Of alkyl ketones

Among other methods for the preparation of alkylated ketones are (1) the Stork enamine reaction (12-18), (2) the acetoacetic ester synthesis (10-104), (3) alkylation of p-keto sulfones or sulfoxides (10-104), (4) acylation of CH3SOCH2 followed by reductive cleavage (10-119), (5) treatment of a-halo ketones with lithium dialkyl-copper reagents (10-94), and (6) treatment of a-halo ketones with trialkylboranes (10-109). 

NHC-promoted enolate formation from an enal, followed by a desymmetrising aldol event to generate P-lactones and loss of CO, has been exploited by Scheidt and co-workers to generate functionalised cyclopentenes 240 in high ee from enal substrates 238 (Scheme 12.52) [94]. Interestingly, the use of alkyl ketones in this reaction manifold allows the isolation of the p-lactone intermediates with acyclic diketones, P-lactones 239 are formed with the R group anti- to the tertiary alkox-ide, while with cyclic diketones the P-lactone products have the R group with a syn relationship to the alkoxide [95]. 

The quantum yields for oxetane formation have not been determined in every case, and only a few relative rate constants are known. The reactivities of singlet and triplet states of alkyl ketones are very nearly equal in attack on electron rich olefins. 72> However, acetone singlets are about an order of magnitude more reactive in nucleophilic attack on electron-deficient olefins. 61 > Oxetane formation is competitive with a-cleavage, hydrogen abstraction and energy-transfer reactions 60 64> so the absolute rates must be reasonably high. Aryl aldehydes and ketones add to olefins with lower quantum yields, 66> and 3n-n states are particularly unreactive. 76>... 

Figure 4 illustrates the infrared spectrum for a sample of PPE. The absorptions of the peaks at 3.4, 6.9 and 7.3 pm were assigned to C-H stretch and C-H bending frequencies in CH2 and CH3 (33). These absorptions are proportional to the surface density of deposited ethane (16). However, the absorptions at photons near 10 pm are attributable to OH deformations and CO stretchings of alcoholic groups and vibrations of alkyl ketones (22). They also indicate the existence of branches in unsaturated chain (33). 

In the late 1960s, methods were developed for the synthesis of alkylated ketones, esters, and amides via the reaction of trialkyl-boranes with a-diazocarbonyl compounds (50,51), halogen-substituted enolates (52), and sulfur ylids (53) (eqs. [33]-[35]). Only one study has addressed the stereochemical aspects of these reactions in detail. Masamune (54) reported that diazoketones 56 (Ri = CH3, CH2Ph, Ph), upon reaction with tributylborane, afford almost exclusively the ( )-enolate, in qualitative agreement with an earlier report by Pasto (55). It was also found that E) - (Z)-enolate isomerization could be accomplished with a catalytic amount of lithium phenoxide (CgHg, 16 hr, 22°C) (54). 

The iminophosphoranes of methyl arylhydrazono acetates (338) possessing a keto function in an o-position afford l//-l,2,4-benzotriazepines (339) upon heating (Scheme 123). The yield depends on the substituents and solvents employed. Methoxycarbonyl-, 4-pyridyl-, and 3-pyridyl groups activate the carbonyl function and improve the yield. Reactions of alkyl ketones and aldehydes proved to be unsuccessful [91JCR(S)2],... 

One possible explanation for the lack of correspondence between emitting and reacting states is reaction of the singlet. In the case of benzophenone, there is little question that the reaction involves only the triplet state, since triplet quenchers can effectively inhibit the reaction. This need not be the case with all carbonyl compounds. For example, it has been shown that both the n,ir singlet and triplet states can be involved in the Norrish type II cleavage of alkyl ketones (25-27). At high concentrations, piperylene quenches only that part of the 2-hexanone cleavage which arises from the triplet. The rate constants for... 

Disilanyl enol ethers (22) are the main product of the reaction of alkyl ketones with photochemically generated phenyltrimethylsilylsilylene (Scheme 30) (77JOM(135)C45). They could result from silylene insertion into the enol O—H bond, particularly as many have been isolated from dodecamethylcyclohexasilane and alkyl ketones or aldehydes on photolysis (Scheme 31) (78CL609). 

Using this procedure, large quantities (up to 20 g48) of alkylated ketone 54 were regularly prepared. 

The 3-azapyrylium hexachloroantimonates 204 are also obtained by the reaction of alkyl ketones 201 with benzonitrile in the presence of acylium salts 202 prepared beforehand117 (equation 64). 

The Mannich bases subjected to the replacement reaction arc usually derivatives of alkyl ketones, phenols, and ferrocene. 

An interesting variation has recently been described using 1,3-dichloroacetone for the preparation of alkyl ketones via cyclopropanol intermediates (equation 68). ... 

The present author has investigated the photochemistry of alkyl ketones adsorbed on porous Vycor glass to examine how the reactivity of the excited states or of the radical species themselves varies when they are formed on the solid surfaces. In those studies, we have found that the photochemical reactivities of adsorbed alkyl ketones are markedly different from those in the gas phase, leading to some general characteristics of the photochemistry in the adsorbed layer (5-13). 

This chapter deals with the characteristics of the photolyses of alkyl ketones adsorbed on porous Vycor glass which arises from the electronic perturbation and the steric hindrance effects of the surfaces upon the primary and secondary photochemical processes. The effects of surface hydroxyl groups upon the primary and secondary photochemical processes are also discussed, since surface hydroxyl groups have been found to play a significant role in the photochemistry of the adsorbed... 

EXCITED STATES OF ALKYL KETONES ADSORBED ON VYCOR GLASS... 

As shown in Table 2, the efficiencies of the photolyses of these ketones can be compared acetone (1.0), 2-butanone (34.3), and 2-pentanone (202). A marked difference is seen in their efficiencies, in contrast with essentially the same efficiencies observed for the gas phase photolyses of these ketones (6). From these, together with the results mentioned in section 3, the following conclusion emerges. The photochemical reaction efficiencies of alkyl ketones adsorbed on Vycor glass are decreased on adsorption owing to the increase in their efficiencies of radiationless deactivation and also to the decrease in their extinction coefficients. Thus, the more blue shifs, i. e., the more strongly hydrogen bonded a ketone molecule is, the more efficient radiationless deactivation becomes. 

The photolyses of alkyl ketones have been investigated on Vycor... 

Photochemistry of Alkyl Ketones in the Adsorbed State Effects of Solid Surfaces upon the Photolysis (M. Anpo)... 

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