The anomeric effect in thio derivatives of benzocycloheptene

1992 ◽  
Vol 70 (10) ◽  
pp. 2650-2658 ◽  
Author(s):  
S. Désilets ◽  
M. St-Jacques
Keyword(s):  
Nmr Spectroscopy ◽  
Low Temperature ◽  
High Field ◽  
Chair Conformation ◽  
Anomeric Effect ◽  
Conformational Properties ◽  
Y Fragment ◽  
Derivatives Of ◽  
Twist Boat

The conformational properties of six thio derivatives of benzocycloheptene were studied by 1H and 13C high-field NMR spectroscopy in solution at low temperature. Both parent compounds 2 and 6, with sulfur at positions 3 and 1, respectively, were found to exist in the chair conformation. The 2-substituted derivatives of 2 (3: Y = OCH3 and 4: Y = Cl) revealed the presence of the Ca form only. In contrast, the 2-substituted derivatives of 6 (7: Y = OCH3 and 8: Y = Cl), with sulfur at position 1, showed mixtures of three conformers, namely Ca:Ce:TB (Ca = axial chair, Ce = equatorial chair, and TB = twist-boat), whose populations in CHF2Cl were, respectively, 93:5:2 and 85:12:3. The predominance of the Ca form in both series argues in favour of a strong anomeric effect in spite of the large departure from coplanarity (~35°) in the:—S—C—Y fragment of both 7 and 8. This noncoplanarity appears to weaken only slightly the n–σ* overlap characteristic of the endo-anomeric effect, contrary to earlier observations for the:—O—C—Y fragment in 5. The differences between the effects of O and S are discussed.

Nuclear magnetic resonance characterization of the ring conformations of monosubstituted derivatives of 1,3-dioxa-5,6-benzocycloheptene

1983 ◽  
Vol 61 (1) ◽  
pp. 109-115 ◽  
Author(s):  
R. St-Amour ◽  
M. St-Jacques
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Substituent Effects ◽  
Steric Effects ◽  
Slow Exchange ◽  
Conformational Properties ◽  
Derivatives Of ◽  
Ring Conformations ◽  
Twist Boat

The conformational properties of 2-alkyl (Me, Et, i-Pr, and t-Bu) and 2-phenyl derivatives of 1,3-dioxa-5,6-benzocycloheptene (1) were studied by 13C dnmr. Analysis of slow exchange spectra at 100.6 MHz indicates that all derivatives except tert-butyl exist in an equilibrium of chair (major) and twist-boat (minor) conformations. Substituent effects on the position of the equilibrium are rationalized in terms of steric effects.

Direkte Lithiierung von BicycIo[3,2,1]octa-2.6-dien / Direct Lithiation of Bicyclo[3,2,1]octa-2,6-diene

1983 ◽  
Vol 38 (3) ◽  
pp. 407-408 ◽  
Author(s):  
Frank H. Köhler ◽  
Norbert Hertkorn
Keyword(s):  
Nmr Spectroscopy ◽  
Low Temperature ◽  
Mass Spectroscopy ◽  
Elemental Analysis ◽  
Derivatives Of

Abstract Bicyclo[3,2,1]octa-2,6-diene (1) has been lithiated directly with t-butyllithium/TMEDA at low temperature. After quenching with tri-methyltin chloride essentially two stannyl derivatives of 1 were obtained. The stannyl group did not bind to the allylic carbon of 1 as expected but to C-6 and C-7. This has been shown by means of elemental analysis, mass spectroscopy as well as 1H, 13C and 119 Sn NMR spectroscopy.

Part II. Conformational analysis of 4- and 5-substituted thiazolidine-2-thiones

1980 ◽  
Vol 58 (6) ◽  
pp. 604-616 ◽  
Author(s):  
F. Chanon ◽  
M. Rajzmann ◽  
M. Chanon ◽  
J. Metzger ◽  
G. Pouzard ◽  
...  
Keyword(s):  
Chemical Shifts ◽  
Alkyl Substituent ◽  
Chair Conformation ◽  
Equatorial Orientation ◽  
Anomeric Effect ◽  
H Nmr ◽  
Transannular Interaction ◽  
Conformational Properties ◽  
Out Of Plane ◽  
C Nmr

Variation of the conformational properties in a series of 4-R-thiazolidine-2-thiones (4-R = Me, Et, iPr, tBu, OH) and 5-R-thiazolidine-2-thiones (5-R = Me, Et, iPr, tBu) is deduced from 1H nmr (Karplus 3J, chemical shifts, 2J44′, 2J55′) 13C nmr data and CNDO-2 calculations. In the absence of any transannular interaction, vicinal constraints and van der Waals requirements of the substituents control the conformational equilibrium. The pseudo-axial arrangement is favoured when 4-R = Me, while the substituent presents no preferential orientation when 5-R = Me. As the size of the 5-alkyl and the 4-alkyl substituent increases, its pseudo-equatorial orientation and the predominance of the C4C5 out-of-plane half-chair conformation are favoured. This does not lead to conformational exclusivity even when 4-R or 5-R is tBu. When 4-R is hydroxy, there is a definite pseudo-axial conformation (anomeric effect) and the ring preference is of the C4 out-of-plane type.

scholarly journals Selektive Metallierung von BicycIo[3.2.1]octa-2,6-dien, II Distannylierte Derivate und stannylierte tricyclische Sekundärprodukte / Selective Metalation of Bicyclo[3.2.1]octa-2,6-diene, II Distannylated Derivatives and Stannylated Tricyclic Secondary Products

1988 ◽  
Vol 43 (11) ◽  
pp. 1405-1415 ◽  
Author(s):  
N. Hertkorn ◽  
F. H. Köhler
Keyword(s):  
Nmr Spectroscopy ◽  
Low Temperature ◽  
Nmr Spectra ◽  
Considerable Change ◽  
Coupling Constants ◽  
Secondary Products ◽  
Starting Compound ◽  
Derivatives Of ◽  
C Nmr ◽  
Dibromo Derivative

Abstract Distannylated bicyclo[3.2.1]octa-2,6-diene (1) with (CH3)3 Sn groups in positions exo-4 and 7 (7a), endo-4 and 7 (7b), exo-4 and 6 (7c), and probably exo-4 and endo-4 (7d) are obtained when 1 is treated first with an excess of n-BuLi/t-BuOK in alkane and then with (CH3)3 SnCl. Byproducts are monostannylated derivatives of 1 and l,4-bis(trimethylstannyl)but-2-ene (3). The formation of 7a/b/c is best understood when the two possible bicyclo[3.2.1]octa-2,6-dienyl dianions are generated as intermediates. 3,exo-4-Bis(trimethylstannyl)bicyclo[3.2.1]octa-2,6-diene (7e) is ob-tained from the corresponding dibromo derivative of 1 and (CH3)3SnLi with 3-bromo-exo-4-trimethylstannylbicyclo[3.2.1]octa-2,6-diene (9) as an intermediate. The bicyclic stannyl com-pounds are susceptible to a 1,5-homopentadienyl shift of a (CH3)3Sn group at relatively low temperature when the starting compound has the stannyl group in position 4 of 1 and when positions 6 or 7 are unsubstituted. Tricyclo[3.2.1.02.7]oct-3-enes with (CH3)3Sn groups in positions exo-6 (5a), endo-6 (5b), 3 and exo-6 (10a), and 3 and endo-6 (10b) are thus obtained. On further heating, 10b gives l-trimethylstannyl-3-vinylbenzene (11). All compounds have been studied systematically by NMR spectroscopy including δ(119Sn), δ(13C), δ(1H), 4/5J(119/117Sn-119Sn), nJ(119/117Sn-13C) , nJ(119/117Sn-1H), 1J(13C-1H ) , and nJ(1H-1H ). Among all nuclei, 119Sn gives the most simple spectra. From the 13C NMR spectra a series of useful increments of (CH3)3Sn groups emerges. The most interesting coupling constants are 5J(119/117Sn-119Sn), for which a considerable change with the dihedral angle is established, and nJ(119/117Sn-13C). For n = 3 and 4 the latter are especially useful because their angular dependence leads to unambiguous signal assignments.

Conformation of ring A of 19β,28-epoxy-18α-oleanan-3-one in solution and in the solid state. Crystal structure and carbon-deuterium stretching frequencies

1989 ◽  
Vol 54 (3) ◽  
pp. 737-750 ◽  
Author(s):  
Jiří Klinot ◽  
Jaroslav Podlaha ◽  
Jana Podlahová ◽  
Stanislav Hilgard ◽  
Eva Klinotová
Keyword(s):  
Crystal Structure ◽  
Solid Phase ◽  
Chair Conformation ◽  
Ether Bridge ◽  
Stretching Vibration ◽  
Boat Form ◽  
Derivatives Of ◽  
Phase Spectra ◽  
Twist Boat ◽  
Unusual Type

The crystal structure of allobetulone (I) has been determined. The compound is orthorhombic, P212121, a = 14.824(4), b = 25.701(7), c = 6.545(2) *A, Z = 4, R = 0.050 for 2 303 observed reflections. The rings B, C, D and E assume chair conformation, the chair of the ring E being considerably deformed by the ether bridge. The five-membered ether ring exists in an envelope form. The ring A assumes a boat form of an unusual type: one half has a typical classical boat geometry with coplanar atoms C(10), C(1), C(2) and C(3) whereas the other half resembles a twist boat. This conformation does not correspond to the published physical data found in solution. The conformation of ring A in crystal and in solution was further studied using IR spectra of 2α- and 2β-deuterio derivatives of allobetulone (II and III, respectively) in the carbon-deuterium stretching vibration region. The solid phase spectra are compatible with the boat form of ring A. Comparison of the solid phase spectra with solution spectra clearly indicates a chair-boat equilibrium in solution of the 3-oxo derivatives I-III. The carbon-deuterium stretching frequencies of other deuterium-labelled triterpenoid ketones (IV-VI) and alcohols (VII-X) are also discussed.

The synthesis and conformational properties of the diastereoisomeric βDGal(1→4)βDGlcNAc(1→6)6-C-CH3-D-Gal trisaccharides

1982 ◽  
Vol 60 (1) ◽  
pp. 81-86 ◽  
Author(s):  
Raymond U. Lemieux ◽  
Ting C. Wong ◽  
Henning Thøgersen
Keyword(s):  
Monoclonal Antibody ◽  
Nmr Spectroscopy ◽  
Molecular Modelling ◽  
Computer Assisted ◽  
Glycosidic Linkage ◽  
H Nmr ◽  
Conformational Preferences ◽  
Conformational Properties ◽  
Derivatives Of

The trisaccharide βDGal(1 → 4)βDGlcNAc(1 → 6)DGal was known to be bound strongly by the so-called anti-I Ma monoclonal antibody. In order to help assess the conformation about the 1 → 6 glycosidic linkage that is accepted by the antibody combining site, the conformationally well-defined βDGal(1 → 4)βDGlcNAc(1 → 6) derivatives of 7-deoxy-L-glycero-D-galacto-heptopyranose and 7-deoxy-D-glycero-D-galacto-heptopyranose were synthesized. The conformational preferences for these trisaccharides were established by 1H nmr spectroscopy and rationalized by computer-assisted molecular modelling.

Conformational study on ribonucleoside O-phosphonylmethyl derivatives by 1H NMR spectroscopy

1985 ◽  
Vol 50 (8) ◽  
pp. 1899-1905 ◽  
Author(s):  
Milena Masojídková ◽  
Jaroslav Zajíček ◽  
Miloš Buděšínský ◽  
Ivan Rosenberg ◽  
Antonín Holý
Keyword(s):  
Nmr Spectroscopy ◽  
1H Nmr ◽  
1H Nmr Spectroscopy ◽  
Conformational Study ◽  
H Nmr ◽  
Conformational Properties

Conformational properties of ribonucleoside 5'-O-phosphonylmethyl derivatives have been determined by 1H NMR spectroscopy and compared with those of natural nucleosides and 5'-nucleotides.

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