During our ongoing investigation of the phosphinite-directed C-C bond activation reactions 11 , we accidentally discovered that di-tert-butylphosphinite can serve as an effective DG to promote site-selective arene saturation (Fig. ). Phosphinite b1, easily prepared by the phosphinylation of polyaryl-substituted phenol a1, was employed as the model substrate. Using [Ru(p-cymene)Cl 2 ] 2 as the catalyst, the benzene ring adjacent to the phosphinite was selectively hydrogenated to a cyclohexyl ring with toluene and acetonitrile as co-solvents under 50 psi H 2 gas at 130℃ for 16 hours, which gave product c1 in 97% yield (94% isolated yield) after work-up with HCl (Fig. , entry 1). No hydrogenation of other aromatic rings in b1 was detected during this process. A series of control experiments were subsequently conducted. First, using other transition metals, such as Rh or Pd, instead of Ru gave no desired product (Fig. , entries 2 and 3). It is interesting to note that aromatic co-solvents are in fact compatible for this directed arene hydrogenation, further supporting the high chemoselectivity of this reaction. While the use of toluene is not critical, the absence of acetonitrile significantly decreased the yield (Fig. , entries 4 and 5). Lowering the hydrogen pressure to 20 psi or reducing the reaction temperature diminished the yield to some extent (Fig. , entries 6 and 7). Finally, the tert-butyl groups on the phosphinite DG proved to be essential, as less bulky substituents (e.g., isopropyl groups) were incompetent to provide the desired reactivity (Fig. , entry 8), though the exact reason remains to be uncovered.