A solution of the product of Step B (8.58 g, 18.74 mmol, 1 eq), phthalic anhydride (5.55 g, 37.5 mmol, 2 eq) and DIEA (11.3 mL, 55.6 mmol, 3.5 eq) in chloroform (150 mL) was heated to 70° C. for 2 hours. The solution was cooled to rt and carbonyl diimidazole (2.24 g 13.82 mmol, 3 eq) was added and the solution heated to 60° C. for 2 hours. The solution was cooled to rt, 1 N HCl was added, the aqueous extracted with DCM, the organics combined, dried over MgSO4 and concentrated. Purification by chromatography (200 g column) eluting with 30 to 60 to 80% EA/heptane afforded the product of Step C. Calculated for C24H21F3N2O5: 474.1 (M+1). found: 475.1.
