The scandium (III) catalysed condensation of silylketene thioacetals and pyridylthioacetals with imines in pure water was studied. The reaction of the phenylthioacetal derivatives brings always to β-aminoesters; the reaction of pyridylthioacetals leads to the stereoselective formation of β-lactams in organic solvents, while in the presence of a large amount of water affords β-amino amides in good yields. That represents a new, easy, one-pot catalytic synthesis in water of an interesting class of compounds, direct precursors of 1,3-diamino hydroxy compounds. The possibility of recovering and recycling the catalytic systems was also briefly investigated.