3.3.9. 1-Tosyl-1,3,4,5-tetrahydropyrrolo[4,3,2-de]quinoline-7,8-dione (Ts-damirone C, 19)

TFA (11.5 mL, 150 mmol, 50 equiv.) was added to a solution of 18 (1.34 g, 3.00 mmol) in CH₂Cl₂ (50 mL) over 10 min at 0 °C, and the mixture was stirred for 70 min. The reaction mixture was concentrated in vacuo, and the resulting red-brown oil was redissolved in MeOH (60 mL). Et₃N (4.16 mL, 30 mmol, 10.0 equiv.) was added to a solution over 10 min at 0 °C, and the mixture was stirred for 20 min. The reaction mixture was concentrated in vacuo, and the residue was diluted with CH₂Cl₂ and H₂O. The layers were separated, and the aqueous layer was reextracted with CH₂Cl₂ twice. The combined organic layer was washed, saturated NaHCO₃ aq., and the aqueous layer was reextracted with CH₂Cl₂. The organic layer was dried over Na₂SO₄ and was concentrated in vacuo. The crude was purified by silica gel column chromatography (CH₂Cl₂/MeOH = 10:1) to give 19 (0.57 g, 55%) as a purple solid.

The spectroscopic and physical data were identical to those reported [25].