Catalytic transformations of multifunctional molecules now offer access to a variety of useful intermediates. However, there are still some important unsolved problems. This is the case of the transformation of cyclic imides into lactams through selective monoreduction of one carbonyl group which is still a challenge in organic synthesis. Strong reducing reagents such as LiAlH 4 have been used to perform complete reduction with formation of cyclic amines, [1] and only in the special case of highly substituted cyclic acylureas (hydantoins) was the monoreduction into ureas obtained. [2] The monoreduction of phthalimides into isoindolinone derivatives has been performed in moderate to good yields under acidic conditions in the presence of stoichiometric amounts of reducing metals such as Sn [3] or Zn. [4] Their catalytic reduction in the presence of hydrogen has been carried out with Raney nickel as catalyst, but under drastic conditions (180 8C, 190 bar H 2 ). [5] In water, under hydrogen pressure at 100 8C, N-methylsuccinimide was transformed into 2-pyrrolidinone in the presence of water-soluble ruthenium precatalysts such as RuCl 3 β’3H 2 O, [RuCl 2 (dmso) 4 ], or [Ru(dmp)(H 2 O) 2 ](PF 6 ) 2 (dmp = 2,9-dimethylphenanthroline), but in modest yields (< 28 %). [6] Herein we report that the ruthenium precatalysts [RuCl 2 -(p-cymene)] 2 and [Ru 4 H 6 (p-cymene) 4 ]Cl 2 are efficient catalyst precursors for the monoreduction of cyclic imides in water under hydrogen pressure. Moreover, they make possible the concomitant monoreduction and hydrogenation of unsaturated cyclic imides into saturated lactams (Scheme 1). Scheme 1. [Ru] = [Ru 4 H 6 (p-cymene) 4 ]Cl 2 and [RuCl 2 (p-cymene)] 2 .