Silyl ethers Jones reagent

The sisyl ether is stable to Grignard and Wittig reagents, oxidation with Jones reagent, KF/18-crown-6, CsF, and strongly acidic conditions (TsOH, HCl) that cleave most other silyl groups. It is not stable to alkyllithiums or LiAlH4. 

The main applications of oxidation with chromium trioxide are transformations of primary alcohols into aldehydes [184, 537, 538, 543, 570, 571, 572, 573] or, rarely, into carboxylic acids [184, 574], and of secondary alcohols into ketones [406, 536, 542, 543, 575, 576, 577, 578, 579, 580, 581, 582, 583, 584]. Jones reagent is especially successful for such oxidations. It is prepared by diluting with water a solution of 267 g of chromium trioxide in a mixture of 230 mL of concentrated sulfuric acid and 400 mL of water to 1 L to form an 8 N CrOj solution [565, 572, 579, 581, 585, 556]. Other oxidations with chromic oxide include the cleavage of carbon-carbon bonds to give carbonyl compounds or carboxylic acids [482, 566, 567, 569, 580, 587, 555], the conversion of sulfides into sulfoxides [541] and sulfones [559], and the transformation of alkyl silyl ethers into ketones or carboxylic acids [590]. 

Mild acid then cleaves off the silyl protecting group. The alcohol at position 17 is then oxidized with Jones reagent (chromium trioxide in acetone) to afford 14a-hydroxyestrone 3-methyl ether (32-5). 

Cyclic enones, lactones, and lactams have also been used often as dienophiles in Diels-Alder reactions with (1), again giving mainly the endo adduct, e.g. (12) reacted with (1) to give (13) as the major product in 74% yield (eq 3). As mentioned earlier, the initial adducts are often oxidized (either directly or after hydrolysis of the silyl ether) with Jones reagent to the corresponding enone, e.g. (14) to give (15) (eq 4). This corresponds to the annulation of a cyclohexenone unit onto an existing enone or unsaturated lactone unit and has been used often in synthesis, e.g. in... 

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