Selinidin:: Crystal structure generated by C-H•••O, C-H•••π and π-π interactions

The title compound, 9,10-dihydro-8,8-dimethyl-2-oxo-2H,8H-benzo[1,2-b:3,4-b']dipyran-9-yl-2-methyl-2-butenoate, C19H20O5, was isolated from the roots of Selinum vaginatum. The compound crystallizes into monoclinic space group P2 (1) with unit cell parameters: a = 12.830(2) angstrom, b = e9.041(1) angstrom, c = 14.983(1) angstrom, beta = 95.09(1)degrees, Z = 4. The crystal structure has been determined using direct methods and refined by full-matrix least-squares to a final R value of 0.0529 for 3142 observed reflections. There are two independent molecules, A and B, per asymmetric unit. In both the molecules, the coumarin nucleus is planar. However pronounced differences are observed in the conformation of dihydropyran ring which has a half-chair conformation with an 8 beta-9 alpha orientation in molecule A and is intermediate between half-chair and sofa in molecule B. Differences also occur in the conformation of the 2-methylbutenoyloxy side chain at C9 due to the different geometry of C-H center dot center dot center dot pi interactions in molecules A and B. Molecules A and B are connected by pi-pi interactions between their coumarin fragments forming dimers. The dimers interact through C-H center dot center dot center dot O and C-H center dot center dot center dot pi hydrogen bonds.