Photooxygenation (1O2) of silyl enol ethers derived from indan-1-ones: competitive formation of tricyclic 3-siloxy-1,2-dioxetane and α-silylperoxy ketone

Abstract

Photooxygenation (¹O₂) of silyl enol ethers 1 (X = H) and 2 (X = OMe) derived from indan-1-ones has been investigated. The oxygenation of silyl enol ethers 1 (X = H) was found to give the corresponding tricyclic 3-siloxy-1,2-dioxetanes 3 quantitatively. Alternatively, the silyl enol ethers 2 (X = OMe) gave tricyclic dioxetanes 6 together with α-silylperoxy ketones 7. The substituent effects of X = OMe on the direct formation of α-silylperoxy ketone 7 are explained by the formation of the 1,4-zwitterion intermediates (ZI). Thermolysis of the tricyclic 3-siloxy-1,2-dioxetanes 3 and 6 was observed for the first time to yield the keto esters 4 and 8, respectively.