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Following a modified procedure of Shinkawa et al. and Flader et al.,16,22 the acid 99e (0.291 g, 0.829 mmol) was dissolved in ethyl acetate (10.0 mL) at room temperature, then HNO3 (1.0 mL) and AcOH (6 drops) are added at room temperature. Silver (II) oxide (0.379 g, 3.05 mmol) was then added and the reaction was stirred vigorously at room temperature for 1 hour before being filtered through a pasture pipette and cotton plug, washing the solid with ethyl acetate, and then washing the organic layer with brine. The organic layer was dried over MgSO4, filtered, and condensed. The yellow oil was then purified by either flash column:chromatography (1:1 Et2O:hexanes 0.5% AcOH) or recrystallization from Et2O/hexanes to afford 39a (0.122 g 0.380 mmol, 46%) as a yellow solid.

1. filtrationbefore being filtered through a pasture pipette and cotton plug
2. washwashing the solid with ethyl acetate
3. washwashing the organic layer with brine
4. dry with materialThe organic layer was dried over MgSO4
5. filtrationfiltered
6. customcondensed
7. customThe yellow oil was then purified by either flash column
8. customchromatography (1:1 Et2O:hexanes 0.5% AcOH) or recrystallization from Et2O/hexanes