Photoinduced benzylation of 1,4-dimethoxynaphthalene by benzyl halides

Abstract

Irradiation of 1,4-dimethoxynaphthalene (DMNH) in the presence of 4-substituted benzyl chlorides (X–C₆H₄CH₂Cl, X = H, Cl, CN OR NO₂) in either acetonitrile or benezene solution results in benzylation of DMNH, predominantly at position 2 and to a lesser extent on the unsubstitued ring. Steady-state and flash photolysis studies show that charge transfer between singlet excited DMNH and the chlorides is involved. The reaction occurs predominantly in-cage via concerted electron transfer and carbon-chlorine bond cleavage with X = H or Cl, while with X = NO₂ fragmentation of the benzyl chloride radical anion occurs out-of-cage, but the process in this case is much less efficient due to competing back electron transfer.