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 derivative s 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-Methox ybenciliden)-2,2-dimethyl-1,3-dioxane-4,6-dione (3b). The structure of 3a w as refined to R-1 = 0.0421 for 2148 reflections (with I > 2 sigma (I)). Cry stal data for 3a: C13H11NO6, orthorhombic, space group Pbca, a = 16.008(3), b = 6.137(1), c = 25.281(5) Angstrom, V = 2483.6(8) Angstrom (3), Z = 8. T he structure of 3b was refined to R-I = 0.0496 for 4681 reflections (with I > 2 sigma (I)). Crystal data for 3b: C14H14O5. triclinic, space group P1, a = 9.131(2), b = 9.922(2), c = 14.490(3)Angstrom, alpha = 85.076(6), beta = 84.80(3), gamma = 89.37(2)degrees, V = 1302.4(5) Angstrom (3), Z = 4. The results of crystallographic and molecular modeling (AM1) were compared. Th e molecules in the crystal are held together, in both compounds, by van der Waals forces and C-H . . .O hydrogen bond interactions.