title: Crystal structures and conformations of two Diels-Alder adduct derivatives: 1,8-bis-(thio-phen-2-yl)-14-oxa-tetra-cyclo-[6.5.1.0(2,7).0(9,13)]tetra-deca-2(7),3,5-trien-10-one and 1,8-diphenyl-14-oxa-tetra-cyclo[6.5.1.0(2,7).0(9,13)] tetra-deca-2,4,6-trien-10-one.
abstract: The title compounds, C21H16O2S2 (I) and C25H20O2 (II), are products of a tandem 'pincer' Diels-Alder reaction consisting of [2 + 2] cyclo-additions between benzo[c]furan and cyclo-penta-none. Each comprises a fused tetra-cyclic ring system containing two five-membered rings (in envelope conformations with the O atom as the flap) and six-membered rings (in boat conformations). In addition, two thio-phene rings in (I) and two phenyl rings in (II) are attached to the tetra-cyclic ring system. The cyclo-penta-none ring adopts a twisted conformation in (I) and an envelope conformation in (II). In (I), the thio-phene rings are positionally disordered over two sets of sites, with occupancy ratios of 0.901 (2):0.099 (2) and 0.666 (2):0.334 (2). In (II), the oxygen atom of the cyclo-penta-none ring is rotationally disordered over two sites with an occupancy ratio of 0.579 (4):0.421 (4). The mol-ecular structure of (I) is stabilized by an intra-molecular C-H⋯O hydrogen bond, which generates an S(7) ring motif. In the crystal, the mol-ecules are linked via weak C-H⋯O hydrogen bonds, which generate R (2) 2(16) ring motifs in (I) and C(8) chains in (II). In both structures, the crystal packing also features C-H⋯π inter-actions. The crystal studied of compound (I) was twinned by non-merohedry. The twin component is related by the twin law [-1 0 0 -0.101 1 -0.484 0 0 -1] operated by a twofold rotation axis parallel to the b axis. The structure of (I) was refined with a twin scale factor of 0.275 (2).
authors: Department of Physics, RKM Vivekananda College (Autonomous), Chennai 600 004, India.
authors: S
authors: S
authors: Gopinath
authors: Department of Physics, RKM Vivekananda College (Autonomous), Chennai 600 004, India.
authors: P
authors: P
authors: Narayanan
authors: Department of Physics, RKM Vivekananda College (Autonomous), Chennai 600 004, India.
authors: K
authors: K
authors: Sethusankar
authors: Department of Organic Chemistry, University of Madras, Guindy Campus, Chennai 600 025, India.
authors: Meganathan
authors: M
authors: Nandakumar
authors: Department of Organic Chemistry, University of Madras, Guindy Campus, Chennai 600 025, India.
authors: Arasambattu K
authors: AK
authors: Mohanakrishnan
keywords: C—H⋯π inter­actions; Diels–Alder adduct derivative; conformation; crystal structure; hydrogen bonding; non-merohedral twin; thio­phene