Phosphite ozonides

Hydroperoxylation of silyl dienol ethers was effected by the in t7/ -generated reagent triphenyl phosphite ozonide (Equation 26). The yields are moderate and the products are always accompanied by the hydroxylated equivalents. The mechanism was studied and it was found that the oxygen attached to the carbon came from the central O of the ozonide <2001JOC3548>. 

Several ketenes have been converted into l,2-dioxetan-3-ones by reaction with triphenyl phosphite ozonide (77JA5836), and ketenimines form cyclic iminoperoxides with photochemi-cally generated singlet oxygen (Scheme 97) <79AG(E)788,80CC898). 

Reaction with aji-unsaturated ketones and lactonesThe reactivity of a,/ -enones to singlet oxygen depends on the conformation. Systems that exist in s-trans-conformations (e.g., A4-3-ketosteroids) react slowly if at all. However, s-cis-enones react readily. For example, (R)-( + )-pulegone (1) reacts to give the products 2-4. The same products are obtained by oxidation with triphenyl phosphite ozonide (3, 324 325). 

Triphenyl phosphite ozonide, 334 Unsaturated lactones a-Alkylidene-7-lactones Chloromethyldiphenylsilane Butenolides... 

An alternative method of formation, which can be used in organic solvents at low temperatures, involves the thermal decomposition of triethyl phosphite ozonide (Equation 28-10) ... 

Another source is derived from phosphite ozonides as in the reaction... 

Ketenes can be converted into l,2-dioxetan-3-ones using triphenyl phosphite ozonide (Scheme 24) <1977JA5836, 1980CC898>. The Kopecky method for the formation of 1,2-dioxetanes involves the dehydrohalogenation of -halo hydroperoxides and is promoted by the action of a base or a silver salt (Scheme 25) <1975CJC1103>. 

Another variant on this chemistry is the use of triphenyl phosphite ozonide as a source of singlet oxygen. This reagent mimics singlet oxygen in many of its reactions, and is easier to quantify. 

While the reaction of singlet oxygen with silyl enol ethers was governed by competing prototropic and silatropic ene processes (see Section 2.3.2.1.3.ii), the interaction with dienol ethers displays a different mode of reactivity. Singlet oxygen generated from triphenyl phosphite ozonide at low temperature... 

Triphenyl phosphite ozonide, (CtHsOjjPOj, which is obtained by ozonization of triphenyl phosphite in dichloromethane solution at -78 °C, decomposes to triphenyl phosphate and singlet oxygen [178]. As an oxidant, it converts the trimethylsilyl ethers of enols of a,p-unsaturated ketones into unsaturated hydroxy ketones [996]. 

Biadamantylene dissolved in methylene chloride at -78 °C and treated with a solution of triphenyl phosphite ozonide in the same solvent and subsequently with a mixture of methanol and pyridine gives biadamantylene dioxetane in 91% yield (equation 64). The dioxetane decomposes at 150 °C [1101]. 

A solution of 9.3 g (0.03 mol) of triphenyl phosphite in 100 mL of dichloro-methane is ozonized to form triphenyl phosphite ozonide. After the excess ozone is purged with nitrogen, a cold solution of 1.60 g (0.02 mol) of 1,3-cyclohexadiene in 45 mL of dichloromethane is added from a dropping funnel while the mixture is stirred by a stream of nitrogen and cooled with a dry-ice-acetone bath. After the removal of the bath, the mixture is allowed to warm to room temperature. The solution is concentrated on a rotary evaporator, and the residue is distilled at less than 0.1 mm of Hg in a short-path still to give 1.51 g (67.4%) of pale-yellow semisolid 3,6-endooxocyclohexene, which, after three recrystallizations from pentane, melts at 90-91 °C. 

The thermal generation of singlet oxygen from hydrogen peroxide and hypochlorite presumably involves the chloroperoxy anion other synthetically useful examples involve decomposition of phosphite ozonides or endoperox-ides, as indicated in Scheme 67 (cf. Murray, 1979). 

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