Isomeric ketones

In cyclic ketones, the diradical intermediates can recombine, leading to isomerized ketones ... 

The first, and to this writing still only case of a ketone a-cleavage-recombi-nation sequence in the steroid field was reported by Butenandt, who found that 17-ketones epimerize at C-13. Ultraviolet irradiation of either stereoisomer produces an equilibrium mixture in which the thermodynamically more favored 13a-compound cf. (15)] with cw-fusion of rings C and D predominates at room temperature. As ultraviolet absorption energies and intensities of the two isomeric ketones are practically identical, the equilibrium composition depends largely on the rate of the competing recombination process from (14). For further examples of the photoisomerization at C-13 of 17-ketosteroids, see ref. 8, 12, 15 and 43. 

At the same time, the hydration of 3(5)-phenyl-5(3)-phenylethynylpyrazole 45 in sulfuric acid in the presence of mercury acetate leads to the formation of two isomeric ketones 46 (yield 44%) and 47 (yield 3%) (68LA117) (Scheme 88). 

If pseudo-ionone be heated with dilute sulphuric acid and a little glycerine, it is converted into another isomeric ketone, and now well-known ionone, CjgHo O. 

This body is. now recognised to be a mixture of two isomeric ketones, known as a-ionone and j8-ionone. The commercial article, which is a mixture of the two ketones has approximately the following characters —... 

Although the odour of the pseudo-ionone does not appear to render it of great importance for its direct use in perfumery, it is capable of serving as raw material lor the production of perfumes, the pseudo-ionone being converted by the action of dilute acids into an isomeric ketone, which I term lonone, and which has most valuable properties for perfumery purposes. This conversion may be effected, for example, by heating for several hours in an oil-bath 20 parts of pseudo-ionone with 100 parts of water, 2-5 parts of sulphuric acid, and 100 parts of glycerine, to the boiling-point of the mixture. 

Hydrocarbon A has the formula C9HI2 and absorbs 3 equivalents of H to yield B, C9H]g, when hydrogenated over a Pd/C catalyst. On treatment of A with aqueous H2S04 in the presence of mercury(d), two isomeric ketones, C and D, are produced. Oxidation of A with KMn04 gives a mixture of acetic acid (CH3C02H) and the tricarboxylic acid E. Propose structures for compounds A-D, and write the reactions. 

Hydroboration-oxidation of 1,4-di-f-butylcyclohexene gave three alcohols 9-A (77%), 9-B (20%), and 9-C (3%). Oxidation of 9-A gave a ketone 9-D that was readily converted by either acid or base to an isomeric ketone 9-E. Ketone 9-E was the only oxidation product of alcohols 9-B and 9-C. What are the structures of compounds 9A-9E ... 

A number of stereospecific intramolecular Diels-Alder reactions of trienones leading to c -fused products have been described. The ketone 34 forms solely compound 35 on treatment with aluminium trichloride at 110°C (equation 25)30. The lower homologue 36 undergoes a spontaneous cyclization to 37 below 20 °C (equation 26)31 and the isomeric ketones 38 and 40 similarly give 3932 and 4133, respectively (equations 27 and 28). 

The scope and limitations of the Fe(CO)s-catalyzed isomerization of allylic alcohols was investigated in detail. This study revealed that the treatment of secondary allylic alcohols with 10-20 mol% Fe(CO)s at 110-125 °C for 2-6 h gave isomerized ketones in 60-80% yield with >95% purity.31... 

Radical-chain processes that are usually operative in the auto-oxidation of free cod [73] can produce olefin oxygenation in some instances. This is the case of the reaction of [Ir(ri -CpO(cod)] (Cp = 3,5-(Me3Si)2Cp) [74] with dioxygen in tetrachloroethane (TCE) under reflux, where a free-radical chlorine-photosensitized oxidation gave two isomeric ketones (Eq. 18). 

Hydration of allene and mono- and disubstituted allenes leads to ketones through the rearrangement of the intermediate enols.29 Further details of the mechanism are not known, but protonation of the terminal carbon in monosubstituted allenes is probable. Although the formation of isomeric ketones may be expected, only ketones possessing the keto function on the central carbon of the allene bond system were found to form.30 When alcohols add to allenes, enol ethers of the corresponding ketones are usually the products. They may further react to form acetals. Hg2+ salts may be used as catalysts.31... 

Two new reactive, very powerful organic peroxides, dimethyldioxirane and methyl(trifluoromethyl)dioxirane (4), have been introduced.81-83 The latter is more reactive and can be used more conveniently.84 85 Acyclic alkanes give a mixture of isomeric ketones on oxidation with methyl(trifluoromethyl)dioxirane,84,85 while cyclohexanone is the sole product in the oxidation of cyclohexane (99% selectivity at 98% conversion).85 With the exception of norbomane, which undergoes oxidation at the secondary C-2 position, highly selective tertiary hydroxylations can be carried out with regioselectivities in the same order of magnitude as in oxidations by peracids.85-87 A similar mild and selective tertiary hydroxylation by perfluorodialkyloxaziridines was also reported.88 Oxidation with dioxiranes is highly stereoselective 85... 

Figure 22-10 Election ionization (70 eV) mass spectra of isomeric ketones with the Composition C4H,20. [From NIST/EPA/MH Mass Spectral Database.8]...

Mass spectra of isomeric ketones with the composition from... 

Exercise 26-16 Reduction of 9,10-anthracenedione with tin and hydrochloric acid in ethanoic acid produces a solid, pale-yellow ketone (mp 156°), which has the formula C14H10O. This ketone is not soluble in cold alkali but does dissolve when heated with alkali. Acidification of cooled alkaline solutions of the ketone precipitates a brown-yellow isomer of the ketone (mp 120°), which gives a color with ferric chloride, couples with diazonium salts (Section 23-1OC), reacts with bromine, and slowly reverts to the isomeric ketone. 

Benzo[6]thienyl)propionic acid is obtained by dehydrogenation of the spirolactone (144) it undergoes cyclization in the presence of liquid hydrogen fluoride to give the isomeric ketones (307 and 308).447 j9-(3-Benzo[6]thienyl)propionyl chloride and its a-methyl derivative... 

The initially formed chromate ester is fragmented, producing an allylic cation that can be attacked at two positions by a chromate anion. The resulting allylic chromates evolve by producing two isomeric ketones. 

The presence of a substituent at a distant position from the double bond provides for the formation of isomeric ketones, in most cases keeping the high total selectivity. For example, 4-methyl-l-cyclohexene (entry 5) and 4-(3-cyclohexen-l-yl)pyridine (entry 6), having substituents in position 3, give the two expected isomeric ketones with total selectivities 95% and 97%, respectively. In the case of (6-methyl-3-cyclohexen-l-yl)methanol (entry 7), the selectivity is lower, which seems to be caused mainly by dehydration of the alcohol. 

Methylcyclohexenone 281 upon oxidation with Mn(OAc)3 in benzene under reflux gave 282, which reacted with phenylmagnesium chloride and CuBr-Me2S to form two isomeric ketones 283 and 284. Further, 283 has been transformed to vinylsilane 285 followed by its hydrolysis to form the free alcohol 286, which in turn was alkylated with methoxyallyl bromide to give 287. Oxalic acid-mediated deprotection of 287 led to the formation of the ketone 288. Ozonolysis of 288 in methanol afforded the fused 1,2,5-trioxepine 289 in low yields (Scheme 66) <1997BML2357>. 

A more challenging example is the isomeric ketone 26. The same two disconnections reveal two enones 27 and 28. This time the regioselectivity of the 2 + 2 cycloadditions is wrong in both cases but again we are not unduly concerned as they will be intramolecular. 

The products, formed in yields above 70%, were the benzhydrindones XXXIV and XXXVI, respectively.18 None of the isomeric ketones was found. 

The Benzene Nucleus. The main problem in direction of cyclization is presented when both positions ortho to the acid side chain are available and ring closure into both would result in the formation of two isomeric ketones. In the benzene series the only acids having these structural properties are the meta substituted phenylbutyric and phenylpropionic acids, with which cyclization usually takes place at the position para to the substituent. Thus 6-methoxytetralone-l (LIV) was obtained14... 

In an acylation reaction which gives a mixture of isomeric ketones, the proportion of these isomers can sometimes be altered more or less by changing (a) the solvent, (b) the temperature, and (c) the entire method of acylation. To what extent the proportion of products may be altered, if at all, by such experimental changes cannot be predicted. 

For all but the most symmetrical trimers, two distinct cyclocondensations can be identified as potential synthetic routes starting from two isomeric ketones (e.g., 13 = 15). 

The head-to-head and head-to-tail configuration of the isomeric ketones (7) and (8) were discernable. A slight distortion of the cyclobutane ring in compound (7) suggests an imbalance in steric strain <81CJC3136>. 

A minor product observed in the photolysis of DBK in aqueous HDTCl (Fig. 5) is the isomeric ketone 4-methylphenylacetophenone (PMAP, 3) 15 18). The question arises as to whether the formation of 3 is due to some special orienting feature of the micelle which operates on the ratio of coupling products 1 and 3. Although 3 has not been detected by the conventional analytical methods for product analyses, (e.g., vpc), some 3 is detectable via chemically induced dynamic nuclear polarization (CIDNP) measurements 28). Thus, it may be that the ratio of formation of 1 to 3 is similar in both micellar and homogeneous solutions, but that the absolute yield of both combination products is so much smaller in homogeneous solution that 3 is not detectable by conventional analyses. 

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