A solution of intermediate D8 (0.65 g, 1.91 mmol) and N-chlorosuccinimide (0.25 g, 1.91 mmol) in DMF (10 ml) was stirred at 45° C. for 16 hours. After cooling to room temperature water was added and the solution was extracted with EtOAc, The organic layer was separated and washed with brine, dried (Na2SO4) and the solvent evaporated in vacuo. The crude product was purified by column chromatography (silica gel; DCM/EtOAc 8:2 as eluent). The desired fractions were collected and evaporated in vacuo to yield E1 (0.20 g, 28%) as a pale pink solid.
