Potassium vinyltrifluoroborate (0.913 g, 6.82 mmol), TEA (0.950 mL, 6.82 mmol), and PdCl2(dppf)-CH2Cl2 adduct (0.186 g, 0.227 mmol) were added to a solution of the product from step 2 (2.26 g, 4.54 mmol) in EtOH (45.4 mL). The mixture was then heated to reflux for 1 h. The EtOH was removed in vacuo, and the residue was taken up in EtOAc and extracted with water. The organic layer 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 (99%) of the title compound. LRMS ESI+ ((M-Boc)+H)+345.3.
