Central Six-membered Ring Research Articles

Crystal structure of (Z)-3-benz-yloxy-6-[(2-hy-droxy-5-methyl-anilino)methyl-idene]cyclo-hexa-2,4-dien-1-one.

In the title Schiff base compound, C21H19NO3, the conformation about the C=C bond is Z. The N—H group and carbonyl O atom form an intra­molecular N—H⋯O hydrogen bond with an S(6) ring motif. The benz­yloxy ring and the 2-hy­droxy-5-methyl­phenyl ring are inclined to the central six-membered ring by 13.68 (9) and 9.13 (8)°, respectively, and to one another by 21.95 (9)°. In the crystal, mol­ecules are linked by O—H⋯O hydrogen bonds, forming helical chains along [010].

5-Amino-5'-bromo-6-(4-methyl-benzo-yl)-8-nitro-2,3-di-hydro-1H-spiro-[imidazo[1,2-a]pyridine-7,3'-indolin]-2'-one including an unknown solvate.

In the title compound, C22H18BrN5O4, the central six-membered ring, derived from 1,4-di­hydro­pyridine, adopts a distorted boat conformation with a puckering amplitude of 0.197 (3) Å, the imidazole ring adopts a twisted conformation with a puckering amplitude of 0.113 (3) Å, and the oxindole moiety is planar with an r.m.s. deviation of 0.0125 Å. Two intra­molecular N—H⋯O hydrogen bonds are formed, each closing an S(6) loop. In the crystal, strong N—H⋯O hydrogen bonds lead to the formation of zigzag chains along the c axis. These are consolidated in the three-dimensional crystal packing by weak N—H⋯O hydrogen bonding, as well as by C—H⋯O, C—H⋯Br and C—H⋯π inter­actions. A small region of electron density well removed from the main mol­ecule was removed with the SQUEEZE procedure in PLATON [Spek (2009 ▶). Acta Cryst. D65, 148–155] following unsuccessful attempts to model it as a plausible solvent mol­ecule. The unit-cell characteristics do not take into account this feature of the structure.

Ethyl 2,6-bis-(4-chloro-phen-yl)-1-iso-cyano-4-oxo-cyclo-hexa-necarboxyl-ate.

In the title compound, C22H19Cl2NO3, the central six-membered ring is in a twist-boat conformation. The two aryl groups are in equatorial positions, trans to each other and with a dihedral angle of 77.50 (2)° between them. One of the least hindered –CH2– groups and one of the aryl-substituted C atoms, with its axial H atom, are in the flagpole positions. The eth­oxy­carbonyl group is in an equatorial position and is cis to the second aryl group. In the crystal, molecules are linked via weak C—H⋯O hydrogen bonds, forming chains along [010].

5-Amino-6-benzoyl-8-nitro-2,3-di-hydro-1H-spiro-[imidazo[1,2-a]pyridine-7,3'-indolin]-2'-one dimethyl sulfoxide monosolvate.

In the title compound C21H17N5O4·C2H6OS, the central six-membered ring derived from 1,4-di­hydro­pyridine adopts a distorted boat conformation with a small puckering amplitude of 0.127 (3) Å. The sums of bond angles around the pyridine N atom [358.7 (2)°] and the other imidazolidine N atom [60 (2)°] indicate that these atoms are in sp2 hybridization, leading to an essentially planar imidazolidine ring. The last heterocycle, an oxindole moiety, is also nearly planar with an r.m.s. deviation of 0.0185 (1) Å. The amine NH2 group forms an intra­molecular hydrogen bond with the benzoyl group, giving a S(6) motif. In the crystal, N—H⋯O hydrogen bonds lead to the formation of chains along the c-axis direction. Within the chains there are further N—H⋯O and C—H⋯O hydrogen bonds enclosing R 2 2(14) ring motifs. The chains are linked via N—H⋯O and C—H⋯O hydrogen bonds involving the dimethyl sulfoxide solvent mol­ecule which acts as both an acceptor and a donor..

Crystal and molecular structure of (5S,8aS,9S)-9-hydroxy- 5-methyl- 4,6,7,8,8a,9-hexahydrothieno-[ 3,2-f] indolizin-5-ium iodide

Abstract The title compound, C11H16NOS・I, is chiral molecule with three stereogenic centres. The absolute configuration was assigned from the synthesis and confirmed by the structure determination. The central six-membered ring of the indolizine moiety adopts a half-chair conformation with atom displaced by 0.655 (2) A from the plane of the oder remaining five atoms. The pyrrolidine ring adopts an envelope conformation, with the greatest deviation from the mean plane of the ring being 0.646 (2) A for the bridgehead N atom. The crystal structure of the title compound is stabilized by O-H・・・I and C-H・・・O hydrogen bonds.

(11aS)-1,5,11,11a-Tetrahydro-1-benzothieno[3,2-f]indolizin-3(2H)-one

The absolute configuration of the title compound, C14H13NOS, was assigned from the synthesis and confirmed by the structure determination. There are two independent mol­ecules in the asymmetric unit. The central six-membered ring of the indolizine moiety adopts an envelope conformation, with the greatest deviations from the mean planes being 0.569 (3) and 0.561 (3) Å for the indolizine bridgehead C atoms of the two mol­ecules. The benzothieno ring attached to the indolizine ring system is planar to within 0.015 (3) Å in both mol­ecules. In the crystal, weak C—H⋯O and C—H⋯π inter­actions lead to the formation of a three-dimensional framework structure.

Transannular Diels–Alder/1,3-Dipolar Cycloaddition Cascade of 1,3,4-Oxadiazoles: Total Synthesis of a Unique Set of Vinblastine Analogues

A powerful tandem [4 + 2]/[3 + 2] cycloaddition cascade of 1,3,4-oxadiazoles initiated by a transannular [4 + 2] cycloaddition is detailed. An impressive four rings, four carbon-carbon bonds, and six stereocenters are set on each site of the newly formed central six-membered ring in a cascade thermal reaction that proceeds at temperatures as low as 80 °C. The resulting cycloadducts provide the basis for the synthesis of unique analogues of vinblastine containing metabolically benign deep-seated cyclic modifications at the C3/C4 centers of the vindoline-derived subunit of the natural product.

Crystal, molecular and electron structure of (2R,3R,4aS,5S,7R,10aS,10bS)-5-ethyl- 2,3-dimethoxy-2,3,7-trimethyl-decahydro-2H- [1,4]dioxino[2,3-g]indolizin-7-ium iodide hydrate

Abstract The title compound, C17H32NO4I・H2O, is chiral molecule with seven stereogenic centres. The absolute configuration was assigned from the synthesis and confirmed by the structure determination. The central six-membered ring of the indolizine moiety and 1,4-dioxane ring adopt a chair conformation, with two atoms displaced by -0.530(3), 0.712(3) and -0.631(2), 0.602(2) Å, respectively, from the plane of the other four atoms. The conformation of the pyrrolidine ring is close to that of a envelope, with the flap atom displaced by -0.600(3) A from the plane through the remaining four atoms. The electron structure was calculated by the semiempirical quantum chemistry method PM3. The crystal structure of compound is stabilized by O-H・・・I and O-H・・・O hydrogen bonds.

5′′-(2-Fluorobenzylidene)-1′-(2-fluorophenyl)-1′′-methyl-1′,2′,3′,5′,6′,7′,8′,8a'-octahydrodispiro[acenaphthylene-1,3′-indolizine-2′,3′′-piperidine]-2,4′′(1H)-dione

In the title compound, C37H32F2N2O2, the central six-membered piperidine ring adopts a twisted half-chair conformation, with the N and methyl­ene C atoms deviating by −0.2875 (16) and 0.4965 (15) Å, respectively, from the mean plane defined by the other four atoms. The piperidine connected to the octa­hydro­indolizine ring is in a half-chair conformation. The five-membered pyrrole ring adopts a slightly twisted envelope conformation with the piperidine C atom as the flap atom. The F and H atoms of both fluoro­benzene rings are disordered, with occupancy factors of 0.941 (3):0.059 (3) and 0.863 (3):0.137 (3). The mol­ecular structure features some intra­molecular C—H⋯O inter­actions. In the crystal, a supra­molecular zigzag chain sustained by C—H⋯F inter­actions parallel to the c axis is formed, generating a C(12) graph-set motif.

2-Methyl-3-(10H-phenothiazin-10-yl)buta-1,3-diene-1,1,4,4-tetracarbonitrile

In the title compound, C21H11N5S, the pheno­thia­zine unit has a butterfly structure, and the central six-membered ring adopts a boat conformation. The dihedral angle between the benzene rings is 127.64 (6)°, which is smaller than those reported for similar compounds because of the steric repulsion between the pheno­thia­zine and its tetra­cyano-1,3-butadiene substituent. The di­cyano­vinyl groups are almost orthogonal to one another, making a dihedral angle of 80.58 (6)°. In the crystal, the mol­ecules are aligned along the b axis. Four kinds of weak C—H⋯N inter­actions are recognized, one of which connects the mol­ecules into a one-dimensional array and the remaining three link these arrays.

Structural, energetic, spectroscopic and QTAIM analyses of cation–π interactions involving mono- and bi-cyclic ring fused benzene systems

The effect of increasing the number of monocyclic six-membered rings or bicyclic rings of bicyclo[2.1.1]hexenyl fused to benzene on cation-π interactions involving alkali metal ions (Li(+), Na(+), and K(+)) has been investigated. The binding energy data at the B3LYP/6-311+G(2d,2p) level clearly indicate that the binding affinity of the metal ion with benzene is enhanced by increasing the number of rings fused irrespective of a monocyclic or a bicyclic ring. Calculated binding energies are in good agreement with the available experimental results. The binding strength of cations with ligands decreases in the order Li(+) > Na(+) > K(+). Our study establishes that trisannelation of bicyclo[2.1.1]hexene to benzene facilitates a very strong interaction between benzene and cations. Infrared (IR) frequencies and nuclear magnetic resonance (NMR) chemical shifts are shown to be valuable in characterizing cation-π interactions. The C-C bonds of the central six-membered rings are weakened due to metal ion binding. Based on the Quantum Theory of Atoms in Molecules (QTAIM), we have observed the presence of stabilizing H∙∙∙H interactions in two of the considered systems as opposed to the frequent description of these interactions as non-bonded repulsive interactions. Alkali metal ion binding with those two ligands slightly reduces the strength of such H∙∙∙H interactions.

1-(10H-phenothiazin-10-yl)ethanone

In the title compound, C14H11NOS, the phenothia­zine unit has a butterfly conformation and the central six-membered ring has a boat form. The fold angle between the benzene rings is 46.39 (7)°, which is larger than found in similar compounds, probably as a result of steric repulsion between the phenothia­zine fragment and the acetyl group.

(5S,11aS)-5-Hydroperoxy-1,5,11,11a-tetrahydro[1]benzothieno[3,2-f]indolizin-3(2H)-one

The absolute configuration of the title compound, C14H13NO3S, was assigned from the synthesis and confirmed by the structure determination. The central six-membered ring of the indolizine moiety adopts an envelope conformation, with the greatest deviation from the mean plane of the ring being 0.661 (2) Å for the bridgehead C atom. The benzothiene ring attached to the indolizine ring system is planar to within 0.008 (2) Å. In the crystal, mol­ecules form chains parallel to the b axis via O—H⋯O hydrogen bonds.

(8aR,9R)-9-Hy-droxy-7,8,8a,9-tetra-hydro-furo[3,2-f]indolizin-6(4H)-one.

The title compound, C10H11NO3, crystallizes with four independent mol­ecules in the asymmetric unit. Their geometries are very similar and corresponding bond distances are almost identical. The central six-membered ring of the indolizine moiety adopts a envelope conformation [the displacement of the flap atom (the C atom opposite the N atom) being 0.539 (2), 0.548 (3), 0.509 (3) and 0.544 (3) Å in the four molecules], while the conformation of the oxopyrrolidine ring is close to that of a flat envelope. The displacements of the non-fused C atom opposite the C=O group of the pyrrolidine ring of the four mol­ecules are 0.366 (3), 0.335 (3), 0.173 (3) and −0.310 (3) Å. In the crystal, O—H⋯O hydrogen bonds link the mol­ecules into chains, which run parallel to the c axis. The absolute configuration was assigned from the synthesis.

10-(Prop-1-yn-1-yl)-10H-phenothiazine

In the title compound, C15H11NS, the asymmetric unit comprises one half-mol­ecule; a mirror plane passes through the S atom, the ynamine fragment, the methyl C atom and one methyl H atom. The phenothia­zine moiety has a butterfly conformation and the central six-membered ring has a boat conformation. The dihedral angle between the benzene rings is 149.40 (4)°. The crystal structure is stabilized by van der Waals inter­actions.

10-(6-Hydroxyhexa-2,4-diyn-1-yl)-10H-phenothiazine 5-oxide

The title compound, C18H13NO2S, has two independent mol­ecules (A and B) with similar conformations in the asymmetric unit. Both phenothia­zine moieties have a butterfly structure [dihedral angles between benzene rings = 155.17 (7) and 161.71 (7)°, respectively], and the central six-membered rings have a boat form. In the crystal, the A and B mol­ecules stack alternately along the b axis. The A and B mol­ecules are linked by O—H⋯O=S hydrogen bonds, forming zigzag chains along [10-1].

(11R,12S)-16-Amino-tetra-cyclo-[6.6.2.0(2,7).0(9,14)]hexa-deca-2(7),3,5,9(14),10,12-hexaen-15-ol.

In the title compound, C16H15NO, the dihedral angle between the outer benzene rings is 51.88 (6)°, and each of the central six-membered rings has a boat conformation. The hy­droxy and amino groups are syn, and the hy­droxy H atom forms an intra­molecular O—H⋯N hydrogen bond. In the crystal, mol­ecules assemble via C—H⋯O and C—H⋯π inter­actions, consolidating a three-dimensional architecture.

(1R*,2S*,4S*,5R*)-Cyclohexane-1,2:4,5-tetracarboxylic dianhydride

The title compound, C10H8O6, a promising raw material to obtain colorless polyimides which are applied to microelectronic and optoelectronic devices, adopts a folded conformation in which the dihedral angle between the two anhydro rings is 55.15 (8)°. The central six-membered ring assumes a conformation inter­mediate between boat and twist-boat. In the crystal, mol­ecules are linked by weak C—H⋯O inter­actions, forming a layer parallel to the bc plane.

A DFT study for the structures and electronic spectra of 2,3-dihydropyridine-4-ones

The molecular structure and electronic spectra of eleven dihydropyridones were theoretically studied utilizing density functional (DFT) method. The structures were optimized using B3LYP/6-31G(d,p) level of theory. The conformations of the molecules were analyzed with respect to substituents. The central six-membered dihydropyridone ring adopted a half-chair conformation. The geometries did not differ significantly except for conformations of the phenyl or styryl substituents. The only substituents that affected the structure of the central ring are those which have conjugation overlap with the -C=C-C=O system within the ring. Dipole moments and natural charges were calculated and it was found that in most cases substitution leads to higher dipoles, and both methyl and phenyl substituents have the same effect on the atomic charge distribution leading to decrease the atomic charge on the substitution site. Wiberg bond indices were also calculated and used to analyze the substitution effect on the electronic properties of the molecules. It is concluded that substitution on atoms that are not a part of the N-C=C-C=O system have practically no effect on both structural and electronic properties of the molecules. The electronic spectra were also calculated using the ZINDO method. The predicted spectra are in good agreement with experimental spectra concerning the long wavelength absorption band. The electronic transitions were either pure HOMO to LUMO transitions or comprises components of HOMO to LUMO and other transitions like H-1 to L, H to L+2, H-1 to L+1, H-2 to L+1.

(4R,6S,7S,8S,8aS)-6-Ethyl-7,8-dihydroxy-4-methyl-1,2,3,5,6,7,8,8a-octahydroindolizin-4-ium iodide

The title compound, C11H22NO2 +·I−, is a chiral mol­ecule with five stereogenic centres. The absolute configuration was assigned from the synthesis and confirmed by the structure determination. The central six-membered ring of the indolizine system adopts a chair conformation, with two atoms displaced by −0.690 (2) and 0.550 (2) Å from the plane of the other four atoms. The conformation of the pyrrolidine ring is close to that of an envelope, with the flap atom displaced by 0.563 (2) Å from the plane of the remaining four atoms. In the crystal, there are two O—H⋯I hydrogen bonds.