Reductive Photoallylation of Dimethyl Naphthalenedicarboxylates by Allyltrimethylsilane via a Single Electron Transfer

Abstract The photoreaction of dimethyl 1,4-naphthalenedicarboxylate (4) with allyltrimethylsilane (7) in acetonitrile–methanol gave reductive allylation products. The formation of the products is rationalized by a mechanism involving a single electron transfer from 7 to the singlet excited state of 4, an attack of the allyl radical (16) generated by a C–Si bond cleavage in the radical cation of 7 toward the radical anion of 4 to give an anionic intermediate, and protonation of the intermediate. The photoreaction of dimethyl 1,2-naphthalenedicarboxylate (2) with 7 gave reductive allylation products along with a cyclobutane, possibly by the secondary photoreaction of another reductive allylation product. The photoreactions of dimethyl 1,3-, 2,3-, and 2,6-naphthalenedicarboxylates (3, 5, and 6) with 7 gave cyclobutanes, possibly by the photoreactions of reductive allylation products. The values of the free-energy changes (ΔGet) associated with the single-electron transfer from 7 to the singlet excited states of 2—6 and the fluorescence quenching rate constant (kq) support the photochemical single-electron transfer mechanism. The attacking position of 16 toward the radical anions of 2—6 and the position of the protonation of anions resulting from an attack of 16 are discussed on the basis of the values of the spin densities of the radical anions of 2—6 obtained by MNDO calculations and the net atomic charges of the model anions.