Conversion to ketones

A 8 A solution of chromic acid is prepared by dissolving 26.72 g of chromium trioxide in a mixture of 23 ml of concentrated sulfuric acid and enough water to make the total volume of the solution 100 ml. Rapid dropwise addition of a slight excess of this reagent to an acetone solution (2 % or less) of the hydroxy steroid at room temperature or below with stirring usually results in complete conversion to ketone in less than 10 min. The product is isolated by dilution with water followed by filtration or extraction. 

On page 94 appeared a problem on the synthesis of acid (1), needed for conversion to ketone (2), The problem under investigation was sterlc hindrance in nucleophilic additions to ketones and a crowded ketone with a chiral centre was needed. 

Conversion to Ketone— and Ketene Zirconocene Complexes and Reactions Thereof 5.3.2.1 Ketone zirconocene complexes... 

Medium-chain fatty acids are also present in bovine milk and some plant oils (e.g. coconut). After digestion of the triacylglycerol, they are taken up by the enterocytes in the small intestine but are not esterified. Instead they pass directly into the hepatic portal blood, from where they are taken up by the liver for complete oxidation or conversion to ketone bodies. 

An intramolecular cycloaddition of the tetradecatrienyl nitroethyl ether 263 was used in the synthesis of the 14-membered bicyclic precursor 265 of crassin acetate 266, a cembrane lactone possessing antibiotic and antineoplastic activity (332). Nitro compound 263 was obtained from farnesyl acetate (262) in several steps and was then treated with phenyl isocyanate and triethylamine to give the tricyclic isoxazoline 264 (Scheme 6.98). Conversion to ketone 265 was accomplished by hydrogenation of the cycloadduct with Raney Ni and boric acid followed by acetylation (332). In this case, the isoxazoline derived from a 3-butenyl nitroethyl ether moiety served to produce a 3-methylenetetrahydropyran moiety (332). 

In the first synthesis [50] phenol (150) prepared from dehydroabietic acid as starting material [51] and this was converted to trifluoroacetate (151). The azide (152) prepared from (151), underwent Curtis rearrangement yielding isocyanate (153). Reduction of (153) followed by heating the resulting material with formic acid and formaldehyde provided the tertiary amine (154). Its conversion to ketone (155) was accomplished in three steps (a) oxidation with m-cloroperbenzoic acid, (b) Cope elimination and (c) oxidative cleavage. 

Cyclopropanols are thermally unstable. Accordingly, thermal conversion to ketones is synthetically equivalent to hydrolysis. For example, heating cyclopropanol 22 to 160-170°C provides ketone 23 in 85% yield. 

Concerning reactions of 1,2,6-thiadiazines with oxidants, reaction of 3,5-diaminothiadiazine Ila with chromium trioxide in acetic acid resulted in smooth conversion to ketone 44 in high yield. Compound Ila with selenium dioxide afforded 4,4 -bisthiadiazine 45, which by oxidation with chromium trioxide yielded ketone 44 (77JHC431) (Scheme 5). 

The fact that the resultant methylenecyclopentanc can be readily manipulated into the unsubstituted cyclopentene present in the target, highlights the synthetic versatility of the methylene functionality in the cycloaddition products. Alternative manipulations would be conversion to ketone by ozonolysis or to an alkyl-substituted system. 

Because Di Abietes produces very little insulin, she is prone to developing ketoacidosis. When insulin levels are low, HSL of adipose tissue is very active, resulting in increased lipolysis. The fatty acids that are released travel to the liver, where they are converted to the triacylglycerols of VLDL. They also undergo p-oxidation and conversion to ketone bodies. If Di does not take exogenous insulin or if her insulin levels decrease abruptly for some physiologic reason, she may develop a ketoacidosis (DKA). In fact, she has had repeated bouts of DKA. 

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