Synthesis, crystal structure and molecular modeling (AM1) of two 5-arylidene derivatives of Meldrum's acid

The synthesis and structural characterization of two 5-Arylidene derivatives of Meldrum's acid (2,2-dimethyl-1,3-dioxane-4,6-dione) are described: 5-(4-Nitrobenciliden)-2,2-dimethyl-1,3-dioxane-4,6-dione (3a), and 5-(4-Methoxybenciliden)-2,2-dimethyl-1,3-dioxane-4,6-dione (3b). The structure of 3a was refined to R₁ = 0.0421 for 2148 reflections (with I > 2 (I)). Crystal data for 3a: C₁₃H₁₁NO₆, orthorhombic, space group Pbca, a = 16.008(3), b = 6.137(1), c = 25.281(5) Å, V = 2483.6(8) ų, Z = 8. The structure of 3b was refined to R₁ = 0.0496 for 4681 reflections (with I > 2(I)). Crystal data for 3b: C₁₄H₁₄O₅, triclinic, space group P1, a = 9.131(2), b = 9.922(2), c = 14.490(3)Å, = 85.076(6), = 84.80(3), = 89.37(2)°,V = 1302.4(5) ų, Z = 4. The results of crystallographic and molecular modeling (AM1) were compared. The molecules in the crystal are held together, in both compounds, by van der Waals forces and C—H···O hydrogen bond interactions.