EVIDENCE FOR A 1,4-DIOXY DIRADICAL AS AN INTERMEDIATE IN THE THERMAL-DECOMPOSITION OF 3,3-DIBENZYL-1,2-DIOXETANE

The thermal decomposition of 3,3-dibenzyl-1,2-dioxetane (1) in CDCl3 and CH2Cl2 solutions afforded the expected decomposition product 1,3-diphenyl-2-propanone (2) and the novel rearrangement ketone 1-(benzyloxy)-3-phenyl-2-propanone (3) in ratios of (73 +/- 10):(27 +/- 10). A plausible mechanism for the formation of ketone 3 involves homolytic cleavage of the dioxetane peroxide bond with subsequent beta cleavage of the benzyl group in the 1,4-dioxy diradical and in-cage combination of the resulting radicals. Moreover, several control experiments render a benzyl radical-induced decomposition of dioxetane 1 unlikely. Thus, the ratio of 2 and 3 was found to be essentially independent of the initial dioxetane concentration, and the presence of radical scavengers did not affect the product ratio and reaction rate. With the electron-rich 1,4-dioxene, the dioxetane 1 afforded the cycloadduct cis-3,3-dibenzyl-2,5,7,10-tetraoxabicyclo[4.4.0]decane (4) as major product.