To a solution of Intermediate 6 (1.8 g, 6.1 mmol) in acetic acid (40 ml) was added Intermediate 13 (4.0 g, 14.7 mmol) as a crude reaction mixture in 1,2-dimethoxyethane (40 mL). The reaction mixture was allowed to stir for 5 minutes at room temperature and then heated at 80° C. for 1 h. The reaction was cooled to room temperature, poured carefully over saturated aqueous sodium bicarbonate solution (200 mL), and the aqueous layer was made basic to pH˜8 by the addition of solid sodium bicarbonate. The solution was extracted with ethyl acetate (200 mL) and the organic layer was dried over sodium sulfate, filtered and concentrated. The crude product was purified by silica gel chromatography (0-60% EtOAc/hexanes) to afford 13-1 as an oil. MS: m/z=504.4 (M+H).
