In toluene (12 mL) was dissolved ethyl 7-benzoyl-5,10-dihydro-5-(3-methyl-2-butenyl)-1-phenazinecarboxylate (1.26 g, 2.95 mmol.) obtained in Example 2. To the mixture were further added 3-(dimethylamino)-1-propanol (3.50 mL, 29.5 mmol.) and tetra-n-butyl-1-isothiocyanate-3-hydroxydistannoxane (SCN(n-Bu)2SnOSn(n-Bu)2OH; 329 mg, 0.591 mmol.). The mixture was stirred at 100° C. for 24 hours in the stream of gaseous nitrogen. The mixture was further stirred at 100° C. for 24 hours, after addition of 3-(dimethylamino)-1-propanol (1.50 mL) and the above-mentioned tin compound (329 mg, 0.591 mmol.). The reaction mixture was cooled to room temperature and poured into saturated aqueous sodium hydrogencarbonate solution. The aqueous mixture was then extracted with ethyl acetate. The extract was washed with two portions of saturated aqueous sodium chloride solution and dried over anhydrous sodium sulfate. The dried extract was placed under reduced pressure to distill the solvent off. The residue was purified by medium pressure column chromatography (CHCl3 /methanol=1/0→95/5), to give the desired compound (142 mg, 10%).
