Triketone hydroxylation

In order to activate the 21 position to halogenation, it is hrst converted to an oxalate. Condensation of the triketone with ethyl oxalate in the presence of alkoxide proceeds preferentially at the 21 position to give (12-2) due to the well-known enhanced reactivity of methyl ketones. Reaction of the crude sodium enolate with bromine leads to the dibromide (12-3), the oxalate moiety being cleaved under the reaction conditions. The Favorskii rearrangement is then used to, in effect, oxidize the 17 position so as to provide a site for the future hydroxyl group. Thus, treatment of (12-3) with an excess of sodium methoxide hrst provides an anion at the 17 position (12-4). This then cyclizes to the transient cyclopropanone (12-5)... 

Reaction of that triketone with ethylene glycol selectively forms the expected 3,20-bisacetal the still free remaining ketone at Cn is next reduced with lithium aluminum hydride to yield the expected /8-hydroxyl group (11-1) (Scheme 7.11). Acid hydrolysis of the acetal groups followed by reaction with selenium dioxide generates the... 

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