Boat-chair Conformation Research Articles

GEOMETRICAL OPTIMIZATIONS, NMR ANALYSES, AND NOVEL CRYSTAL STRUCTURES OF 3-OXA-7-BENZYL-7-AZABICYCLO[3.3.1]-NONAN-9-ONE AND 3-THIA-7-BENZYL-7-AZABICYCLO[3.3.1]-NONAN-9-ONE; STRUCTURAL ANALYSIS OF THE CORRESPONDING 3,7-DIHETERABICYCLO[3.3.l]NONANE HYDROPERCHLORATES

An investigation has been made of the structures of the title compounds via theoretical calculations, high resolution NMR analysis, and X-ray diffraction analysis. Conformational analyses of these compounds in the gas phase were performed using ab inito methods with GAUSSIAN 94. Single point calculations at the MP4/6-31G level for 3-oxa-7-azabicyclo[3.3.1]nonan-9-one revealed an energy difference of only ΔE = 1.497 kcal/mole between the chair-chair (CC) and boat-chair (BC) conformers. Full geometry optimization of the oxygen-containing ketone at the Hartree-Fock (HF) level using a 6-31G basis set indicated only a negligible variation in interatomic distances in the equilibrium geometry when the phenyl group was included in the calculation versus when the phenyl group was replaced by hydrogen. Full geometry optimization for the sulfur-containing ketone (phenyl replaced by a hydrogen) at the HF level using the 6-31G basis set again demonstrated that the BC form was slightly more stable than the CC form, identical to that found with the oxygen counterpart. Full geometry optimization of the two hydroperchlorates (phenyl replaced by hydrogen) resulted in the CC form being suggested as the more stable with H-bonding between the hydrogen on nitrogen and the respective heteroatom, a situation which likely enhances stability. Proton NMR analyses of both compounds using NOESY techniques strongly supported a predominance of the BC form in solution for the oxygen-containing ketone. Severe signal overlap in the sulfur ketone (even at 600 MHz) prevented in depth analysis of the structure. Using NOESY, DQCOSY, and HMBC techniques, NMR analyses of the corresponding hydroperchlorates implied CC forms for each in solution. The X-ray diffraction analysis of the oxygen-containing ketone revealed a CC in the solid state.

4-Heptamethyleneimino-7-nitrobenzo-2-oxa-1,3-diazole

The title compound, C 13 H 16 N 4 O 3 , crystallized in the P1 (No. 2) space group from ethyl acetate. The asymmetric unit contains two molecules with similar geometry. The cyclic amino moieties of the two independent molecules are in the boat-chair conformation and the amino-N atom is not in the plane of the aromatic ring. The bond distance between the amino N and the attached C atom of the 7-nitrobenzofurazan system is shorter than a normal C-N single bond. The other C-N bond, Which connects the nitro group with the ring, is also shorter than usual.

1,5-Bis(2-pyridylmethyl-N)-1,5-diazacyclooctane-N,N']chloronickel(II) perchlorate

The structure of the title compound, [NiCl(C 18 H 24 N 4 )]ClO 4 , is comprised of discrete [NiCl(C 18 H 24 N 4 )] + cations and perchlorate anions. The Ni II atom is five-coordinated by the four nitrogen donors of the new miniring macrocyclic ligand 1,5-bis(2-pyridylmethyl)-1,5-diazacyclooctane [Ni-N 2.074 (3)-2.108 (3) A], and by a chloride anion in the apical site [Ni-Cl 2.302 (1) A]. The coordination geometry of the complex could be considered as intermediate between square-pyramidal and trigonal-bipyramidal. The mini-ring macrocyclic ligand has a boat-chair conformation and the two pyridyl pendants are not coplanar.

The molecular structures of two melampolides

The melampolide-class sesquiterpene lactone 11βH,13-dihydro-14-hydroxy-(1,10)-cis-parthenolide, C15H22O4, 1, crystallizes in orthorhombic space group P212121 with a = 7.435(2), b = 12.678(2), c = 14.991(2) A, V = 1413.1(8) A3 and Z = 4. The aldehyde analog, C15H20O4·H2O, 2, crystallizes as the monohydrate in orthorhombic space group P212121 with a = 9.061(2), b = 9.295(2), c = 17.761(4) A, V = 1495.8(9) A3, and Z = 4. The 10-membered rings of the two molecules adopt approximate chair-boat conformations. In both compounds, the double bond at C1=C10 position of the cyclodecene ring is Z, while the C4=C5 is epoxidized with an E-configuration. The C15 methyl is β and H5 is α. The lactone ring is trans fused at the C6 and C7 positions to the 10-membered ring. The C13 methyl group has an α orientation in both molecules.

Synthesis, spectroscopic and structural studies on transition metal carbonyl complexes of cyclic di- and tetra-selenoether ligands

Reaction of [M(CO)4(nbd)] (M = Cr or Mo, nbd = norbornadiene) or [W(CO)4(TMPA)] (TMPA = N,N,N′,N′-tetramethyl-1,3-propanediamine) with [8]aneSe2 (1,5-diselenacyclooctane) yielded the cis-disubstituted tetracarbonyl species [M(CO)4([8]aneSe2)] (M=Cr, Mo or W). The complexes [M′X(CO)5] (M′=Mn, X=Cl, Br or I; M′=Re, X= Cl or Br) reacted similarly with [8]aneSe2 to give fac-[M′X(CO)3([8]aneSe2)] in high yield. Infrared and multinuclear NMR spectroscopic studies confirmed these assignments and indicated a single species in solution; δ(55Mn) lies in the same range as observed for other fac-[MnX(CO)3(diselenoether)] complexes, while for all of the compounds δ(77Se) is to low frequency of [8]aneSe2 itself (δ 137). Crystal structures of [W(CO)4([8]aneSe2)], [MnBr(CO)3([8]aneSe2)] and [ReBr(CO)3([8]aneSe2)] show the cyclic diselenoether chelating and adopting a chair-boat conformation. The compounds [16]aneSe4 (1,5,9,13-tetraselenacyclohexadecane) and L (1,6-diselena-3,4-benzocyclononane) reacted with the metal(II) species [{MoBr2(CO)4)}2] or [MI2(CO)3(NCMe)2] in CH2Cl2 solution to give seven-co-ordinate [{MoX2(CO)3}2([16]aneSe4)], [WI2(CO)3([16]aneSe4)], [MoX2(CO)3(L)] and [WI2(CO)3(L)], although these species decompose rapidly in co-ordinating solvents. Reaction of [16]aneSe4 with two molar equivalents of [M′Cl(CO)5] yielded the dinuclear complex [{MnCl(CO)3}2([16]aneSe4)] (in which the tetraselenoether is thought to bind in a bidentate manner to each Mn) and the mononuclear complex [ReCl(CO)3([16]aneSe4)] (which is thought to involve bidentate ligation to [16]aneSe4 with two free Se donors). The cationic species fac-[Mn(CO)3(η3-[16]aneSe4)]CF3SO3 was generated by treatment of [MnCl(CO)5] with AgCF3SO3 in Me2CO followed by addition of [16]aneSe4.

2-Vinyl- trans-octahydro-1,3-benzoxazine: Cyclization and 1,3-dipolar cycloaddition of nitrile oxides

A study of the stereochemistry of the acid-catalyzed cyclization between (−)-8-tosylaminomenthol (derived from (+)-pulegone) and acrolein diethyl acetal afforded two novel chiral perhydro-1,3-benzoxazine isomers 4a and 4b. Catalyst type as well as the reaction conditions dramatically affected the isomeric ratio. An X-ray crystal structure of 4a established a chair-boat conformation. The usefulness of this auxiliary was demonstrated by highly diastereoselective (i.e. 90% de) 1,3-dipolar cycloadditions with nitrile oxides.

The Study of π–π Interaction in Layered [3.3]Orthocyclophanes. Charge-Transfer Complexes of [3.3]Orthocyclophanes with Tetracyanoethylene

Abstract Dibenzo[3.3]orthocyclophanes ([3.3]OCPs) with a bicyclo[4.4.1]undecane substructure form charge-transfer (C-T) complexes with tetracyanoethylene (TCNE). 3,4 : 8,9-Dibenzobicyclo[4.4.1]undecane (9) and its 11-methylene derivative 8 are flexible molecules and take a chair-boat conformation. Complexes 8- and 9-TCNE exhibit the absorption maximum at ca. 420 nm, which coincides with the value for the TCNE complex of o-xylene. On the other hand, acetal 5, methylcarbinol 6, and dimethylmethylene derivative 7 are rigid, layered [3.3]OCPs with stacked benzene rings. Compounds 5, 6, and 7 form a 1 : 1 complex with TCNE in solution. The absorption maxima of the complexes at ca. 500 nm suggest an enhanced C-T complexation due to a π–π through-space interaction in 5, 6, and 7. A 2 : 1 complex of rigid [3.3]OCP 7 with TCNE crystallized from dichloromethane, while OCP 8 gave a red crystalline 2 : 3 complex with TCNE. X-ray crystallographic analyses of these two complexes is given.

Gomisin N

The crystal structure of gomisin N (1,2,3,12-tetramethoxy-6,7-dimethyl- 10,11-methylenedioxy-5,6,7,8-tetrahydrodibenzo[a,c]cyclooctene, C23H28O6). The cyclooctene ring of the molecule has a twisted boat–chair conformation. The angle between the two phenyl rings is 60.6 (11)°.

Transition-metal complexes as alternatives to proteolytic enzymes. Regioselective cleavage of myoglobin by palladium(II) aqua complexes

The palladium(II) aqua complexes [Pd(H2O)4]2+, cis-[Pd(en)(H2O)2]2+, and cis-[Pd(dtco-OH)(H2O)2]2+ effect hydrolytic cleavage of horse myoglobin in aqueous solution. The conditions were optimized with the third complex. Its structure was determined by X-ray crystallographic analysis of its precursor, the square-planar complex cis-[Pd(dtco-OH)Cl2], in which the chelating ligand adopts a boat-chair conformation. A weak interaction between the hydroxyl group and the palladium(II) atom seems to improve the stability of the reagent. The yield of cleavage after a 24-h incubation at 60 °C increases from 39% to 85% as the pH decreases from 6.2 to 3.2. The protein fragments are separated by SDS-PAGE electrophoresis and HPLC separation methods, and identified by ESIMS and MALDI-TOF mass spectrometric methods and by determination of terminal amino-acid sequences. Most of the 13 cleavage sites are clustered around the methionine, arginine, and some of the histidine residues, whose side chains can bind to palladium(II). Cleavage tends to occur at the peptide bonds one to three positions removed from the binding residues; the scissile bonds usually lie on the amino-terminal side, seldom on the carboxy-terminal side, of the binding residues. Removal of the heme and unfolding of the protein do not drastically alter the pattern of cleavage. The ability of palladium(II) aqua complexes to cleave proteins at relatively few sites, with explicable selectivity, with good to very good yield, and in weakly acidic and nearly neutral solutions, bodes well for their future use in biochemical and bioanalytical practice.

Germacranolide fromTanacetopsis mucronata

A sesquiterpene lactone of the germacrane series, mucrochin, has been isolated from the epigeal part ofTanacetopsis mucronata, and its structure has been studied by IR and mass spectral methods and PMR spectroscopy. It structure has been determined unambiguously by x-ray structural analysis as 5,6-dihydroxy-5α,6β,7α,8β(H)-germacra-1(10),4(15) 1(13)-trien-8,12-olide. A boat-chair conformation with a configuration of the1D1415D5 type has been established.

Quantitative determination of conformational equilibria in 3,7-diazabicyclo[3.3.1]nonane derivatives

A method of quantitative determination of a conformational equilibrium in 3,7-diazabicyclo[3.3.1]nonane (bispidine) derivatives is described. It is based on a comparison of coupling constants J 1−2 β and others with the corresponding ones from the models of pure conformers. 3-Benzyl-7-methyl-3,7-diazabicyclo[3.3.1]-nonane ( 4) proved to exist mainly in a double-chair (CC) conformer, although there is also a significant contribution of chair-boat (CB) and boat-chair (BC) conformers. In 3-benzyl-7-methyl-3,7-diazabicyclo[3.3.1]nonan-9-one ( 5), a CB conformer predominates over significant amounts of BC and CC.

Theoretical study of structure and NMR properties of the ?-hydrido-bridged cyclodecyl cation and related systems

Full conformational analysis on the cyclodecyl cation was performed at the HF/6-31G** level of theory. The most stable conformer is established as having a boat–chair structure with a 1,5-transannular interaction and a symmetrical and bent μ-hydrido bridge, which involves a two-electron three-center bond. Similar boat–chair conformations are preferred by the homologous cyclooctyl and cyclononyl cations. For the related diaza- and diboracyclodecyl ions, the 1,6-transannular interaction in a cis-decalin-type geometry is more favorable than is the competing 1,5-process. These structural models are fully consistent with the main features observed in the NMR spectra. In particular, the unusual patterns of the chemical shifts and nuclear spin–spin coupling constants in the bridging backbones HtX(DOTTED BOND)Hμ(DOTTED BOND)XHt are also satisfactorily reproduced by the ab initio results obtained with the continuous-set-of-gauge-transformations and equations-of-motion methods, respectively. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 313–320, 1998

The molecular structures of two furanoheliangolides

The heliangolide-class sesquiterpene lactone 8β-angeloyloxy-9α-acetoxycalyculatolide, C22H26O8,1, crystallizes in orthorhombic space groupP212121 witha=12.455(3),b=12.601(3),c=14.023(5) A,V=2200(1)A,3 Z=4.R=0.059 for 1735 observed data. The 11,13-dihydro-11α, 13-epoxyatripliciolide-8β-angelate, C20H22O7. 1/2 H2O,2, crystallizes as the hemihydrate with two molecules in the asymmetric unit in triclinic space groupP1 witha=9.422(1),b=9.559(1),c=12.358(3) A, α=101.62(2)°, β=91.30(2)°, γ=117.80(1)°,V=955.6(7)A3,Z=2.R=0.046 for 3607 observed data. In both, the 10-membered rings adopt approximate chair-boat conformations. Their conformations are typical for heliangolides. The methyl group C14 is α, while the C-15 has a β-orientation. The α-methylene-γ-lactone istrans-fused at C6 and C7 with H6 β and H7 α. In compound2, the epoxide at C11–C13 has an α orientation.

Cyclic Aminophosphites and -phosphoranes Possessing Six- and Higher-Membered Rings: A Comparative Study of Structure and Reactivity.

Aminophosphoranes 2 and 4-9 with a cyclohexylamino substituent and ring sizes varying from five to eight have been synthesized by oxidative addition reactions of cyclic aminophosphites with diols or 1,2-diketones. The reactivities of these phosphoranes are compared with those of the corresponding cyclic aminophosphites. The difference in hydrolytic pathways between amino- and analogous phenoxyphosphoranes is discussed. X-ray structures of two sets of compounds, (a) (C(6)H(11)NH)P(OCH(2)CMe(2)CH(2)O) (1) and (C(6)H(11)NH)P(OCH(2)CMe(2)CH(2)O)(1,2-O(2)C(6)Cl(4)) (2) and (b) (C(6)H(11)NH)P{O-(t-Bu)(2)C(6)H(2))(2)CH(2)} (3) and (C(6)H(11)NH)P{(O-(t-Bu)(2)C(6)H(2))(2)CH(2)}(1,2-O(2)C(6)H(4)).(1)/(2)Et(2)O (4.(1)/(2)Et(2)O) have been determined and geometrical parameters compared between the P(III) and the corresponding P(V) compounds. In 1, the six-membered ring has a chair conformation with the amino group axial; in 2, the six-membered ring is located apical-equatorial in a trigonal bipyramidal geometry and has a boat conformation. The eight-membered ring has a boat-chair conformation in 3, whereas the same ring has a tub conformation in 4.

Structure of 2,10 dichloro 6-(2,3 dimethylphenoxy) dibenzo [d,g] [1,3,6,2]dioxathiaphosphocin 6-sulphide

Abstract 2,10 Dichloro 6-(2,3 dimethylphenoxy) dibenzo [d. g] [1,3.6,2] dioxathiaphosphocin 6-sulphide (C20H15Cl2O3PS) crystallizes in the triclinic system, P[unk] with a = 7.845(3) Å, b = 11.720(2) Å, c = 11.871(2) Å, a = 88.5(2)°, β = 73.6(2)°, γ = 89.1(2)°, V = 1046.7(4) Å3, Z = 2, D c = 1.489M gm−3, (MoKα ) = 0.71069 Å, F(000) = 480 and T = 293 K. The crystal structure was solved by direct methods and refined by full matrix least-squares method to a final R = 0.0345 for 2701 unique observed reflections [I ≥ 2σ(I)]. The chlorobenzene rings A & B which are at 68.8° to each other, are oriented respectively at 19.9° and 61.6° to the phenyl ring and both are at 36.5° to the best plane of the heterocyclic ring. The heterocyclic ring adopts a distorted boat chair conformation.

Synthesis, Conformational Analysis and Transannular Reactions of 5,9-Propanobenzo[7]annulene Derivatives

(5α,9α,11β)-11-Hydroxy-6,7,8,9-tetrahydro-5H-5,9-propanobenzo[7]annulen-7-one ethylene ketal (6a) and its 11α-methyl derivative (6b) were prepared from monoketal 3. These compounds underwent acid-catalyzed transannular reactions leading to 6,7,8,9-tetrahydro-5H-5,9-propanobenzo[7]annulene derivatives 5a, 8a and 5b, 8b, respectively, depending on the reaction conditions. The compounds 6a and 6b were dehydrated to 6,7,8,9-tetrahydro-5H-5,9-prop[1]enobenzo[7]annulen-7-one (9a) and its 11-methyl derivative (9b), respectively. The conformational analysis of the 5,9-propanobenzo[7]annulene derivatives by molecular mechanics calculations (MM3 program) and the 1H NMR data show that hydroxyketal 6a and the related compound (5α,7β,9α)-6,7,8,9-tetrahydro-5H-5,9-propanobenzo[7]annulen-7-ol (4) exist mainly in the boat-chair conformation with the boat cycloheptenol ring, while for hydroxyketal 6b the chair-boat conformation (chair cycloheptenol ring) seems to be the preferred one.

2-(1-Hydroxy-4,4-dimethyl-2-oxobutyl)-4-methoxy-1-naphtholactone

The crystal structure of the tricyclic keto lactone, C18H18O4, has been determined by X-ray diffraction. The eight-membered heterocyclic ring in the molecule displays a distorted boat conformation in contrast to the more favoured boat-chair conformation in various oxygen-containing eight-membered ring systems.

AM1 study of conformations of oxocane and 1,3-dioxocane

AM1 semi-empirical SCF MO calculations are reported for important conformations of oxocane (1) and 1,3-dioxocane (2). The boat-chair conformation of1 (BC-1) is found to be the most stable form, whereas the crown family conformation is calculated to be 3.7 kJ·mol−1 less stable. The boat-boat form of1 is 15.9 kJ·mol−1 less stable thanBC-1. The boat-chair conformation of2 (BC-1,3) is calculated to be the most stable form of 1,3-Dioxocane. The crown-family conformation and the boat-boat geometry of this compound are 4.2 and 8.3 kJ mol−1 less stable thanBC-1,3.

2,10-Dichloro-6-(2,4-dimethylphenoxy)dibenzo[d,g][1,3,6,2]dioxathiaphosphocine 6-Sulfide

In the crystal structure of the title compound, C 20 H 15 Cl 2 O 3 PS 2 , the dioxathiaphosphocine ring adopts a boat-chair conformation, with the phosphoryl sulfide group axial and the phenoxy group equatorial. The planar chlorobenzene groups fused to the heterocyclic ring form an angle of 67.90 (10)° with one another.

MEDIUM-SIZED GERMANIUM HETEROCYCLES: FIRST SYNTHESIS AND CONFORMATIONAL ANALYSIS OF A STERICALLY HINDERED EIGHT MEMBERED 12H-DIBENZO[d,g] [1,3,2]DIOXAGERMOCIN

Abstract The first reported synthesis, characterization, and conformational analysis of the eight-membered germocin 2,2′-(4,6-di-1BuC6H2O)2GeMe2 (3) is described. The VT 1H NMR, 13C(1H) NMR, and crystallographic data of 3 is consistent with a boat-chair conformation for the ring in both solution and the solid state. The free energy of activation (ΔG299∗) for ring inversion is 55.6 kJ · mole−1 (13.3 cal · mole−1).