Chain branching ketones

The branched-chain polyunsaturated ketones tagetone and ocimenone, the odor impact compounds ia tagettes, are unstable and presumably responsible for the resiniftcation of the oil. 

The regiochemical course reacting saturated ketones depended on the substitution pattern of the a-positions. In most cases, the intermediate oxime had an anti N-OH function with respect to the chain branched a-position. Consequently, the more substituted alkyl group preferentially migrates. This advantage was utilized for synthesizing the spiro a-amino-e-caprolactam (202 203, Scheme 38) [12c], the Mexican bean beetle azamacrolide allomone (205 206, Scheme 39) [44 a], in a key step of the chiral synthesis of benzomorphanes... 

Aliphatic ketones are oxidised in both acetonitrile [1,2] and trifluoracetic acid [3] at potentials less positive than required for the analogous hydrocarbons. The oxidation process is irreversible in both solvents and cyclic voltammetry peak potentials are around 2.7 V V5. see. Loss of an electron from the carbonyl oxygen lone pair is considered to be the first stage in the reaction. In acetonitrile, two competing processes then ensue. Short chain, a-branched ketones cleave the carbon-carbonyl bond to give the more stable carbocation, which is then quenched by reaction with... 

The slow combustion reactions of acetone, methyl ethyl ketone, and diethyl ketone possess most of the features of hydrocarbon oxidation, but their mechanisms are simpler since the confusing effects of olefin formation are unimportant. Specifically, the low temperature combustion of acetone is simpler than that of propane, and the intermediate responsible for degenerate chain branching is methyl hydroperoxide. The Arrhenius parameters for its unimolecular decomposition can be derived by the theory previously developed by Knox. Analytical studies of the slow combustion of methyl ethyl ketone and diethyl ketone show many similarities to that of acetone. The reactions of methyl radicals with oxygen are considered in relation to their thermochemistry. Competition between them provides a simple explanation of the negative temperature coefficient and of cool flames. 

High Temperature Reaction. Reaction in the high temperature regime produces carbon monoxide, water, methane, formaldehyde, and methanol (8) the two higher ketones also form ethylene (I). The intermediate responsible for chain branching appears to be formaldehyde. The concentration of formaldehyde and the rate of reaction run parallel over the whole of the reaction, as shown in Figure 4 for diethyl ketone. 

D. Horton and E. K. Just, Stereospecific chain-branching by C-alkylation at the ketonic and enolic positions of l,6-anhydro-2,3-0-isopropylidene-beta-D-lyxo-hexopyranos-4-ulose, Carbohydr. Res. IS 81 (1971). D. C. Baker, D. K. Brown, D. Horton, and R. G. Nickol, Synthesis of branched-chain sugar derivatives related to algarose, Carbohydr. Res. 32 299 (1974). 

Ketones of great structural variety may therefore be prepared by careful selection of the starting /7-keto ester (cf. Section 5.14.3, p. 736) and the alkyl halides. The standard procedure is illustrated for the preparation of hexan-2-one from ethyl acetoacetate (Expt 5.95), and it may be suitably adapted to the preparation of most alkyl (straight-chain and branched-chain) methyl ketones. 

Note. (1) This method has been successfully applied to a very large range of straight and branched chain aliphatic ketones. 

Like secondary alcohols, ketones are not common constituents of the cuticular lipids of insects (Lockey, 1988). The cuticular lipid of the female housefly, M. domestica, contains 6% of an unsaturated ketone, (Z)-14-tricosen-10-one (Uebel et al., 1978) and lesser amounts of tricosan-10-one and heptacosen-12-one (Mpuru et al 2001). The cuticular lipids of several species of Drosophila contain C13-C17 saturated and unsaturated ketones, including 2-tridecanone and 2-pentadecanone in Drosophila hydei (Moats et al., 1987), 10-heptadecen-2-one in D. mulleri (Bartelt et al., 1989), and 2-pentadecanone in D. busckii (Schaner et al., 1989). Odd-chain ketones (2-nonadecanone, 2-heneicosanone and 2-tricosanone) comprise 1% and 3% of adult male and female cuticular lipids, respectively, of the pecan weevil, Curculio caryae (Espelie and Payne, 1991). The cuticular lipids of mature screwworm females, C. hominivorax, contained small quantities of two C31 ketones the symmetrical ketone, 16-hentriacontanone and the methyl-branched ketone, 21-methyl-7-hentriacontanone (Pomonis etal., 1993). 

LAH reduces all three ketones and gives only one of the two possible diastereoisomeric alcohols designated the a-racemate in the cases of the branched chain ketones. The branched ketones give a//3 mixtures after treatment with sodium propanol from which the major (/3) isomer may be isolated. Similar results follow reduction of antipodal forms of methadone and isomethadone.(38) Both racemic methadols are inferior in potency to methadone (a, 0.08 yS, 0.2 methadone, 1) in the MHP test, but activity is more than restored on O-acetylation (a-acetate, 1.3 13-2). Racemic a-acety-... 

Because of the relative rates of chain propagation versus chain walking, polymers from the bis(imine) catalysts can be quite different depending on the metal. Nickel complexes form polymers with mostly shorter-chain branches and more crystallinity while polyethylene from the palladium analogs is more highly branched, to the point it can be amorphous. The palladium complexes also have the abihty to incorporate remarkably high (1 10 mole percent) amounts of polar monomers such as methyl acrylate and methyl vinyl ketone, though at considerable loss in activity. ... 

As shown in Scheme 1.55, chain branching by thermolysis or photolysis, reaction (4), of polymer hydroperoxides (POOH) results in the formation of very reactive polymer alkoxy radicals (PO-) and hydroxyl radicals ( OH). The highly mobile hydroxyl and polymer alkoxy radical can abstract hydrogen atoms from the same or a nearby polymer chain by reactions (5) and (6), respectively (Zweifel, 1998). These polymer oxy radicals can react further to result in p-scission, by reaction (13), or the formation of in-chain ketones by reaction (14), as shown in Scheme 1.57, or can be involved in termination reactions. 

With acyclic and alicyclic ketones regiocheraical complications can arise from alternative modes of enolization. With acyclic compounds there is the additional complication of geometrical isomers. Direction of enolization is usually in accord with thermodynamic stability thus butan-2-one gives ( )-80 and (Z)-81 forms of 3-chloro-2-methyl-2 butenal (Eq. 75). Chain branching at the a or p carbon... 

Baeyer-Villiger oxidation of alkyl- and aryl-substituted C -C, cycloalkanones, steroid ketones and branched chain aliphatic ketones is catalysed by arsonated polystyrene resins [53], Larger size cycloalkanones and linear ketones react much slower. Water miscible and immiscible solvents can be used. With the latter, the resin behaves as an effective catalyst and a phase-transfer agent (triphase catalysis). The same compounds are also epoxidation catalysts. More recently, a method for the preparation of phenols by the oxidation of aromatic aldehydes and ketones has been reported. The most convenient catalysts are nitro-substituted arylseleninic acids and corresponding diselenides [54]. 

Branched C-chains s. Ketones, brandied Bridged compds. s. [lOJAnnulenes, bridged. Diaryls, -, Heterocyclics, -Bridgehead azides, ring expansion 31, 176... 

One other possibility for the identification of ketones is the deformation vibration of the C=0 group. The group —CO—CH3 gives rise to three bands associated with this mode [51], near 600, 500 and 400 cm", but considerable alterations follow chain branching if this occurs near to the carbonyl group, so that the bands cannot be identified in methyl zsopropyl ketone. This correlation is therefore mainly of academic interest. 

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