A solution of BF3.OEt2 (5.0 ml, 39.8 mmol) in MeCN (90 ml) was added dropwise to a cooled (0°) solution of 3 (13.4 g, 18.3 mmol) and Et3SiH (14.5 ml, 91.5 mmol) in dry CH2Cl2 (150 ml). After 10 min., a sat. aq. solution of NaHCO3 (100 ml) and H2O (200 ml) were added. The mixture was shaken vigorously, the aq. layer was extracted with CH2Cl2, the combined organic layers were extracted with brine, dried (MgSO4), and evaporated. FC (400 g SiO2, EtOAc/hexane 1:5→EtOAc/hexane 1:1) affored 8.35 g (93%) of 4. Rf (EtOAc/hexane 1:2) 0.20.
