Co-host: The Chemical Society of Japan, The Chemical Society of Japan, Kyushu Branch, The Society of Synthetic Organic Chemistry, Japan (Cooperation)
Mechanism of photoinduced phenyl-rearrangement of phenacyl sulfonates (mesylate, tosylate, triflate) were investigated in TFE and MeCN by the aid of solvent effect, leaving group effect, effect of added trapping reagents and laser flash photolysis. The photosolvolyses of three phenacyl sulfonates in TFE afforded nucleophilic substitution product by solvent. Phenacyl tosylate additionally afforded phenacyl alcohol, which is obtained by the oxidation of phenacyl radical. These result indicates the intervention of phenacyl carbocation and radical in the photosolvolysis. The yields of phenyl rearranged product were increased in the photosolvolysis of phenacyl mesylate and triflate which afforded little amount of radical derived products, as well as in the photosolvolysis of phenacyl chloride that affords little nucleophilic substitution product. The result suggest that the phenyl rearrangement proceed through a intermediate that does not suffer nucleophilic solvent attack. The addition of azide to the photosolvolysis of phenacyl mesylate in TFE resulted in the decrease of nucleophilic substitution product yield, whereas the yield of phenyl-rearranged product was little affected. Addition of nitroxide, on the other hand, decreased the yield of phenyl-rearranged product, and phenacyl-nitroxide adduct was obtained in corresponding yield. These results indicate the photoinduced phenyl-rearrangement proceeds through phenacyl radical intermediate.
