To 32 mL of acetic acid was added compound 13-5 (2.34, 6.4 mmol) resulting in a suspension. In a separate flask KMnO4 (2.48 g, 15.7 mmol) was dissolved in 40 mL of H2O. The KMnO4 solution was then added to the solution of compound 13-5 in acetic acid and allowed to stir for 2 h at ambient temperature. The dark reaction mixture was diluted with EtOAc (200 mL) and washed three times with 150 mL portions of brine. The combined organic layers were dried over MgSO4, then filtered and concentrated in vacuo to give title compound 13-6 as a pale yellow solid.
