Photooxygenation of Silyl Ketene Acetals: Dioxetanes as Precursors to α-Silylperoxy Esters in the Silatropic Ene Reaction

Article abstract of DOI:10.1021/jo00015a030

Photooxygenation of silyl ketene acetals afforded dioxetanes, which subsequently underwent secondary reactions to give rearrangement products (α-silylperoxy esters, major products) and cleavage products (pivalaldehyde, minor product).The kinetics of these reactions were studied by NMR and chemiluminescence.The activation energy of the chemiluminescence cleavage process was 2-3 kcal/mol higher than that of the rearrangement.In the presence of catalytic amounts of CF3COCF3 or CF3COCH3, the (E)-silyl ketene acetals rearranged into their Z isomers.Photooxygenation of the (E)- and (Z)-silyl ketene acetals showed that the <2+2> cycloaddition was rigorously diastereoselective.Trapping experiments with acetaldehyde confirmed the intermediacy of 1,4-zwitterions in the rearrangement of the (E)- and (Z)-dioxetanes into α-silylperoxy esters, but such intermediates were not detected during the photooxygenation of the silyl ketene acetals; the latter proceeds presumably via perepoxides.