We herein report that a vicinal diol, which is prepared by a photoinduced dimerization reaction of xanthone, functions as the reductant in a coupling reaction of two organyl halides in the dark. The sterically strained C(sp(3))-C(sp(3)) sigma-bond located in the center of the diol breaks to donate the electrons accommodated therein for the formation of a new C-C bond, with the parent xanthone being recovered and recycled for regeneration of the diol. The diol is marked by its preparative convenience and reusability in comparison with other reducing agents that have been employed in analogous reductive coupling reactions.