To a solution of 2-(7-Amino-thianthren-1-yl)-6-morpholin-4-yl-pyran-4-one (21) (575 mg, 1.4 mmol) was suspended in ethanol (5 mL) was added tetrafluoroboric acid (54 wt % in ether, 3 ml, 1.68 mmol). The mixture was stirred at room temperature for 10 minutes before being cooled to 0° C. Butyl nitrite (220 μl, 2.8 mmol) was then added dropwise and the mixture stirred for 30 minutes before the addition of diethyl ether (40 ml) which caused a precipitate to form. The solid was collected by filtration and washed with cold diethylether (30 ml) then added to a solution of cupric nitrate trihidrate (210 g, 870 mmol) and cuprous oxide (190 mg, 1.31 mmol) in water (300 ml). The reaction was stirred for 12 hours and then filtered. The filtrant was washed with water, dried in a desiccator and used without further purification give the title compound (0.58 g, 100%). NMR (300 MHz, CDCl3): δH=10.08 (1H, bs); 7.76 (1H, dd); 7.60 (1H, dd); 7.46 (1H, dd); 7.35 (1H, dd); 7.02 (1H, d); 6.74 (1H, dd); 6.24 (1H, d); 5.55 (1H, d); 3.69 (H, m), 3.36 (4H, m); m/z (LC-MS, ESP), RT=3.83 min, (M++1)=412
