Ketones simple

Both aldoses and ketoses reduce Fehling s solution (for details, see under 4). This fact may appear surprising when it is remembered that Fehling s solution is one of the reagents for distinguishing between aldehydes and ketones (see 4). The explanation lies in the fact that a-hydroxyketones are much more readily oxidised than simple ketones, perhaps because the hydroxy ketone allows its isomerisation, in the presence of alkali, into an aldehyde. For example, fructose, a keto-hexose, might Isomerlse thus ... 

No intennolecular reaction of malonate or /3-keto esters with halides has been reported, but the intramolecular reaction of /3-diketones such as 790 and malonates proceeds smoothly[652,653]. Even the simple ketone 791 can be arylated or alkenylated intramolecularly. In this reaction, slow addition of a base is important to prevent alkyne formation from the vinyl iodide by elim-ination[654]. 

Simple ketones and esters are inert. On the other hand, nitroalkanes react smoothly in r-butyl alcohol as a solvent with butadiene, and their acidic hydrogens are displaced with the octadienyl group. From nitromethane, three products, 64, 65, and 66, are formed, accompanied by 3-substituted 1,7-octadiene as a minor product. Hydrogenation of 65 affords a fatty amine 67 which has a primary amino function at the center of the long linear chain[46,61]. 

Class (2) reactions are performed in the presence of dilute to concentrated aqueous sodium hydroxide, powdered potassium hydroxide, or, at elevated temperatures, soHd potassium carbonate, depending on the acidity of the substrate. Alkylations are possible in the presence of concentrated NaOH and a PT catalyst for substrates with conventional pX values up to - 23. This includes many C—H acidic compounds such as fiuorene, phenylacetylene, simple ketones, phenylacetonittile. Furthermore, alkylations of N—H, O—H, S—H, and P—H bonds, and ambident anions are weU known. Other basic phase-transfer reactions are hydrolyses, saponifications, isomerizations, H/D exchange, Michael-type additions, aldol, Darzens, and similar... 

Enols of simple ketones can be generated in high concentration as metastable species by special techniques. Vinyl alcohol, the enol of acetaldehyde, can be generated by very careful hydrolysis of any of several ortho ester derivatives in which the group RC02 is acetate acid or a chlorinated acetate acid. ... 

Solutions of unstable enols of simple ketones and aldehydes can also be generated in water by addition of a solution of the enolate to water. The initial protonation takes place on oxygen, generating the enol, which is then ketonized at a rate that depends on the solution pH. The ketonization exhibits both acid and base catalysis. Acid catalysis involves C-protonation with concerted 0-deprotonation. 

Nal, CeCl3 7H20, CH3CN, rt, 0.5-21 h, 84-96% yield. Chemoselective cleavage of ketone derivatives is observed in the presence of aldehyde derivatives, and enone ketals are cleaved in the presence of simple ketone ketals. 

Reaction of tryptamine with simple ketones has not been widely explored. Acetone in the presence of benzoyl chloride has been reported to yield 2-benzoyl-1,1 -dimethyl-1,2,3,4-tetrahydro-j8-carbo-line. That the keto group is much less reactive than the aldehyde group is indicated by the fact that j8-keto aldehydes, in the form of their acetals or sodium salts, react with tryptamine at the aldehyde function to yield the conjugated enamine 24, which undergoes ring closure via an intramolecular Michael addition. The potentialities of this interesting modification of the Pictet-Spengler reaction have not yet been fuUy explored. 

Thus, simple ketones or aliphatic aldehydes may be successfully used as starting materials in the CSIC (Carbanion mediated Sulfonate Intramolecular Cyclization) reaction. Ai-alkylsulfonamides could be also cyclized under CSIC conditions (99T(55)7625) affording the spiroisothiazoline 79. By treatment with TMSCl, Nal in acetonitrile at r.t., hydrolysis of the enamine and formation of the corresponding keto derivative 80 was obtained. 

This method is illustrative of a general method of preparing simple ketones from normal aliphatic carboxylic acids. It is especially useful because the starting materials are easily accessible, the yields good, and the procedure very simple. 

Carbons adjacent to a Z group (as defined on p. 548) can be nitrosated with nitrous acid or alkyl nitrites. The initial product is the C-nitroso compound, but these are stable only when there is no tautomerizable hydrogen. When there is, the product is the more stable oxime. The situation is analogous to that with azo compounds and hydrazones (12-7). The mechanism is similar to that in 12-7 R—H —> R + N=0 — R—N=0. The attacking species is either NO or a carrier of it. When the substrate is a simple ketone, the mechanism goes through the enol (as in halogenation 12-4) ... 

In an indirect method of achieving this conversion, the silyl enol ether of a simple ketone is treated with or with triphenylmethyl cation (for another indirect... 

Alternatively, Cushman has devised a facile route to pyrroles by the reaction of Boc-a-amino aldehydes or ketones 14 with the lithium enolates of ketones 15 to afford aldol intermediates 16 which cyclize to pyrroles 17 under mild acidic conditions <96JOC4999>. This method offers several advantages over the Knorr since it employs readily available Boc-a-amino aldehydes or ketones and utilizes simple ketones instead of the p-diketo compounds or p-keto esters normally used in the Knorr. 

Grignard addition to COg must be the answer with this crowded acid and this leads us back to alcohol (20), Disconnection of any group now gives a simple ketone and an available alkyl halide. As we shall see in Chapter 11, it is best to divide the molecule into two nearly equal parts, so we shall use disconnection (a). 

Compare these two routes to the simple ketone (33) and the one used on page T 130, Which disconnection and which synthons are used in each approach ... 

Immediate disconnection (13a) of the three-membered ring gives a very complicated starting material (14) so it is better to simplify the left hand portion of the molecule first. Disconnection (13b) is good as it leaves simple ketone (16) and an allylic halide (15). 

In contrast to aldehydes, simple ketones are poor substrates for Fe-catalyzed olefinations due to their weak electrophilicity. Decreasing the electron density of carbonyl group can facilitate olefination of ketones with diazo compounds. 

Not all carbon nucleophiles will add to arene chromium tricarbonyl complexes. For example, alkyllithium reagents and simple ketone enolates do not give adducts.325... 

In Chapter 2 we discussed a number of techniques used to study the various photophysical and photochemical processes occurring in anthracene and similar molecules. In that discussion we were primarily interested in the singlet state. In this chapter we will discuss some of the techniques available for studying the photophysical and photochemical properties of the triplet state. Most of our discussion will be directed to the photochemistry of simple ketones. 

It is well known that neutral simple ketones 163 in general are more stable than their isomeric enol form 164b0 6l). However, for the corresponding cation radicals 165 and 166 it has been shown both experimentally62,63) and computationally64,65 that, depending on the substituent R, the ionized ketones 165 are significantly less stable than their isomeric enol cation radicals 166 (41). Moreover, CA spectroscopy... 

For even simple ketones, e.g. propanone (90), the equilibrium is found to lie far over to the left ( 2 % of 91)—reflecting the less ready attack of the carbanion (92) on a keto (90), rather than on an aldehydo (88, above), carbonyl carbon atom ... 

The generally accepted mechanism of homogeneous hydrogenation of simple ketones seems to occur by a [7r2 + cr2] pathway as depicted in Scheme 16. 

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