Reactions of ketones

The fluorination of MejCO with cobalt(III) fluoride at 60 C results in total cleavage into COFj, CHFj, MeF, CH F, CH3C(0)F and CHjFC(0)F. Similarly, MeEtCO (at 

50 C) and Et CO (at 105 C) both give COFj, along with other fluorinated cleavage 

gave COFj and COj in a 2 1 ratio as the only carbon-containing products (no 

Passage of 2-heptafluoropropylcyclohexan-l-one saturated with Ij through a carbon arc gave COFj, along with a mixture of Cj and C3 perfluorinated alkanes [623]. 

Aldol reactions of cyclic ketones with aldehydes. 

Aldol reactions of acyclic ketones with aldehydes. 

The aldol reactions of titanium enolates generated in situ were reported by Harrison [27] to give excellent yield and selectivity for syn aldol products, as shown in Table 2.10. However, methyl ketones tended to eliminate under the reaction conditions and provided a,/i-unsaturated ketones. Reactions with propiophenone and benzaldehyde provided excellent yields of aldolates, with syn aldols being the major product (95 5 ratio). The stereochemical outcome was rationalized by Zimmerman-Traxler transition state model 67. 

Evans used a combination of titanium tetrachloride and diisopropylethyl-amine, which proved to be efficient and general for many different kinds of substrates [28]. The syn aldol diastereoselectivity was comparable with that of boron-mediated processes. Isolated yields with titanium enolates are considerably higher than from boron enolates. Furthermore, syn-selectivity 

Aldol reactions of directly generated titanium enoiates. 

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Most of the characteristic reactions of ketones (RR CO) depend upon condensation with substituted amines. The reactions occur between the carbonyl group and the —NHj group of the substituted amine, and hence are also shared by aldehydes RHCO ... 

Reactions of ketones use acetone reactions (i), (ii), (iii) and (vi) as for aldehydes cycZohexanone oxime (J scale), cycZohexanone phenyl-hydrazone, and acetone semicarbazone (J scale) as in 111,74. ... 

A useful catalyst for asymmetric aldol additions is prepared in situ from mono-0> 2,6-diisopropoxybenzoyl)tartaric acid and BH3 -THF complex in propionitrile solution at 0 C. Aldol reactions of ketone enol silyl ethers with aldehydes were promoted by 20 mol % of this catalyst solution. The relative stereochemistry of the major adducts was assigned as Fischer- /ir o, and predominant /i -face attack of enol ethers at the aldehyde carbonyl carbon atom was found with the (/ ,/ ) nantiomer of the tartaric acid catalyst (K. Furuta, 1991). 

The reaction of ketones with peroxy acids is both novel and synthetically useful An oxygen from the peroxy acid is inserted between the carbonyl group and one of the attached car bons of the ketone to give an ester Reactions of this type were first described by Adolf von Baeyer and Victor Vilhger m 1899 and are known as Baeyer—Villiger oxidations... 

The a-hydioxypyiioles, which exist piimadly in the tautomeric pyiiolin-2-one form, can be synthesized either by oxidation of pyrroles that ate unsubstituted in the a-position or by ting synthesis. P-Hydtoxypyttoles also exist primarily in the keto form but do not display the ordinary reactions of ketones because of the contributions of the polar form (25). They can be teaddy O-alkylated and -acylated (41). 

Schmidt reaction of ketones, 7, 530 from thienylnitrenes, 4, 820 tautomers, 7, 492 thermal reactions, 7, 503 transition metal complexes reactivity, 7, 28 tungsten complexes, 7, 523 UV spectra, 7, 501 X-ray analysis, 7, 494 1 H-Azepines conformation, 7, 492 cycloaddition reactions, 7, 520, 522 dimerization, 7, 508 H NMR, 7, 495 isomerization, 7, 519 metal complexes, 7, 512 photoaddition reactions with oxygen, 7, 523 protonation, 7, 509 ring contractions, 7, 506 sigmatropic rearrangements, 7, 506 stability, 7, 492 N-substituted mass spectra, 7, 501 rearrangements, 7, 504 synthesis, 7, 536-537... 

Reaction of ketones with S-ylides denved from Me3S t or Me3SO I to give epoxides... 

The mechanistic pattern established by study of hydration and alcohol addition reactions of ketones and aldehydes is followed in a number of other reactions of carbonyl compounds. Reactions at carbonyl centers usually involve a series of addition and elimination steps proceeding through tetrahedral intermediates. These steps can be either acid-catalyzed or base-catalyzed. The rate and products of the reaction are determined by the reactivity of these tetrahedral intermediates. 

Enolates of aldehydes, ketones, and esters and the carbanions of nitriles and nitro compounds, as well as phosphorus- and sulfur-stabilized carbanions and ylides, undergo the reaction. The synthetic applications of this group of reactions will be discussed in detail in Chapter 2 of Part B. In this section, we will discuss the fundamental mechanistic aspects of the reaction of ketone enolates with aldehydes md ketones. 

The dominant photochemical reaction of ketones in the gas phase is cleavage of one of the carbonyl substituents, which is followed by decaibonylation and sidsoetprait reactions of the alkyl free radicals that result ... 

As is clear from the preceding examples, there are a variety of overall reactions that can be initiated by photolysis of ketones. The course of photochemical reactions of ketones is veiy dependent on the structure of the reactant. Despite the variety of overall processes that can be observed, the number of individual steps involved is limited. For ketones, the most important are inter- and intramolecular hydrogen abstraction, cleavage a to the carbonyl group, and substituent migration to the -carbon atom of a,/S-unsaturated ketones. Reexamination of the mechanisms illustrated in this section will reveal that most of the reactions of carbonyl compounds that have been described involve combinations of these fundamental processes. The final products usually result from rebonding of reactive intermediates generated by these steps. 

Like the reaction of ketones, the interaction of triflic anhydride with thiourea and substituted thioureas also gives dicationic triflates (equations 40 and 41) however, two sulfur atoms form the bndge in this case This result indicates that triflic anhydride is acting as an oxidizing reagent toward thiourea [89]. 

On the other hand y-pyrones or 1,3-diketones could be obtained from the reactions of ketone derived enamines with diketene 423-426). The addition of dimethyl ketene dimer to aldehyde or ketone derived enamines produced cyclohexanediones 425,426). 

Thiohydantoin 9 was obtained from the treatment of carbonyl 1 with carbon disulfide and ammonium cyanide in aqueous methanol. The transformation could also be carried out step-wise, that is, treatment of 1 with ammonium cyanide to form aminonitrile 10 followed by reaction with carbon disulfide to produce thiohydantoin 9. Alternatively, 5,5-disubstituted 4-thiohydantoins could be prepared by the reaction of ketones with ammonium monothiocarbamate and sodium cyanide. ... 

In most cases, however, many substrates give a mixture of stereoisomers with a certain degree of stereoselectivity. When ketone 39 was treated with potassium cyanide and ammonium carbonate in ethanol/water, a mixture of epimeric hydantoins 40 and 41 were isolated.Similarly, the Bucherer-Bergs reaction of ketone 42 gave rise to a... 

Preparation of oxetanes by [2- -2]-photocycloaddition reactions of ketones and dienes 98S683. 

Because ketones are generally less reactive than aldehydes, cycloaddition reaction of ketones should be expected to be more difficult to achieve. This is well reflected in the few reported catalytic enantioselective cycloaddition reactions of ketones compared with the many successful examples on the enantioselective reaction of aldehydes. Before our investigations of catalytic enantioselective cycloaddition reactions of activated ketones [43] there was probably only one example reported of such a reaction by Jankowski et al. using the menthoxyaluminum catalyst 34 and the chiral lanthanide catalyst 16, where the highest enantiomeric excess of the cycloaddition product 33 was 15% for the reaction of ketomalonate 32 with 1-methoxy-l,3-butadiene 5e catalyzed by 34, as outlined in Scheme 4.26 [16]. 

The absolute configuration of the cycloaddition product obtained by the reaction of ketones with activated dienes catalyzed by (S)-t-Bu-BOX-Cu(II) (S)-21b points also to an intermediate in which the geometry around the central copper atom is square-planar similar to 26 above, and that the diene approaches the carbonyl functionality in an endo fashion. 

Several pairs of reactants are possible. The aldol reaction between two molecules of the same aldehyde is generally quite successful, since the equilibrium lies far to the right. For the analogous reaction of ketones, the equilibrium lies to the left, and the reaction conditions have to be adjusted properly in order to achieve satisfactory yields (e.g. by using a Soxhlet extractor). 

The Schmidt reaction of ketones works best with aliphatic and alicyclic ketones alkyl aryl ketones and diaryl ketones are considerably less reactive. The reaction is only seldom applied to aldehydes as starting materials. The hydrazoic acid used as reagent is usually prepared in situ by treatment of sodium azide with sulfuric acid. Hydrazoic acid is highly toxic, and can detonate upon contact with hot laboratory equipment. 

To anticipate briefly, shortening the length of the side chain in the phenothiazines from three to two carbon atoms changes I he activity of the products from neuroleptics to antihistaminic iigents. A rather similar effect is seen in the tricyclic antidepressants. Reaction of ketone, 27, with the Grignard reagent I rom 4-chloro-l-methylpipyridine (35) affords the tertiary alco-liol, 36. Dehydration gives the antihistamine, cyproheptadine (37). ... 

The Henry reaction of ketones with nitroalkanes in the presence of etbylenediamine gives allylic nitro compounds, which give a,fi-imsanirated carbonyl compounds via the Nef reaction fEq. 6.30. ... 

Michael additions followed by further Michael additions have become popular reactions and are usually referred to as Michael Michael Induced Ring Closure (MIM1RC) reactions. A three component Michael-Michael-aldol reaction of ketone enolates with acrylates can be achieved, resulting in the formation of six-membered ring compounds with good efficiency and high diastereoselectivites319. 

The reaction of ketones with tosylmethylisocyanide (31) gives different products, depending on the reaction conditions. 

In the first step of the mechanism, the OH group is converted by the reagent to a better leaving group (e.g., proton acids convert it to OHj). After that, the mecha-nism follows a course analogous to that for the Schmidt reaction of ketones (18-16) from the formation of 71 on ... 

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