Diketones from diol

Diketones from diols s. 16, 871 Chromium trioxide I pyridine Oxo compounds from alcohols... 

An example of the construction of a 1,2-diketone from a 1,2-diol comes from the total synthesis of ( )-cephalotaxine (54) where the Corey-Kim conditions were used to convert diol 52 to diketone 53 in 89% yield while other oxidation methods were reported to have failed to affect this conversion.15 The more accessible ketone was then converted to the enol ether and LAH reduction afforded the racemic natural product 54. 

Equally smooth is the reduction of aliphatic, alicyclic, and aromatic diketones to diols by the equivalent amount of complex boron hydrides. For instance, excellent yields of, mainly, m so-diols are obtained from acyclic 1,3-diols.389 The preparation of /ra .s-5-hydroxy-4a-methyl-zl1 8a-octalin-2-one from the corresponding dione by NaBN4390 is an example of selective reduction of one keto group of a dione ... 

TLC is commonly used for the separation of different classes of wax components or for analysis of monomers from cutin and suberin depolymerization. A typical separation is shown in Fig. 6.12. By such methods, it is possible to separate hydrocarbons, wax esters, primary alcohols, secondary alcohols and /8-diketones from plant waxes (von Wettstein-Knowles, 1979). Products of hydrogenolysis from cutin can be separated by TLC into alkan-l-ols, alkane-a,ft>-diols, Cis triols, Ci6 triols and Cis tetrols (Kolattukudy, 1980). Unsaturated components can be resolved by argentation-TLC (Tulloch, 1976) and threo or erythro diastereoisomers separated by boric acid/silica gel TLC (Eglinton and Hunneman, 1968). Straight-chain compounds can be preferentially removed from branched compounds as their urea complexes (Kolattukudy, 1980). 

Diketones from hydroxy-a,j -ethyleneketones via diols—Robinson hydro-phenanthrene ring synthesis s. 16, 871... 

Titanium chelates are formed from tetraalkyl titanates or haUdes and bi- or polydentate ligands. One of the functional groups is usually alcohoHc or enoHc hydroxyl, which interchanges with an alkoxy group, RO, on titanium to Hberate ROH. If the second function is hydroxyl or carboxyl, it may react similarly. Diols and polyols, a-hydroxycarboxyflc acids and oxaUc acid are all examples of this type. P-Keto esters, P-diketones, and alkanolamines are also excellent chelating ligands for titanium. 

Selective hydroxylation with osmium tetroxide (one equivalent in ether-pyridine at 0 ) converts (27) to a solid mixture of stereoisomeric diols (28a) which can be converted to the corresponding secondary monotoluene-sulfonate (28b) by treatment with /7-toluenesulfonyl chloride in methylene dichloride-pyridine and then by pinacol rearrangement in tetrahydrofuran-lithium perchlorate -calcium carbonate into the unconjugated cyclohepte-none (29) in 41-48 % over-all yield from (27). Mild acid-catalyzed hydrolysis of the ketal-ketone (29) removes the ketal more drastic conditions by heating at 100° in 2 hydrochloric acid for 24 hr gives the conjugated diketone (30). 

Since 1,5-enediones are usually obtained via pyrylium salts, syntheses of the type found in Section B, 2, a have a rather theroetical interest, save for a few special syntheses. There exist several direct syntheses of l,5-enediones, e.g., from j8-chlorovinyl ketones and j8-diketones or j8-keto esters special pathways to 1,5-enediones have also been described, namely, oxidation with lead tetraacetate or with periodic acid of cyclopentene-l,2-diols. ... 

In a recent total synthesis of the novel neurotrophic agent merrilactone A (22, Scheme 4) by Inoue and Hirama [24], key intermediate 21 with the cis-bicyclo[3.3.0] octane framework embedded within the caged pentacycle 22 was elaborated from cyclobutane 18 by a sequence of RCM and immediate cleavage of the resulting bicyclic vicinal diol 19 to raeso-diketone 20. Cyclooctenedione 20 then underwent regioselective transannular aldol reaction at low temperature (LHMDS, THF, -100 °C) to produce a 3 1 mixture of isomers in 85% combined yield. The major isomer 21 with the required stereochemistry was then converted into the racemic natural compound ( )-22 in 19 steps. 

The monoketone bis(2,2, /V,/V -bipyridyl)ketone forms a [CoinL2]+ complex on reaction with [Co(NH3)4(C03)]+ in water.981 As reported for a quite different Co11 complex, the ketone is hydrated to form the gem diol which binds as a monodeprotonated O-donor along with the two pyridine groups in a tridentate chelate, with very little distortion from octahedral observed in the complex. This appears to represent a facile route for this type of inherently poor donor to achieve coordination. Chelated /3-diketonate anions are long-studied examples of O-donor chelates, and continue to be examined. A simple example is the m-[Co(acac)2(NH 3)2]1 (acac = 2,4-pentane-dionate), structurally characterized and utilized to produce molecular mechanics force field parameters for /3-diketones bound to Co111.982... 

Ring A diosterols.3 The ring A diosterols (3 and 4) of triterpenes can be prepared from the A2-alkene (1) by osmylation to form the two possible cis-diols (2), which on Swern oxidation give the a-diketone (3). The same diketone is also obtained by Swern oxidation of the 2(3,3a-diol, the product of peracid oxidation followed by acid cleavage. The diketone 3 rearranges to the more stable diosphenol (4) in the presence of base. 

Scheme 20 Selectivity of unsymmetrical 1,2-diketone formation from unsymmetrical diesters of 1,n-diols.

TA NaBr-MRNi has been found to be an effective catalyst for enantio-differentiating hydrogenations of ketones which have a general structure of R—CO—CH2—X—O— as shown in Table XVII (52c) and methyl ketones as shown in Table XXVI (52d). Among all, /i-diketones and /i-ketoesters are the most favorable substrate for this catalyst. Specific rotations [a] 0 of (R, R )-diols produced from /3-diketones by hydrogenation with this catalyst are summarized in Table XXVII (44). 

A 2,2-disubstituted chromanone results from the condensation of o-hydroxyacetophenone with diethyl oxalate. The initially formed 1,3-diketone cyclizes spontaneously to ethyl 2-hydroxy-4-oxochroman-2-carboxylate (77LA1707). The enolate also reacts with aliphatic ketones to give 2,2-disubstituted chroman-4-ones via the diol (79TL3685). 

Nitrogen-coordinated pentacoordinate complexes have been used as stereoselective reducing agents in the preparation of erythro-(meso)- 1,2-diols from diketones and a-hydroxyketones109. The reducing agent was the (l-naphthylamino-8)trihydridosilane 92e. After formation of the dioxo chelate from the diketone (equation 32), the diol was obtained from the pentacoordinate silicon complex by reduction with LiAlILt. 29 Si NMR spectroscopy was used for the product-ratio analysis in this reaction, which was found to yield primarily the erythro diols. 

---