Ketene acetals singlet oxygen

Oxidation of Ketene Silyl Acetals. Singlet oxygen oxidizes KSAs resulting in a cleavage of C-C bonds (eq 16),4 the reaction presumably proceeding through a silyl peroxide intermediate. Lead(IV) acetate and m-chloroperbenzoic acid" oxidize KSAs to or-acetoxy (or hydroxy) carboxylic acid derivatives. Oxidative dimerization of ketene silyl acetals by TiCU (eq 17) can be understood in terms of single-electron transfer to the Lewis acids.4 ... 

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... 

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