scholarly journals Approaches to the synthesis of triterpenoids. IV. The ABC + E ring approach to the pentacyclic triterpene skeleton. Synthesis of a pentacyclic compound suitable for triterpene synthesis

1978 ◽  
Vol 56 (16) ◽  
pp. 2139-2149 ◽  
Author(s):  
John W. Apsimon ◽  
Satyanand Badripersaud ◽  
John W. Hooper ◽  
Richard Pike ◽  
George I. Birnbaum ◽  
...  
Keyword(s):  
Molecular Structure ◽  
Least Squares ◽  
Direct Methods ◽  
Unit Cell ◽  
Monoclinic Space Group ◽  
X Ray Diffraction ◽  
Pentacyclic Triterpene ◽  
X Ray ◽  
R Value ◽  
Triterpene Synthesis

Studies on the ABC + E ring construction of the pentacyclic triterpene skeleton are described. Acid-catalysed cyclisation of the mixture of diastereoisomers 11 led to preferential cyclisation of one isomer to 10-methoxy-2,2,4aβ,6aβ, 12bβ -pentamethyl-1,2,3,4,4a,5,6,6a, 6bα,7,8,12b,13,14-tetradecahydro-1-picenone (12). An X-ray analysis was performed on this compound which crystallizes in the monoclinic space group P2/c. There are four molecules in the unit cell which has dimensions a = 6.456(2), b = 42.518(6), c = 8.519(2) Å, β = 100.92(3)°. The structure was solved by direct methods and refined by block-diagonal least-squares to a final R value of 0.042 for all 3234 observed reflections. The molecular structure found by X-ray diffraction confirms the stereochemical reasoning used in the synthetic steps.

scholarly journals The reaction of 3,5-diphenyl-1,2-dithiolium-4-olate with aniline: the crystal structure of 1-phenylimino-2-phenylamino-3-phenylindene

1987 ◽  
Vol 65 (12) ◽  
pp. 2830-2833 ◽  
Author(s):  
David M. McKinnon ◽  
Peter D. Clark ◽  
Robert O. Martin ◽  
Louis T. J. Delbaere ◽  
J. Wilson Quail
Keyword(s):  
Molecular Structure ◽  
Crystal Structure ◽  
Single Crystal ◽  
Least Squares ◽  
Direct Methods ◽  
Monoclinic Space Group ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cell Dimensions ◽  
Unit Cell Dimensions

3,5-Diphenyl-1,2-dithiolium-4-olate (1) reacts with aniline to form 1-phenylimino-2-phenylamino-3-phenylindene (3a). Under suitable conditions, 6-phenylbenzo[b]indeno[1,2-e]-1,2-thiazine is also formed. These structures are confirmed by alternative syntheses. The molecular structure of 3a has been determined by single crystal X-ray diffraction. Compound 3a crystallizes in the monoclinic space group C2/c with unit cell dimensions a = 20.777(3) Å, b = 6.130(3) Å, c = 31.327(3) Å, 3 = 99.59(1)°, and Z = 8. The structure was solved by direct methods and refined by least squares to a final R = 0.055. The molecular structure of 3a shows the three phenyl containing substituents to have the planes of their ring systems tilted between 40° and 60° from the plane of the indene system due to steric repulsions.

The crystal structure of dibutyl-bis(pentamethylenedithiocarbamato)tin(IV)

1986 ◽  
Vol 51 (11) ◽  
pp. 2521-2527 ◽  
Author(s):  
Jan Lokaj ◽  
Eleonóra Kellö ◽  
Viktor Kettmann ◽  
Viktor Vrábel ◽  
Vladimír Rattay
Keyword(s):  
Molecular Structure ◽  
Crystal Structure ◽  
Least Squares ◽  
Coordination Polyhedron ◽  
Crystal And Molecular Structure ◽  
Distorted Octahedron ◽  
Monoclinic Space Group ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray

The crystal and molecular structure of SnBu2(pmdtc)2 has been solved by X-ray diffraction methods and refined by a block-diagonal least-squares procedure to R = 0.083 for 895 observed reflections. Monoclinic, space group C2, a = 19.893(6), b = 7.773(8), c = 12.947(8) . 10-10 m, β = 129.07(5)°, Z = 2, C20H38N2S4Sn. Measured and calculated densities are Dm = 1.38(2), Dc = 1.36 Mg m-3. Sn atom, placed on the twofold axes, is coordinated with four S atoms in the distances Sn-S 2.966(6) and 2.476(3) . 10-10 m. Coordination polyhedron is a strongly distorted octahedron. Ligand S2CN is planar.

Crystal and Molecular Structure of Dithiocyanato(triphenylarsine)mercury(II)

1975 ◽  
Vol 53 (22) ◽  
pp. 3383-3387 ◽  
Author(s):  
Joseph Hubert ◽  
André L. Beauchamp ◽  
Roland Rivest
Keyword(s):  
Molecular Structure ◽  
Least Squares ◽  
Coordination Number ◽  
Diffraction Data ◽  
Crystal And Molecular Structure ◽  
Heavy Atom ◽  
Monoclinic Space Group ◽  
X Ray Diffraction ◽  
X Ray ◽  
Heavy Atom Method

The crystal and molecular structure of dithiocyanato(triphenylarsine)mercury(II) has been determined from X-ray diffraction data. The crystals are monoclinic, space group P21/c, with a = 10.290(7), b = 21.199(23), c = 10.719(7) Å, β = 112.00(2)°, and Z = 4. The structure has been solved by the heavy-atom method and refined by block-diagonal least-squares calculations. The agreement factor R obtained for 2607 'observed' reflections is 0.030. The crystal consists of single molecules. The 'characteristic' coordination number of mercury is three, with two sulfur and one arsenic atoms at the apexes of a triangle. The nitrogen atoms of the thiocyanate groups are at 2.67 and 2.74 Å from the adjoining mercury atoms and therefore link the different molecules together.

The crystal and molecular structure of 1,4-diphenyl-2,2′,3,3′,5,5′,6,6′-octamethylcyclo-1,4-diphospha-2,3,5,6-tetrasilahexane, a phosphorus–silicon heterocycle

1979 ◽  
Vol 57 (2) ◽  
pp. 174-179 ◽  
Author(s):  
A. Wallace Cordes ◽  
Paul F. Schubert ◽  
Richard T. Oakley
Keyword(s):  
Molecular Structure ◽  
Crystal And Molecular Structure ◽  
Direct Methods ◽  
Chair Conformation ◽  
Monoclinic Space Group ◽  
Single Bond ◽  
X Ray Diffraction ◽  
Full Matrix ◽  
X Ray ◽  
Bond Lengths

The crystal structure of 1,4-diphenyl-2,2′,3,3′,5,5′,6,6′-octamethylcyclo-1,4-diphospha-2,3,5,6-tetrasilahexane, (PhPSi2Me4)2, has been determined by single crystal X-ray diffraction. The crystals are monoclinic, space group P21/c, with a = 9.866(1), b = 11.921(1), and c = 11.324(2) Å, β = 104.31(1)°, Z = 2, and ρcalcd = 1.15 g/cm3. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to a final R of 0.060 and Rw of 0.078, for 1173 reflections with intensities greater than 3σ. The (PhPSi2Me4)2 molecule lies on a crystallographic centre of symmetry, and the six-membered P2Si4 ring has a chair conformation with equatorial phenyl groups. The endocyclic angles at P (104.4(1)°) and Si (104.9(2)°) are intermediate between those found in cyclic hexaphosphine and hexasilane molecules, and the Si—Si and P—Si distances of 2.345(3) and 2.252(4) Å, respectively, correspond to single bond lengths, with no appreciable evidence for secondary pπ → dπ bonding between phosphorus and silicon. The Si—C (1.867(8) Å) and P—C (1.828(7) Å) bond lengths are also normal. The variations in the Si—P—C (101.6(2)°, 108.6(2)°), P—Si—C (range 106.2(3)–120.0(3)°), and Si—Si—C (range 105.8(3)–113.7(3)°) angles indicate that the positions of the exocyclic methyl and phenyl groups are influenced by both intra- and intermolecular steric forces.

The crystal and molecular structure of a platinum-silatrane complex

1977 ◽  
Vol 30 (5) ◽  
pp. 1007 ◽  
Author(s):  
GR Scollary
Keyword(s):  
Molecular Structure ◽  
Structural Analysis ◽  
Least Squares ◽  
Crystal And Molecular Structure ◽  
Monoclinic Space Group ◽  
X Ray Diffraction ◽  
Full Matrix ◽  
Space Group ◽  
X Ray

A structural analysis of the platinum-silatrane complex, PtCl [Si(OCH2CH2)3N] [PMe2Ph]2, has been carried out by X-ray diffraction. Crystals are monoclinic, space group P21/c, a 6.630(4), b 17.465(6), c 22.297(6) Ǻ, β 97.4(2)�, Z 4. The structure has been refined by a full- matrix least-squares procedure to R 0.048 for 2165 reflections. Basic geometries are square (platinum), tetrahedral (silicon) and trigonal (nitrogen). Within the silatrane ligand, the Si-N non-bonding distance is 2.89(1) Ǻ.

Studies of β-Diketone Complexes of Rhenium. VI. The Crystal and Molecular Structure of cis-Dichloropentane-2,4-dionato-trans-bis(triphenylphosphine)rhenium(III)

1974 ◽  
Vol 52 (9) ◽  
pp. 1704-1708 ◽  
Author(s):  
I. D. Brown ◽  
C. J. L. Lock ◽  
Che'ng Wan
Keyword(s):  
Molecular Structure ◽  
Single Crystal ◽  
Least Squares ◽  
Crystal And Molecular Structure ◽  
Unit Cell ◽  
X Ray Diffraction ◽  
Rhenium Atom ◽  
Full Matrix ◽  
X Ray ◽  
Nearest Neighbours

A compound, obtained in large yields from the reaction of acetylacetone and oxodichloroethoxobis(triphenylphosphine)rhenium(V) in benzene, has been shown by single crystal X-ray diffraction to be cis-dichloropentane-2,4-dionato-trans-bis(triphenylphosphine)rhenium(III). The crystals are monoclinic with a = 13.06(1), b = 18.30(1), c = 16.55(1) Å, and β = 112.7(2)°. The space group is P21/c and there are four molecules per unit cell. A total of 3841 independent reflections, of which 2686 were observed, were examined by film methods, the intensities being measured with a microdensitometer. The structure was refined by full matrix least-squares analysis to an R2 value of 0.068. The ligands are arranged around the rhenium atom in the manner described by the compound name to give a rough octahedron of nearest neighbours and the Re—Cl (2.369 Å av.), Re—O (2.02 Å av.), and Re—P (2.474 Å av.) distances are as expected.

The reaction of tetrasulphur dinitride with norbornadiene; the crystal and molecular structure of S4N2•C7H8, an eight-membered C2S4N2 heterocycle

1983 ◽  
Vol 61 (6) ◽  
pp. 1185-1188 ◽  
Author(s):  
Hans Koenig ◽  
Richard T. Oakley ◽  
A. Wallace Cordes ◽  
Mark C. Noble
Keyword(s):  
Molecular Structure ◽  
Least Squares ◽  
Dihedral Angle ◽  
Crystal And Molecular Structure ◽  
Direct Methods ◽  
Crystallographic Analysis ◽  
Monoclinic Space Group ◽  
Full Matrix ◽  
Space Group ◽  
X Ray

The reaction of tetrasulphur dinitride with norbornadiene produces the 1:1 adduct S4N2•C7H8; X-ray crystallographic analysis of this compound reveals that olefin addition cleaves one of the sulphur–sulphur bonds of S4N2, yielding a novel eight-membered C2S4N2 ring. Crystals of S4N2•C7H8 are monoclinic, space group P21/c, a = 6.127(1), b = 17.369(1), c = 9.580(1) Å, β = 106.74(1)°, V = 1003.8(5) Å3Z = 4. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.039. The S—S—N—S—N—S fragment of the C2S4N2 ring is planar to within 0.15 Å. The S—C—C—S unit is folded out of this plane to produce a dihedral angle of 74.5°.

Synthesis, conformational analysis, and molecular structure of 5-ethyl-5,6-dihydro-11H-dibenzo[b,e]azepine-6-thione

1994 ◽  
Vol 72 (2) ◽  
pp. 334-338 ◽  
Author(s):  
J. Irurre ◽  
F. Marquillas ◽  
A. Alvarez-Larena ◽  
J.F. Piniella
Keyword(s):  
Molecular Structure ◽  
Solid State ◽  
Conformational Analysis ◽  
Activation Barrier ◽  
Direct Methods ◽  
Membered Ring ◽  
Boat Conformation ◽  
X Ray Diffraction ◽  
X Ray ◽  
R Value

5-Ethyl-5,6-dihydro-11H-dibenzo[b,e]azepine-6-thione has been synthesized and studied in the solid state and in solution by X-ray diffraction and 1H DNMR, respectively. The crystals are monoclinic, P21/n, a = 9.642(1), b = 13.757(2), c = 9.889((2) Å, β = 98.57(1)°, Z = 4. The structure has been solved by direct methods and refined to an R value of 0.040 for 1771 reflections with I > 2.5σ(I). The seven-membered ring has a slightly deformed boat conformation. The activation barrier associated with the inversion ring has been determined, being ΔG≠ = 21.6 kcal/mol.

The crystal and molecular structure of dipyrrolidylthiuram disulfide

1983 ◽  
Vol 36 (7) ◽  
pp. 1371 ◽  
Author(s):  
GA Williams ◽  
JR Statham ◽  
AH White
Keyword(s):  
Molecular Structure ◽  
Crystal Structure ◽  
Single Crystal ◽  
Least Squares ◽  
Dihedral Angle ◽  
Crystal And Molecular Structure ◽  
Structural Parameters ◽  
Monoclinic Space Group ◽  
X Ray Diffraction ◽  
X Ray

The crystal structure of dipyrrolidylthiuram disulfide has been determined by single-crystal X-ray diffraction techniques at 295 K. Crystals are monoclinic, space group C2/c, unit cell a 13.835(3), b 10.422(2), c 9.427(3) �, β 97.08(2)� and Z 4. Automatic diffractometry has provided significant Bragg intensities for 1402 independent reflections, and the structure has been refined by least-squares methods to R 0.037. The structure consists of discrete C4H8NC(S)S2C(S)NC4H8 molecules. Half of each molecule is crystallographically unique with distances S-S 2.002(1), and C-S 1.804(2) and 1.645(2) �. The dihedral angle between planar C2NC(S)S portions is 87.9�. The relevance of the derived structural parameters to the question of why the tris(pyrrolidine-1-carbodithioato)iron(III) complex is, uniquely, high spin is discussed.

Studies of Rhenium β-Diketone Complexes. III. The Crystal and Molecular Structure of Bis(μ-O-1,3-diphenylpropane-1,3-dionatotricarbonylrhenium(I))

1973 ◽  
Vol 51 (2) ◽  
pp. 317-323 ◽  
Author(s):  
J. C. Barrick ◽  
M. Fredette ◽  
C. J. L. Lock
Keyword(s):  
Molecular Structure ◽  
Single Crystal ◽  
Least Squares ◽  
Main Part ◽  
Crystal And Molecular Structure ◽  
Unit Cell ◽  
The Other ◽  
X Ray Diffraction ◽  
Rhenium Atom ◽  
X Ray

One of a series of compounds obtained by the reaction of chloropentacarbonylrhenium(I) with β-diketones has been shown by single crystal X-ray diffraction to be bis(μ-O-1,3-diphenylpropane-1,3-dionatotricarbonylrhenium(I)). The crystals are monoclinic with lattice parameters a = 11.988(A) Å, b = 14.441(9) Å, c = 10.298(7) Å, β = 115.25(7)°. The space group is P21/c and there are two dimers per unit cell. A total of 1563 independent reflections were measured on a single crystal X-ray diffractometer and the structure was refined by least squares analysis to a weighted R2 value of 0.0427. The dimer units are held together by two bridging oxygen atoms, one from each of the β-ketoenolate groups; the distance of the bridging oxygen from the rhenium atom to which it is chelated (2.162(9) Å) is shorter than the distance to the other rhenium atom (2.204(7) Å). The main part of the β-ketoenolate ring is 37° from the OReO plane.

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