The-reaction,of cyclic urea 1,3-dimethyl-2-liniclazolidinone with the aluminum(I)' compound NacNacAl (1) gives an unexpected adduct of urea with the isomerized aluminum(III) hydride NacNac'AIH(O=SIMe) (3). A related reaction of 1 with phosphine oxides results in cleavage of the P=O bond and formation of hydroxyl derivatives NacNac'Al(OH)(O=PR3) [R = Ph (5) and Et (6)]. Density functional theory calculations revealed that these reactions proceed via a bimolecular mechanism in which either the-basic aluminum(I) center or the transient Al=O species deprotonate the methyl group of the NacNac ligand.