In 6-(3,4,5-trimethoxyphenyl)-6,7-dihydro-5H-1,3-dioxolo[4,5-g]quinolin-8(5H)-one, C(19)H(19)NO(6), (I), the six-membered heterocyclic ring adopts a conformation intermediate between envelope and half-chair forms; it is disordered over two enantiomeric configurations, with occupancies of 0.879 (3) and 0.121 (3), leading to positional disorder of the 3,4,5-trimethoxyphenyl unit. In 6-(1,3-benzodioxol-5-yl)-6,7-dihydro-5H-1,3-dioxolo[4,5-g]quinolin-8-one, C(17)H(13)NO(5), (II), the molecules are similarly disordered, with occupancies of 0.866 (4) and 0.134 (4). The molecules in (I) are linked by one three-centre N-H...(O)(2) hydrogen bond and one two-centre C-H...O hydrogen bond to form a complex chain of rings whose formation is reinforced by two independent aromatic pi-pi stacking interactions. In (II), a single N-H...O hydrogen bond links the molecules into a simple chain, and pairs of chains are linked by a single aromatic pi-pi stacking interaction.