Phosphite-ozone adducts

There is a continuing interest in the use of phosphite-ozone adducts as sources of singlet oxygen and as reagents for mimicking the reactions of this species. The commercially available phosphite (54) forms an ozone adduct of striking stability. Decomposition of the adduct only becomes appreciable at temperatures > 0 °C the decomposition exhibits first-order kinetics, so that at 10 °C= 9.10 x 10 min and= 76.2 min. These... 

Scheme 12.17 gives some examples of oxidations by singlet oxygen. The reaction in Entry 1 was used to demonstrate that 102 can be generated from H202 and CIO-. Similarly, the reaction in Entry 2 was used to verify that the phosphite-ozone adducts... 

Alkylidenetriphenylphosphoranes are oxidized by phosphite-ozone adducts.61 Ylides of the general structure (47) afford alkenes (R1 or R2 = H) or ketones (R1 or R2 H). N.m.r. evidence suggests that the former reaction proceeds via a quinquecovalent phosphorus intermediate (Scheme 13). 

The reaction of singlet oxygen with conjugated double bonds usually is a 1,4-cycloaddition leading to formation of derivatives of the 1,2-diox -ene ring system. This can be achieved either by photooxidation or by reaction in the presence of triphenyl phosphite-ozone adduct (Section Vin.D.2), shown in equations 85 and 86 . ... 

Alkylperoxy hydridosilane, preparation, 783 Alkyl phosphites, ozone adducts, 732 Alkyl sodium alkyl peroxide,... 

Arylidene-,6-ionones, triplet oxygen cycloaddition, 199, 201 Aryl phosphites, ozone adducts, 732 Aryl-substituted olefins, selenide-catalyzed epoxidation, 384-5 Ascaridole... 

Triaryl phosphite-ozone adducts, 706 Tri( -butyl)silyl peroxides, bis(trimethylsilyl) peroxide reactions, 796 Trichloroacetyl chloride, from tetrachloroethene, 731... 

A further simplification is obtained by the oxidative dimerization of the C20 phosphonium salt (45). The oxidation with molecular oxygen and with phosphite-ozone adducts was described by H. J. Bestmann and co-workers43 . The use of... 

Disconnect the gas inlet tube from the flask containing the phosphite-ozone adduct and replace it by a rubber septum. Connect the two flasks by a cannula and, while maintaining both at -78°C under nitrogen, add dropwise by means of applying a positive pressure of nitrogen, the phosphite-ozone solution through the cannula to the stirred solution of the ylide 89 over a period of 50 min. Maintain the mixture at -78°C for 1 h and then allow it to warm to room temperature. 

Such a process can produce 02( Ag) with 80% efficiency and similar reactions involving peroxide decomposition have been documented [21]. Of particular interest is the use of the decomposition of the endoperoxides of aromatic compounds, which, when appropriately substituted can be used in water [22] and of water soluble phosphite/ozone adducts [23]. Such chemical methods can provide a critical control for reactions in which photoexcitation of a sensitizer is suspected of doing more than just produce 02(1Ag). A prime example involves the rose bengal sensitized photooxidation of relatively unreactive alkenes [24],... 

The rather surprising observation has been made that gemacrene gives totally different products when it reacts with singlet oxygen, generated in a photosensitization reaction, than when it reacts with the triphenyl-phosphite-ozone adduct. There does not seem to be a clear-cut rationalization of this odd behaviour,... 

Anthryl ethers afford protection to alcohol functions treatment of the derivative with singlet oxygen, generated via the triphenyl phosphite-ozone adduct, followed by mild catalytic reduction, effects regeneration of the free alcohol (Scheme 136). 

Germacrene (318) reacts with the triphenyl phosphite-ozone adduct at —45°C at the 4,5-bond to give (319) after reduction, but with singlet oxygen initial attack occurs at the 7,13-bond, and further reaction gives the exocyclic... 

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