A mixture of 1-[[2-(diethylamino)ethyl]amino]-9-oxothioxanthen-4-carboxaldehyde (3.40 g, 9.59 mmol), formanilide (31g) and formic acid (3 mL) were heated to 160° C. for 2 hours. The mixture was cooled, poured into water (200 mL) and extracted with ether (3×150 mL). The aqueous layer was basified with 5N NaOH, extracted with CHCl3 (3×150 mL) and the combined organic extracts were dried over Na2SO4 and filtered through florisil eluting with CHCl3 (100%), then 5% isopropylamine/CHCl3. The solvent was removed in vacuo and the residue was purified by column chromatography on silica eluting with 0.5% to 1% isopropylamine/CHCl3 and then by recrystallization from benzene/hexane (2x) to afford 1.88 g of the desired product.
