Oxygen, singlet with ketenes

Dioxetan-ones appear to be intermediates in the chemiluminescent reaction of singlet oxygen with ketenes, in the presence of fluorescers 81> ... 

Tetramethoxyethylene in ether at -70 °C treated with oxygen under irradiation in the presence of zinc tetraphenylporphyrin furnishes a 94% yield of 1,1,2,2-tetramethoxydioxetane [37], Chemically generated singlet oxygen converts substituted ketenes into a-peroxylactones (equation 67) 20],... 

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). 

Bis-silyl ketene acetals devoid of -protons undergo a clean silatropic ene reaction with singlet oxygen (see Sections 2.3.2.1,3.ii and 2.3.2.4.3.H) to generate the a-silylperoxy silyl ester quantitatively. Treatment with methanol affords the a-hydroperoxy acid, also quantitatively (Scheme 23). Hytkogenation over platinum reveals the a-hydroxy acid, once again, quantitatively. Despite diis encouragement the substrate limitation is severe. 

Electron-rich olefins, especially vinyl ethers, " ketene acetals, thioalkyl-substituted olefins,and enamines, " react readily with singlet oxygen to give dioxetane cleavage products. Under carefully controlled temperature conditions, the intermediary 1,2-dioxetanes can be isolated. The first 1,2-dioxetanes prepared in this manner were the cis and trans isomers (8a) and (8b), respectively (Eq. 14). 

D. Silylation - Ketene bis(trimethylsilyl)acetals result from treatment of acid dianions with chlorotrimethylsilane.58 59 Esters behave analogously.60 Silylated ketene acetals can react like acid dianion equivalents. For example, reaction with singlet oxygen was used to produce the first operoxylactone.61,62... 

These compounds have also been prepared more simply by reaction of triphenyl phosphite ozonide with the more readily available ketenes (equation II). The ozonide is known to generate singlet oxygen, which reacts with the ketene to form an intermediate that collapses to the a-peroxylactone. ... 

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