To a solution of the product from Step 2 (2.26 g, 4.54 mmol) in EtOH (45.4 mL) was added potassium vinyltrifluoroborate (0.913 g, 6.82 mmol), Et3N (0.950 mL, 6.82 mmol), and PdCl2(dppf)-DCM adduct (0.186 g, 0.227 mmol). The reaction mixture was then heated to reflux for 1 hour, cooled to RT; the volatiles were evaporated in vacuo; and the residue partitioned between EtOAc and water. The organic phase was dried over MgSO4, and the solvent was removed in vacuo. The crude material was purified on silica (gradient elution, 0-5% MeOH/DCM) to yield 2.0 g of the title compound. LRMS ESI+ ((M-Boc)+H)+ 345.3.
