[CH3:1][O:2][C:3](=[O:16])[C:4]([NH:8][C:9]([O:11][C:12]([CH3:15])([CH3:14])[CH3:13])=[O:10])([CH3:7])[CH2:5][OH:6].CO[C:19](OC)([CH3:21])[CH3:20].B(F)(F)F.O(CC)CC>CC(C)=O>[CH3:1][O:2][C:3]([C:4]1([CH3:7])[CH2:5][O:6][C:19]([CH3:21])([CH3:20])[N:8]1[C:9]([O:11][C:12]([CH3:15])([CH3:14])[CH3:13])=[O:10])=[O:16]To a stirring solution of 3 (9.342 g, 40 mmol) in acetone (115 mL) in a flame dried round bottom flask under an inert atmosphere was added 2,2-dimethoxypropane (66 mL). To this solution was added BF3-OEt2 (0.30 mL, cat) and stirring was continued at rt for 2 h. The reaction mixture was then concentrated in vacuo to an orange oil which was purified by flash chromatography to provide 4 (9.392 g, 85%) as a white solid. Rf=0.55 (1:3 EtOAc/hexanes). Compound was observed as an uneven mixture of rotomers.
Loading…
