CRYSTAL STRUCTURE OF
TRANS-5,6-DIMETHYLTETRADEHYDROPYRAN-2,4-DIONE.
José Ronaldo R. Bastos(PG), Dennis Oliveira Imbroisi(PQ) , Mariano Alves Pereira(PQ), Carlos Alberto De Simone(PQ)(a) , Paulo T. de Sousa Jr(PQ)., Domingos T. Martins(PQ),(b) and Julio Zukerman –Schpector(PQ)(c).
(a) Departamento de Química, CCEN, UFAL, Maceió, AL. (b) Departamento de Quimica, UFMT, Cuiabá, MT . (c) Laboratório de Cristalografia, Estereodinâmica e Modelagem Molecular-Departamento de Química, UFSCar, São Carlos,SP.
Palavras-chave: d-lactone, X-ray crystallography, and stereochemistry.
The title compound was prepared by a sequence of simple and reliable reactions: preparation of the dianion of the ethyl-acetoacetate (NaH, n-butillithium, THF, -10°C), alkyllation with methyl iodide, another preparation of the dianion and reaction with acetaldehyde followed by ester hydrolysis (NaOH, H2O, 12h, RT) and lactonization in acidic medium (HCl, H2O, 2h, 0ºC).1 It was purified by silica gel chromatography using ethylacetate and hexane as less polar fraction.
The crystals for the X-ray diffraction study were grown by slow evaporation from CDCl3. The data were measured on an Enraf-Nonius CAD-4 diffractometer using q-2q scan technique, at room temperature, and graphite monochromated MoKa radiation. Cell parameters were refined by least-squares-method on the basis of 25, high angle, independent reflections. Data were collected up to q = 26º and corrected for Lorentz-polarization effects. Three standard reflections were measured throughout the experiment and showed no significant variation. The structure was solved by the Direct Method (SHELXS86).2 and difference Fourier syntheses and refined anisotropically by full-matrix least-squares on F2 (SHELXL97).3 H-atoms were located on stereochemical grounds and refined with fixed geometry, each riding on a carrier atom, with an isotropic displacement parameter equal to 1.5 (for methyl H atoms) or 1.2 (for the other H atoms) times the value of the equivalent isotropic displacement parameter of the atom to which they were attached. A final difference Fourier map showed no peaks of chemical significance. Drawing was done using ZORTEP.4
Fig.
1. Trans d-lactone.
Physics Date: C7H10O3, fw =142.15, melting point: 85º - 87º. IR (KBr): umax : 3375, 2997, 2984, 2942, 2886, 2688, 2587, 2550, 1626, 1598, 1501, 1452, 1384, 1326, 1298, 1233, 1049, 1005, e 826 cm-1. 1H NMR (400MHz, CDCl3): d 1,19 (3H, d, J = 7,25Hz); 1,53 (3H, d, J = 6,67Hz); 2,30-2,38 (1H, m); 3,44 (1H, d, J = 19,08Hz); 3,56 (1H, d, J = 19,08Hz) e 4,41-4,48 (1H, m). 13C NMR (100MHz, CDCl3): d 10,69; 19,04; 45,81; 48,57; 76,96; 167,05; 202,41. Monoclinic, P21/c, a = 7.427(1), b = 7.857(2), c = 14.874(3) Å, b = 103.17(2)°, V = 845.1(3) Å3 , Z = 4, F(000) = 304, Dx = 1.117g.cm-3 , l(MoKa) = 0.71073 Å, m = 0.087mm-1. S = 1.034, R1 = 0.0623 for 828 reflections with I>2s(I) and 123 refined parameters.
Discussion: The trans molecule presents static disorder could be satisfactorily described by a simple model postulating two different conformation, with C2 and C3 atoms occupying alternatively one of two positions. The SOF factor of that positions were refined constraining their sum to be equal 1.00. The disorder in this compound accounts for the low quality of the crystal data, but nevertheless the main objective of this study was obtained which was the determination of the conformations. Atoms O1 and C4 are –0.16(2) and –0.14(1) C, respectively, out the plane defined by other four atoms, C2-C3-C5-C6 with a torsion angle of[3.7(7)]º while the same angle for H2-C2-C3-H3 of 177.4º indicates the trans configuration. The lactone ring for this molecule assumes twisted boat conformation. The molecules are maintained joins through hydrogen bonds with water’s molecule. The distances and angles involved with hydrogen bonds are: H2O...O1W = 1.772; O2 - O1W = 2.585(4); O2 - H2O = 0.82Å; O2 - H2O...O1W = 171º; O1W - H1W = 1.01; H1W...O3(i) = 1.836; O1W...O3(i) = 2.753(4)Å; O1W - H1W...O3(i) = 149º; O1W - H2W = 1.09; H2W...O3(ii) =1.684; O1W...O3(ii) = 2.776(4) Å; O1W - H2W...O3(ii) 178º. {[i] = (x,1+y, z) ; [ii] = (2 - x, 0.5+y, 0.5 –z)}.
1) José Ronaldo R. Bastos, Dennis Oliveira Imbroisi, Paulo T. de Sousa Jr., Domingos T. Martins. SBQ 1999 Resumo QO-099. 2) SHELDRICK, G.M. (1990). SHELXS86. Program for the Solution of Crystal Structures. Acta Crystallogr. A46, 467 – 473. 3) SHELDRICK, G.M. (1997). SHELXL97. Program for the Refinement of Crystal Structures. University of Göttingen, Germany. 4) ZSOLNAY, L. (1995). ZORTEP. An Interactive Molecular Graphics Program. Univ. Of Heidelberg, Germany. UFAL, FAPESP