反应详情

29 mL of boron tribromide (1M in dichloromethane) was added slowly dropwise to a stirred solution of compound 77A from the preceding step (4.5 g, 19 mmol) in 100 mL of dichloromethane under N2 at icebath temperature. An hour after the addition, 60 mL of 15% aq NH4Cl was added slowly dropwise, the mixture was stirred for an additional 30 min, then the layers allowed to separate. The organic layer was washed with water, then sat brine, then dried over MgSO4. The solvent was removed in vacuo, and the residue was chromatographed on a silica gel column in CHCl3/EtOAc (9:1) to afford a clear, amber oil. Crystallization began after several hours under vacuum. The product was recrystallized from 55–60 mL of chloroform/hexanes (1:1). After filtration to remove the first crop of regio-isomeric material, the mother liquor was stripped of solvent in vacuo, and the residue recrystallized from chloroform to yield 0.14 g (3% yield) of the title compound as a white powder, mp 147–148° C., of sufficient purity for use in the next step.

1. additionwas added slowly dropwise
2. customto separate
3. washThe organic layer was washed with water
4. dry with materialdried over MgSO4
5. customThe solvent was removed in vacuo
6. customthe residue was chromatographed on a silica gel column in CHCl3/EtOAc (9:1)
7. customto afford a clear, amber oil
8. customCrystallization
9. waitbegan after several hours under vacuum
10. customThe product was recrystallized from 55–60 mL of chloroform/hexanes (1:1)
11. filtrationAfter filtration
12. customto remove the first crop of regio-isomeric material
13. customthe residue recrystallized from chloroform