To a solution of 9-hydroxy-4-phenylpyrrolo[3,4-c]carbazole-1,3(2H,6H)-dione (I; Ar=phenyl) (0.50 g, 1.52 mmol) in pyridine (30 mL) under nitrogen was added phosphorous oxychloride (140 □L, 1.52 mmol) dropwise. After 40 minutes stirring at room temperature a further portion of phosphorous oxychloride (40 □L) was added and then after another 20 minutes, benzyl alcohol (0.66 mL, 6.38 mmol) was added. After 3 hours the reaction mixture was diluted with 1N hydrochloric acid and extraction with ethyl acetate. The organic phase was dried, the drying agent was removed and the solution was concentrated to dryness, before being chromatographed on silica eluting with methanol/dichloromethane (3:97) to give the dibenzyl phosphate (336) (284 mg, 32%) as a pale yellow powder, mp 193–194° C. 1H NMR δ [(CD3)2SO] 12.12 (br s, 1H), 11.15 (br s, 1H), 8.81 (br s, 1H), 7.69 (s, 1H), 7.63 (m, 3H), 7.48–7.34 (m, 14H), 5.22 (d, JH-F=8.3 Hz, 4H). Found: C, 69.65; H, 4.37; N, 4.88; P, 5.26. C34H25N2O6P requires: C, 69.38; H, 4.28; N, 4.76; P, 5.26.
