Ozonides acetate

Qeavage of ozonide 64 leads to the formation of long-chain aldehyde acetic acid 1-formyl-hexyl ester (65) and carbonyl oxide 66. Ester 65 was formed almost exclusively, which was attributed to the presence of an acetoxy group in vicinity of the olefinic double bond that might protect the aldehyde from a fast reaction with the carbonyl oxide to the secondary ozonide acetic acid l-[l,2,4]trioxalane-3-yl-hexyl ester (67). However, at higher olefin conversion the selectivity to aldehyde 65 decreases due to the increasing formation of secondary ozonide 67 and side reactions of aldehyde 65. 

Low -molecular-weight ozonides are explosive and are theretore not isolated. Instead, the ozonide is immediately treated with a reducing agent such as zinc metal in acetic acid to convert it to carbonyl compounds. The net result of the ozonolysis/reduction sequence is that the C=C bond is cleaved and oxygen becomes doubly bonded to each of the original alkene carbons. If an alkene with a letrasubstituted double bond is ozonized, two ketone fragments result if an alkene with a trisubstituted double bond is ozonized, one ketone and one aldehyde result and so on. 

Oz.onide (Section 7.9) The product formed by addition of ozone to a carbon-carbon double bond. Ozonides are usually treated with a reducing agent, such as zinc in acetic acid, to produce carbonyl compounds. 

Oxidation Is usually brought about by using the acetic acid/hydrogen peroxide mixture (the acHve species is peracetic acid). Ozonide is highly dangerous, especially when it is insoluble in the medium. 

When ozone is present, vinyi acetate forms an ozonide that is explosive ... 

The ozonide formed by vinyl acetate is explosive when dry. 

Ozonides are not usually isolated but are reduced directly by treatment with znic and acetic acid (HOAc). 

Palladium Paraformaldehyde Paraldehyde Pentaborane-9 Pentacarbonyliron Arsenic, carbon, ozonides, sulfur, sodium tetrahydridoborate Liquid oxygen Alkalies, HCN, iodides, nitric acid, oxidizers Dimethylsulfoxide Acetic acid, nitric oxide, transition metal halides, water, zinc... 

Reduction of ozonides is very useful, especially when aldehydes are the desired products. Ozonides are easily hydrogenolyzed over palladium [670], or reduced by zinc in acetic acid [671], usually in good yields. Ozonolysis of methyl oleate followed by hydrogenation over 10% palladium on charcoal... 

Most of the examples given here involve fairly strong acid catalysts to effect fragmentations. Many ozonides are stable to mild acids, so that if a molecule contains other functionality, chemoselective reactions are possible. Reactions of compounds containing both an aldehyde and ozonide group (88) have been studied. The aldehyde could be protected as an acetal using ethylene glycol with... 

Vinyl acetate reacts with ozone in CDCI3 to give 3-acetoxy-l,2,4-trioxolane (170) (Equation (32)). Benzoyloxy-substituted ozonides (171) can be prepared from cyclic systems such as (172) (Equation (33)) <91JOC1672>. 

Acid-catalyzed condensation of bicyclic ozonides with aldehydes and ketones, in the presence of hydrogen peroxide, leads to the formation of bicyclic peroxide analogs of acetals in low yields, as shown in equation 91 for the condensation of the ozonide of 1-phenylcyclopentene (266) with benzaldehyde. The structure of compound 267, with the preferred ring conformation as shown, was determined by XRD analysis . The same method served to demonstrate that the condensation compound 16c is unique, with structure 254 . 

Procedures. Chromatographic Purification of Ozonization Products. Ozonization products from ethyl 10-undecenoate and 1-octene were chromatographed on silica gel columns (Baker) and eluted with 15 or 25% ether in petroleum ether (b.p., 30°-60°). Fractions were examined by thin-layer chromatography (TLC) on silica gel G Chroma-gram sheet eluted with 40% ether in petroleum ether. For development of ozonide and peroxide spots, 3% KI in 1% aqueous acetic acid spray was better than iodine. The spots (of iodine) faded, but a permanent record was made by Xerox copying. Color of die spots varied from light brown (ozonide) to purple-brown (hydroperoxide), and the rate of development of this color was related to structure (diperoxide > hydroperoxide > ozonide). 2,4-Dinitrophenylhydrazine spray revealed aldehyde spots and also reacted with ozonides and hydroperoxides. Fractions were evaporated at room temperature or below in a rotary evaporator. 

The ozonide (4.3 grams) in ethyl acetate (25 ml.) was shaken with reduced platinum oxide (approximately 50 mg.) in a Burgess-Parr apparatus containing oxygen at 50 p.s.i.g. for 24 hours. The solution was aldehyde-free and gave a negative peroxide test. There was no detectable... 

The type of O2 adduct depends on the donor structure. For example, tetraphenyl-oxirane forms an ozonide (78), " 1,4-bifunctional radical cations form dioxanes (79) conjugated dienes form cyclic adducts (80) and ergosteryl acetate (81) forms the 5a,8fl-peroxide (82) at —78... 

The electronic perturbation at the carbon of the primary ozonide by a proximal acet-oxy group is that cycloreversion which gives rise to an intermediate with a more pronounced acceptor at the p position is disfavored. This effect is also manifested in 5-endo-acetoxynorborene, albeit in an attentuated fashion. 

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