Synthesis and crystal structures of three Schiff bases derived from 3-formyl­acetyl­acetone and benzyl-, tert-butyl- and (S)-methyl­benzyl­amine

Treatment of 3-formyl­acetyl­acetone with the amines benzyl­amine, tert-butyl­amine and (S)-methyl­benzyl­amine led to the formation of the corresponding Schiff bases 3-[(benzyl­amino)­methyl­idene]pentane-2,4-dione, C(13)H(15)NO(2) (1), 3-[(tert-butyl­amino)­methyl­idene]pentan-2,4-dione, C(10)H(17)NO(2) (2) and 3-{[(S)-benz­yl(meth­yl)amino]­methyl­idene}pentane-2,4-dione, C(14)H(17)NO(2) (3). The mol­ecules of all three compounds exist as enamine tautomers that contain a nearly planar amino-methyl­ene-pentane-2,4-dione core with a strong intra­molecular N—H⋯O hydrogen bridge. The R group attached to the enamine N atom has no significant influence on the bond lengths and angles of the amino-methyl­ene-pentane-2,4-dione core. The supra­molecular structures in 1–3 are mainly based on weak C—H⋯O hydrogen bonds.