolved in THF (150 ml), and nitric acid (6.7 ml, 60% aq. solution, 1 eq) was added. Diethylether was added to the clear solution until it remained turbid, and the mixture was left in the freezer for crystallization. The white crystals of nitrate (quantit. yield) were added in small portions to well-chilled sulfuric acid (150 ml), never allowing the temperature to reach 10° C., whereafter the mixture was warmed at 50° C. for 10 min. The resulting brown solution was poured onto ice and neutralized with solid sodium hydrogen carbonate. The organic material was extracted with chloroform (3×200 ml), and after drying over sodium sulphate, the chloroform extract was flash chromatographed using 4% ethanol/chloroform as a solvent. The appropriate fractions were collected and evaporated yielding a pure yellow solid
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