Phenylselenenic anhydride

The final phase of the synthesis is introduction of the C(9) oxygen by phenylselenenic anhydride (Step H-9) and acetylation. 

The late functionalization included the introduction of the C(10) and C(13) oxygens, which was done by phenylselenenic anhydride oxidation of the enolate in Step 1-5 and by allylic oxidation at C(13) in Step J-l. These oxidative steps are similar to transformations in the Holton and Nicolaou syntheses. 

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