ELECTRON VERSUS HYDRIDE ION TRANSFER IN THE REDUCTION OF BETA-HALOGEN-SUBSTITUTED 1,2-DIOXETANES BY 1,4-DIHYDRONICOTINAMIDES

The 3-halo-substituted 1,2-dioxetane 1 was employed as mechanistic probe in the reaction with NADH model compounds, namely, three N-substituted 1,4-dihydronicotinamides and 9,10-dihydro-10-methylacridine (AcrH-2), to differentiate between the direct hydride ion transfer and the electron transfer (SET) mechanisms. While AcrH-2 led mostly to cleavage into carbonyl products, the nicotinamides reduced the dioxetane 1 to yield the epoxy alcohol 3 as the main product. Additionally, the diol 2, the cleavage product bromoacetone, and the dehalogenation product acetone were observed. The formation of 3 is interpreted in terms of direct hydride ion transfer from the nicotinamides to the dioxetane with subsequent bromide elimination of the intermediary alkoxide. The dehalogenation product acetone was taken as evidence for initial electron transfer.