A polarized, twisted, ethylene: structure of methyl 2-(1,3-dimethyl-2-imidazolidinylidene)-3-oxobutyrate dihydrate, C10H16N2O3.2H2O

Mr = 248, monoclinic, P21/n, a = 12.028 (2), b=7.168(2), c= 15.187(5)A, fl=91.88(2) °, Z= 4, V= 1308.6,~3, Din= 1.26, Dx= 1.263 Mgm -3, 2 (Cu Ka) = 1.5418 .A, g = 0.86 mm -1, F(000) = 536, T= 293 K. Final R = 5.6% for 2120 observed reflexions. Owing to the push-pull effect, the C=C bond distance is as long as 1.464 (2)/k with the twist angle about the bond 62.6.

Enantiospecific synthesis of tricyclo5.2.1.0(4,8)]decanes via acid catalysed rearrangement of isotwistanes

An acid catalysed rearrangement was employed for the enantiospecific conversion of isotwistanol to tricyclo5.2.1.0(4.8)]-decanes, which provided support for the proposed biosynthesis of allopupukeananes from pupukeananes. The strategy has been further extended to the enantiospecific synthesis of a homobrexane. (c) 2005 Elsevier Ltd. All rights reserved.

Exploring the Crystal Structure Landscape with a Heterosynthon Module: Fluorobenzoic Acid:1,2-Bis(4-pyridyl)ethylene 2:1 Cocrystals

The crystal structure landscape of the 2:1 benzoic acid:dipyridylethylene cocrystal (BA:DPE-I) is explored experimentally with fluoro-substituted benzoic acids and extended with studies employing the Cambridge Structural Database (CSD). The interpretation of the cocrystal landscape is facilitated by considering the kinetically favored and robust acidpyridine heterosynthon as a modular unit. Information based on high-throughput crystallography shows that polymorphs and pseudopolymorphs may belong to the same landscape but arise from different crystallization pathways because of complex and different kinetic features, and secondary synthon preferences. Using the CSD as a guide, the coformer was changed from 1,2-bis(4-pyridyl)ethylene (DPE-I) to 1,2-bis(4-pyridyl)ethane (DPE-II) and this provides an extended interpretation of the BA:DPE-I cocrystal landscape, also highlighting the complexity of the kineticthermodynamic dichotomy during the molecule-to-crystal progression.

Geometric quantum computation using fictitious spin-1/2 subspaces of strongly dipolar coupled nuclear spins

Geometric phases have been used in NMR to implement controlled phase shift gates for quantum-information processing, only in weakly coupled systems in which the individual spins can be identified as qubits. In this work, we implement controlled phase shift gates in strongly coupled systems by using nonadiabatic geometric phases, obtained by evolving the magnetization of fictitious spin-1/2 subspaces, over a closed loop on the Bloch sphere. The dynamical phase accumulated during the evolution of the subspaces is refocused by a spin echo pulse sequence and by setting the delay of transition selective pulses such that the evolution under the homonuclear coupling makes a complete 2 pi rotation. A detailed theoretical explanation of nonadiabatic geometric phases in NMR is given by using single transition operators. Controlled phase shift gates, two qubit Deutsch-Jozsa algorithm, and parity algorithm in a qubit-qutrit system have been implemented in various strongly dipolar coupled systems obtained by orienting the molecules in liquid crystal media.

Axial binding of 2-methylimidazole to the tetraarylcarboxylatodiruthenium (II, III) core: X-ray crystal structure of [Ru-2(O2CC6H4-p-OMe)(4)(2-mimH)(2)](ClO4). 1.75CH(2)Cl(2).H2O

Diruthenium (II. III) complexes of the type [Ru-2(O2CAr)(4) (2-mimH)(2)](ClO4) (Ar = C6H4-p-X : X=OMe,1, X=Me, 2, 2-mimH=2-methylimidazole) have been isolated from the reaction of Ru2Cl(O2CAr)(4) with 2-mimH in CH2Cl2 followed by the addition of NaClO4. The crystal structure of 1.1.75CH(2)Cl(2).H2O has been determined. The crystal belongs to the monoclinic space group p2(1)/c with the following unit cell dimensions for the C40H40N4O16ClRu2.1.75CH(2)Cl(2).H2O (M = 1237.0) : a = 12.347(3)Angstrom, b = 17.615(5)Angstrom, c = 26.148(2)Angstrom,beta = 92.88(1)degrees. v = 5679(2)Angstrom(3). Z=4, D-c = 1.45 g cm(-3). lambda(Mo-K-alpha) = 0.7107 Angstrom, mu(Mo-K-alpha) = 8.1 cm(-1), T = 293 K, R = 0.0815 (wR(2) = 0.2118) for 5834 reflections with 1 > 2 sigma(I). The complex has a tetracarboxylatodiruthenium (II, III) core and two axially bound 2-methylimidazole ligands. The Ru-Ru bond length is 2.290(1)Angstrom. The Ru-Ru bond order is 2.5 and the complex is three-electron paramagnetic. The complex shows an irreversible Ru-2(II,III)-->Ru-2(Il,II) reduction near -0.2 V vs SCE in CH2Cl2-0. 1 MTBAP. The complexes exemplify the first adduct of the tetracarboxylatodiruthenium (II,III) core having N-donor ligands

Bridged systems via radical cyclization reactions. Stereospecific synthesis of chiral tricyclo[6.2.1.0(1,5)]undecanes

The application of radical-mediated cyclizations and annulations in organic synthesis has grown in importance steadily over the years to reach the present status where they are now routinely used in the strategy-level planning.2 The presence of a quaternary carbon atom is frequently encountered in terpenoid natural products, and it often creates a synthetic challenge when two or more quaternary carbon atoms are present in a contiguous manner.3 Even though creation of a quaternary carbon atom by employing a tertiary radical is very facile, creation of a quaternary carbon atom (or a spiro carbon atom) via radical addition onto a fully substituted olefinic carbon atom is not that common but of synthetic importance. For example, the primary radical derived from the bromide 1 failed to cyclize to generate the two vicinal quaternary carbon atoms and resulted in only the reduced product 2.4 The tricyclic carbon framework tricyclo[6.2.1.01,5]undecane (3) is present in a number of sesquiterpenoids e.g. zizzanes, prelacinanes, etc.5

Studies in terpenoids. Part 42. Synthesis of 3-(2-hydroxyisopropyl)5,8-dimethyl-1,2-naphthoquinone (emmotin-H)

Emmotin-H, a naturally occurring sesquiterpenoid 1,2-naphthoquinone pigment (1) has been synthesised in a four step sequence starting from the known 5,8-dimethyl-4-oxotetralin-2-carboxylic acid (3a). Selenium dioxide oxidation of its methyl ester (3b) gives 3-methoxycarbonyl-5,8-dimethyl-1,2-naphthoquinone (4) which on reductive acetylation affords the corresponding diacetoxynaphthalene ester (5). Its reaction with excess of methylmagnesium iodide is accompanied by aerial oxidation during work-up and furnishes emmotin-H (1).

A 1h And 13c Magnetic Resonance And Infrared Spectroscopic Study Of Coordinated 2-Aminocyclopentene-1-Dithiocarboxylic Acid And Its S-Methyl Ester

The ligating properties of 2-aminocyclopentene-1-dithiocarboxylic acid and its S-methyl esters were investigated. Complexes with Zn(II), Cd(II) and Hg(II) halides were synthesized and characterized by infrared and proton and carbon-13 NMR studies. The results are concordant with a bidentate coordination of the -CS2 group to the metal ions

Lanthanide perchlorate complexes of 4-nitroquinoline-1-oxide and 5-nitroisoquinoline-2-oxide

Novel complexes of lanthanide perchlorates with 4-nitroquinoline-1-oxide (NQNO) and 5-nitroisoquinoline-2-oxide (NIQNO) have been prepared and characterized. The complexes have the general formulaeLn(NQNO)8(ClO4)3 (whereLn=La-Nd), Ln(NQNO)7(ClO4)3 (whereLn=Gd-Yb),Ln(NIQNO)9(ClO4)3 (whereLn=La-Nd), andLn(NIQNO)7(ClO4)3 (whereLn=Gd-Yb). The IR, proton NMR spectral data indicate the coordination of the N—O group of the ligands to he lanthanide ions.

Push-pull ethylenes: the structures of 3-(2-imidazolidinylidene)-2,4-pentanedione (I), C8H12N2O2, and 3-(1,3-dimethyl-2-imidazolidinylidene)-2,4-pentanedione trihydrate (II), C10H16N2O2.3H2O

(I): Mr= 168, triclinic, P1, Z=2, a= 5.596 (2), b = 6.938 (3), c = 10.852 (4) A, ~t= 75.64 (3), fl= 93.44 (3), ),= 95.47 (3) °, V= 406.0A 3, Din= 1.35 (by flotation using carbon tetrachloride and n-hexane), D x= 1.374 Mg m -3, g(Mo Kct, 2 = 0.7107 A) = 1.08 cm -l, _F(000) = 180, T= 293 K. (II): Mr= 250, triclinic, P1, Z= 2, a = 7.731(2), b=8.580(2), c=11.033(3)A, a= 97-66 (2), fl= 98.86 (2), y= 101.78 (2) °, V= 697.5 A 3, D m = 1.18 (by flotation using KI solution), Dx= 1.190Mgm -3, g(MoKa, 2=0.7107A)= 1.02 cm -1, F(000) = 272, T= 293 K. Both structures were solved by direct methods and refined to R = 4.4% for 901 reflexions for (I) and 5.7% for 2001 reflexions for (II). The C=C bond distances are 1.451 (3) A in (I) and 1.468 (3)A in (II), quite significantly longer than the C=C bond in ethylene [1.336 (2).~; Bartell, Roth, Hollowell, Kuchitsu & Young (1965). J. Chem. Phys. 42, 2683-2686]. The twist angle about the C=C bond in (II) is 72.9 (5) ° but molecule (I) is essentially planar, the twist angle being only 4.9 (5) ° .

Synthesis and Reactions of Binuclear Diolefin Rhodium(I) Compounds bridged by Nitrogen Heterocycles, Crystal Structure of Dichloro-Di-1,5-Cyclooctadiene(Mu-Pyrazine)-Dirhodium(I) [[Rh(1,5-C8h12)Cl]2(Mu-C4h4n2)]

Binuclear complexes of rhodium(I) of the type [(dien)(X)Rh(μ-N-N)Rh(X)(dien)] (dien = 1,5-cyclooctadiene or norbornadiene; N-N = pyrazine, 4,4′-bipyridine or Phenazine and X = Cl or Br) with bridging heterocycles have been isolated and their reactions with carbon monoxide, 2,2′-bipyridine and 1,10-phenanthroline investigated. The crystal structure of [(COD)(Cl)Rh(μ-pyrazine)Rh(Cl)(COD)] has been determined.

Structure of 7-methyl-1(2)a,1(6)a,3(4)a-trihomocubane-1(6)a,3(4)a-dione,star-c12h12o2- a case of enantiomeric and rotational disorder

M r = 188.22, monoclinic, P21/n, a = 6.219 (2), b= 10.508 (2), c=7.339 (1)A, t= 107.64 (2) °, V= 457 ,/k 3, Z = 2, D m - - 1.360 (3), D x = 1.366 (2)Mgm -3, ~,(MoKa) = 0.7107/~, #= 0.053 mm -I, F(000) = 200, T= 293 K. Final R = 5.8% for 614 significant reflections. The molecule, which does not possess a centre of symmetry, occupies a crystallographic centre of symmetry because of the statistical enantiomeric and rotational disorder. Latticeenergy calculations, based on van der Waals attractive and repulsive potentials, clearly show minima at the observed disordered positions.

Complexes Of Imidazoline-2-Thione And Its 1-Methyl Analogue With Cu(Ii), Zn(Ii), Cd(Ii) And Hg(Ii) Salts

The reaction of Cu(II), Zn(II), Cd(II) and Hg(II) chlorides and bromides with imidazoline-2-thione (IZT) and its N-methyl derivative (NMIZT) yields complexes of stoichiometry ML3X2 and ML2X (IZT) and its N-methyl derivative (NMIZT) yields complexes of stoichiometry ML3X2 and ML2X (where M=Cu(I)); copper(II) halides yield Cu(I) complexes. On the basis of infrared and 13C n.m.r.

Conformations Of Peptides Containing 1-Aminocyclohexane-Carboxylic Acid (Acc6) - Crystal-Structures Of 2 Model Peptides

The crystal structures of two peptides containing 1-aminocyclohexanecarboxylic acid (Acc6) are described. Boc-Aib-Acc6-NHMe · H2O adopts a β-turn conformation in the solid state, stabilized by an intramolecular 4 → 1 hydrogen bond between the Boc CO and methylamide NH groups. The backbone conformational angles (φAib = – 50.3°, ψAib = – 45.8°; φAcc6 = – 68.4°, ψAcc6 = – 15°) lie in between the values expected for ideal Type I or III β-turns. In Boc-Aib-Acc6-OMe, the Aib residue adopts a partially extended conformation (φAib = – 62.2°, ψAib = 143°) while the Acc6residue maintains a helical conformation (φAcc6 = 48°, ψAcc6= 42.6°). 1H n.m.r. studies in CDCl3 and (CD3)2SO suggest that Boc-Aib-Acc6-NHMe maintains the β-turn conformation in solution.

Structure of (6S,13bR)-1,2,3,5,6,13b-hexahydro-6-isopropyl-8H-pyrrolo[1',2':1,2]pyrazino[3,4,-b]quinazoline-5,8-dione

C17H19N302, monoclinic, P21, a = 5.382 (1), b = 17.534(4), c = 8.198(1)/L ,8 = 100.46(1) °, Z= 2, d,, = 1.323, dc= 1.299 Mg m-3, F(000) = 316, /~(Cu .Ka) = 0.618 mm -1. R = 0.052 for 1284 significant reflections. The proline-containing cispeptide unit which forms part of a six-membered ring deviates from perfect planarity. The torsion angle about the peptide bond is 3.0 (5) ° and the peptide bond length is 1.313 (5)A. The conformation of the proline ring is Cs-Cf~-endo. The crystal structure is stabilized by C-H... O interactions.