To a refluxing solution of the compound from Step D (45.5 g, 122 mmol) and AIBN (1.0 g) in CCl4 (2.5 L) was added a mixture of NBS (23.0 g, 129 mmol) and AIBN (1.0 g) in ten equal portions. The reaction mixture was refluxed for 2 h after the addition of the last portion of NBS/AIBN. The reaction mixture was concentrated to approximately 1 L and washed 3 times with water (1 L). The organic layer was dried with anhydrous Na2SO4, filtered and the solvent removed. Toluene (200 ml) was added to the residue and then evaporated. Repeating this procedure gave 48 g of the title compound that was used without further purification.
