Unexpected High Regioselectivity in Rh-Catalyzed Homogeneous Hydrogenation of Naphthylene Derivatives

A highly regioselective homogeneous hydrogenation of naphthalene derivatives has been successfully achieved using a biphosphine/rhodium catalytic system. This protocol enables selective reduction of the nonfunctionalized ring for diverse naphthene derivatives including naphthols, ethers, naphthylamines, naphthalenes, and esters, delivering partially saturated products in 39–99% yields. Notably, precise regiodiscrimination was achieved even for 2-methylnaphthalene with subtle methyl substitution. Mercury and PvPy (poly(4-vinylpyridine)) poisoning tests suggest that the reaction likely occurs in a homogeneous manner.