Carbonyl compounds formation

KMn04 impregnated alumina oxidizes arenes to ketones within 10-30 min under solvent-free conditions using focused microwaves [111]. /i,/i-Disubstituted enamines have been successfully oxidized into carbonyl compounds with KMn04-Al203 in domestic (255 W, 82 °C) and in focused microwave ovens (330 W, 140 °C) under sol-vent-free conditions by Hamelin et al. [112]. The yields are better in the latter case. When the same reactions are conducted in an oil bath at 140 °C, no carbonyl compound formation is observed (Scheme 6.36). 

Alkylation of enolates with a-halo carbonyl compounds. (Formation of 1,4-dicarbonyl compounds)... 

It is now generally admitted that this reaction involves both one-electron and two-electron transfer reactions. Carbonyl compounds are directly produced from the two-electron oxidation of alcohols by both Crvl- and Crv-oxo species, respectively transformed into CrIV and Crm species. Chromium(IV) species generate radicals by one-electron oxidation of alcohols and are responsible for the formation of cleavage by-products, e.g. benzyl alcohol and benzaldehyde from the oxidation of 1,2-diphenyl ethanol.294,295 The key step for carbonyl compound formation is the decomposition of the chromate ester resulting from the reaction of the alcohol with the Crvl-oxo reagent (equation 97).296... 

It is very hard to compare results reported in the literature, as there are various variables influencing the data. Concentration of reactants, ratio of amine compound to sugar or carbonyl, reaction in buffer or water, molarity and type of buffer used, pH of buffer, duration of reaction. Rate of carbonyl compounds formation will be the criterion used for reactivity except in few occasions where the percent loss of one of the reactants or both will be referred to in the manuscript. 

Condensation with carbonyl compounds. Formation of epoxides from aldehydes by reaction with sulfonium ylides is subject to asymmetric induction. The latter species have been generated from 91, 92, and 93, and also those derived from monoterpenes, e.g., 94 " and 95.- Of course the ylides can be obtained in situ by deprotonation of sulfonium salts or copper-catalyzed decomposition of diazoalkanes (with the carbenoids trapped by the sulfides). 

Pyrolysis of sulfoxides provides a convenient method for introducing unsaturation at the position a- to carbonyl compounds. Formation of the enolate and reaction with dimethyl (or diphenyl) disulfide gives the a-methylthio (or phenylthio) derivative. Oxidation with a suitable oxidant, such as mCPBA or NaI04, gives the sulfoxide, which eliminates sulfenic acid on heating to give the a,(3-unsaturated carbonyl compound. For example, the methyl ester of a pheromone of queen honey bees was synthesized from methyl 9-oxodecanoate after initial protection of the ketone as the acetal (2.24). The -isomer usually predominates in reactions... 

The carbonyl compounds could possibly originate from the oxidation of residual organic species and from the presence of a small fraction of insoluble metal carbonate impurities [17]. Scheme 2.5 depicts another proposed mechanism of carbonyl compound formation involving oxidation of alkenes. 

The biradicals formed from (21) and (23), respectively, are primarily produced in their singlet state, but intersystem crossing to the triplet diradical results, followed by carbon-carbon bond cleavage. As CO2 formation from dioxetanones is more exothermic than carbonyl compound formation from tetramethyl dioxe-tan, it is supposed that C-C bond breakage follows more rapidly, reducing the time available for singlet to triplet conversion. As a result, the yield of excited singlet states is nearly the same in both compounds. The yield of excited triplets, however, is much smaller in the dioxetanone case. 

Reactions with Carbonyl Compounds Formation of Cyclopentadiene or 2,5-Dihydrofuran Derivatives... 

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