Epoxidation carbonyl oxides

Thallium-Catalyzed Epoxidation Process. The use of Tl(III) for olefin oxidation to yield glycols, carbonyls, or epoxides is weU known... 

The most common method of epoxidation is the reaction of olefins with per-acids. For over twenty years, perbenzoic acid and monoperphthalic acid have been the most frequently used reagents. Recently, m-chloroperbenzoic acid has proved to be an equally efficient reagent which is commercially available (Aldrich Chemicals). The general electrophilic addition mechanism of the peracid-olefin reaction is currently believed to involve either an intra-molecularly bonded spiro species (1) or a 1,3-dipolar adduct of a carbonyl oxide, cf. (2). The electrophilic addition reaction is sensitive to steric effects. 

ATR-HP IR spectroscopy has also been used to follow the cobalt-catalysed carbonylation of epoxides to give lactones or polyesters [46]. Addition of excess propylene oxide to [HCo(CO)4] (generated in situ by protonation of [Co(CO)4] ) under 20 bar CO was found to give an acyl complex, [Co(C(0)CH2CH(OH)Me)(CO)4]. Depending... 

Epoxidation of alkenes with carbonyl oxides and dioxiranes. 35... 

FIGURE 17. Transition structures for the epoxidation of ethylene by carbonyl oxide [A(E- -ZPVE) = 10.2 kcalmoU ] and dimethylcarbonyl oxide [A(E-I-ZPVE) = 10.3 kcalmol" ] optimized at the B3LYP/6-311- -G(d,p) level of theory. Bond lengths given in brackets are at the MP2/6-31G(d) level, and the corresponding barriers are 14.8 and 12.9 kcalmoU ... 

Ethylene epoxidation with unsubstituted carbonyl oxide is ca 5 kcalmol" more exothermic than with dimethylcarbonyl oxide, yielding an even earlier transition state. 

In summary, transition structures with dioxirane and dimethyldioxirane are unsymmet-rical at the MP2/6-31G level, but are symmetrical at the QCISD/6-31G and B3LYP/6-31G levels. The transition states for oxidation of ethylene by carbonyl oxides do not suffer from the same difficulties as those for dioxirane and peroxyforaiic acid. Even at the MP2/6-31G level, they are symmetrical (Figure 17). The barriers at the MP2 and MP4 levels are similar and solvent has relatively little effect. The calculated barriers agree well with experiment . In a similar fashion, the oxidation of ethylene by peroxyformic acid has been studied at the MP2/6-31G, MP4/6-31G, QCISD/6-31G and CCSD(T)/6-31G and B3LYP levels of theory. The MP2/6-31G level of theory calculations lead to an unsymmetrical transition structure for peracid epoxidation that, as noted above, is an artifact of the method. However, QCISD/6-31G and B3LYP/6-31G calculations both result in symmetrical transition structures with essentially equal C—O bonds. 

Cvetanovic67 was concerned with oxygen atom reactions with unsaturated hydrocarbons. The oxygen atoms were obtained in his experiments by mercury-photosensitized decomposition of N20. Cvetanovi6 came to the conclusion that the reaction of oxygen atoms with ethylene proceeded essentially with scission of the hydrocarbon bond, while with higher olefins this was not observed. Corresponding oxides (epoxides) and carbonyl compounds were formed in the course of the reaction. 

The authors identified the epoxide CH3Cl-COC-CH3Cl that they attributed to the addition of carbonyl oxide (1) to the olefin, which has not been clearly demonstrated [31, 32]. The epoxide formation has also been observed in the case of the ozonization of tetrachloroethylene [33-35] which yielded tri-chloroacetyl chloride (CCl3-CO-Cl) and phosgene (C12C=0) (Scheme 7) and in the case of a highly hindered olefin like compound (Scheme 8). 

Dioxiranes (32) are isomeric with carbonyl oxides (33), one of the peroxidic intermediates involved in the ozonolysis process.9 Dimethyldioxirane (DMDO) (31) epoxidizes the double bond of the protected galactal favoring the Oepoxide 8 with a selectivity of 20 1.10,11 You can use 31 likewise to transform an aldehyde into a carboxylic acid. 

Cyanogen bromide, triazine method, cychc trani-2,3-carbonate reaction, carbonylation, periodate oxidation, epoxide activation Curtis azide rearrangement, coupling reagent method, acid anhydride reaction Schiff base formation reaction... 

In ketone-directed peroxy acid epoxidations of cyclic alkenes the actual epoxidizing agent has been shown by 180-labeling not to involve a dioxirane <94TL6155>. Instead, an a-hydroxy-benzoylperoxide or a carbonyl oxide is believed to be responsible for observed stereoselectivities in the intramolecular epoxidations. The extent of syn-selectivity is greater for ketones than with esters the syn/anti ratios increase when ether is used as solvent rather than CH2C12, the reverse situation for hydroxyl-directed epoxidations. Fused-ring oxiranes can also be prepared from acyclic precursors. Four different approaches are discussed below. 

The metal catalyzed ring opening of epoxides followed by reaction with CO or COj to form P-lactones and carbonates is a useful reaction that continues to attract attention. In an expansion of previous work, Coates and co-workers have developed an improved catalyst, 99, for the carbonylation of epoxides <05JA11426>. These reaction conditions are compatible with a wide variety of side chains, including those bearing Lewis basic functionality. Interestingly, the cyclopentene oxide 97 was readily converted to the P-lactone 98 in excellent yield. 

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