Anomeric effects of sulfones

2002 ◽  
Vol 80 (8) ◽  
pp. 894-899 ◽  
Author(s):  
Guangwu Chen ◽  
Richard W Franck ◽  
Guangli Yang ◽  
Michael Blumenstein
Keyword(s):  
Anomeric Effect ◽  
Methyl Group ◽  
Sulfone Group ◽  
A Value ◽  
Anomeric Effects ◽  
Equatorial Conformer

The anomeric effect of the sulfone group in tetrahydropyrans has been determined. The value is >2 kcal mol–1, which is larger than the A-value of a methyl group but less than the A-value of the sulfone in a tetrahydropyran. Hence, in an unsubstituted tetrahydropyranyl sulfone, the equatorial conformer predominates, whereas in a properly substituted methyltetrahydropyranyl sulfone, an axial sulfone is preferred over an axial methyl group.Key words: sulfone, tetrahydropyran, anomeric effect.

Some reactions of 2,4-dimethoxytetrahydropyrans

1969 ◽  
Vol 47 (17) ◽  
pp. 3099-3106 ◽  
Author(s):  
M. J. Baldwin ◽  
R. K. Brown
Keyword(s):  
Room Temperature ◽  
Equilibrium Mixture ◽  
Anomeric Effect ◽  
Temperature Reaction ◽  
Trans Isomers ◽  
Kcal Mole ◽  
A Value ◽  
Cis And Trans Isomers ◽  
Acid Catalyzed ◽  
Cis And Trans

Acid-catalyzed elimination of methanol from 2,4-dimethoxytetrahydropyran (1) produces 2-methoxy-5,6-dihydro-2H-pyran (3) rather than the expected olefin 4-methoxy-3,4-dihydro-2H-pyran (2).The reaction of 1,3-dibromo-5,5-dimethylhydantoin with 3 in ether – methanol gives a 2:1 mixture of the isomers 3β-bromo-2α,4α-dimethoxytetrahydropyran (5a) and 3α-bromo-2α,4β-dimethoxytetrahydropyran (5b) respectively. A rationale is given to explain the preponderance of 5a over 5b and the highly selective attack of the bromine of the hydantoin and the methanol on C-3 and C-4 respectively of the double bond of 3. Reduction of 5ab with zinc in ethanol provides only compound 3.The room temperature reaction of 1 in a mixture of water and 1,2-dimethoxyethane containing Amberlite IR-120, produces 2-hydroxy-4-methoxytetrahydropyran (6) as an equilibrium mixture of cis and trans isomers in the ratio 1:1. This gave a value of 0.9 kcal/mole for the anomeric effect in 6. Pyrolysis of the derivative, 2-acetoxy-4-methoxytetrahydropyran failed to produce the olefin 2 and resulted only in extensive decomposition.

N-[2-(Pyridin-2-yl)ethyl]-derivatives of methane-, benzene- and toluenesulfonamide: prospective ligands for metal coordination

2013 ◽  
Vol 69 (11) ◽  
pp. 1397-1401 ◽  
Author(s):  
Danielle L. Jacobs ◽  
Benny C. Chan ◽  
Abby R. O'Connor
Keyword(s):  
Hydrogen Bonding ◽  
Dihedral Angles ◽  
Compound I ◽  
Torsion Angles ◽  
Methyl Group ◽  
A Value ◽  
Π Stacking ◽  
Linear Chains ◽  
Centroid Distance ◽  
Derivatives Of

The molecular and supramolecular structures are reported ofN-[2-(pyridin-2-yl)ethyl]methanesulfonamide, C8H12N2O2S, (I),N-[2-(pyridin-2-yl)ethyl]benzenesulfonamide, C13H14N2O2S, (II), andN-[2-(pyridin-2-yl)ethyl]toluenesulfonamide, C14H16N2O2S, (III). Although (II) and (III) are almost structurally identical, the N(amide)—C(ethyl)—C(ethyl)—C(pyridinyl) torsion angles for (I) and (II) are more closely comparable, with magnitudes of 175.37 (15)° for (I) and 169.04 (19)° for (II). This angle decreases dramatically with an additional methyl group in theparaposition of the sulfonamide substituent, resulting in a value of 62.9 (2)° for (III). In each of the three compounds there is an N—H...N hydrogen bond between the sulfonamide of one molecule and the pyridine N atom of a neighbor. Compound (I) forms hydrogen-bonded dimers, (II) uses its hydrogen bonding to connect supramolecular layers, and the hydrogen bonding of (III) connects linear chains to form layers. For arene-substituted (II) and (III), the different conformations afforded by the variable dihedral angles promote intermolecular π–π stacking in the benzene-substituted structure (II), but distorted intramolecular T-shaped π-stacking in the toluene-substituted structure (III), with a centroid-to-centroid distance of 4.9296 (10) Å.

scholarly journals Heteroatom Substitution at Amide Nitrogen—Resonance Reduction and HERON Reactions of Anomeric Amides

Molecules ◽  
2018 ◽  
Vol 23 (11) ◽  
pp. 2834 ◽  
Author(s):  
Stephen Glover ◽  
Adam Rosser
Keyword(s):  
Amide Bond ◽  
Anomeric Effect ◽  
Amide Nitrogen ◽  
Carbonyl Carbon ◽  
Heteroatom Substitution ◽  
Electronegative Atom ◽  
Anomeric Effects ◽  
Acyl Derivatives

This review describes how resonance in amides is greatly affected upon substitution at nitrogen by two electronegative atoms. Nitrogen becomes strongly pyramidal and resonance stabilisation, evaluated computationally, can be reduced to as little as 50% that of N,N-dimethylacetamide. However, this occurs without significant twisting about the amide bond, which is borne out both experimentally and theoretically. In certain configurations, reduced resonance and pronounced anomeric effects between heteroatom substituents are instrumental in driving the HERON (Heteroatom Rearrangement On Nitrogen) reaction, in which the more electronegative atom migrates from nitrogen to the carbonyl carbon in concert with heterolysis of the amide bond, to generate acyl derivatives and heteroatom-substituted nitrenes. In other cases the anomeric effect facilitates SN1 and SN2 reactivity at the amide nitrogen.

Configuration and conformation of alkoxyalkyl and hydroxyalkyl trifluoromethyl nitroxides. Anomeric effects and nitroxide conformations

1981 ◽  
Vol 59 (12) ◽  
pp. 1745-1752 ◽  
Author(s):  
C. Chatgilialoglu ◽  
K. U. Ingold
Keyword(s):  
Anomeric Effect ◽  
Conformational Preference ◽  
Nodal Plane ◽  
Spectral Parameters ◽  
Small Magnitude ◽  
Or Groups ◽  
Steric Factors ◽  
Hyperfine Splittings ◽  
Anomeric Effects ◽  
Configuration And Conformation

The epr spectral parameters for some [Formula: see text] radicals have been measured over a range of temperatures. These radicals are probably non-planar at nitrogen. Their OR groups are in the eclipsed position with respect to the N 2pz orbital, a conformational preference which is attributed to a combination of steric factors and the anomeric effect. For [Formula: see text] the H hyperfine splittings (hfs) are of unusually small magnitude. It is pointed out that all other known [Formula: see text] also have anomalously low H hfs. It is suggested that this is due to the anomeric effect which not only promotes the eclipsed conformation but also causes the OR group to bend towards the semioccupied orbital, thereby moving H and R2 towards the nodal plane of this orbital.

The “A” value for the methyl group in 2-methylpiperidines

1974 ◽  
Vol 15 (47) ◽  
pp. 4169-4172 ◽  
Author(s):  
Robert R. Fraser ◽  
T. Bruce Grindley
Keyword(s):  
Methyl Group ◽  
A Value

The anomeric and reverse anomeric effect. A simple energy decomposition model for acetals and protonated acetals

1992 ◽  
Vol 70 (5) ◽  
pp. 1562-1572 ◽  
Author(s):  
F. Grein ◽  
P. Deslongchamps
Keyword(s):  
Lone Pair ◽  
Electronic Energy ◽  
Anomeric Effect ◽  
Energy Term ◽  
Energy Decomposition ◽  
Additional Energy ◽  
Relative Stabilities ◽  
A Value ◽  
Stabilization Energies ◽  
A Charge

Geometry optimizations at the 6-31G** level were performed on various conformers of XHmCH2YHn and XHmCH2YHn+I+ (protonated), with X, Y = N, O. The resulting anomeric stabilization energies were decomposed into steric, electrostatic (lone pair – lone pair, lone pair – hydrogen), and electronic contributions. Using approximate values for steric and electrostatic terms, the electronic energy was determined to be about −2 kcal/mol for the anomeric effect to arise from O, and −2.5 kcal/mol if it arises from N. For protonated systems, an additional energy term for the reverse anomeric effect had to be added, having a value of −4 kcal/mol for O in OH-CH2-NH3+ and −5 kcal/mol for N in NH2C-H2-NH3+. The anomeric effect due to N drives NH2-CH2-OH2+ to a charge-dipole complex of the type NH2=CH2+… OH2. The energy parameters obtained have been applied to predict relative stabilities of various conformers of methanetriol, aminomethanediol, and protonated methanetriol, with good success.

Ab initio modelling of the anomeric and exo anomeric effects in 2-methoxytetrahydropyran and 2-methoxythiane corrected for intramolecular BSSE

2015 ◽  
Vol 17 (28) ◽  
pp. 18501-18513 ◽  
Author(s):  
Vladimir Sladek ◽  
Filip Holka ◽  
Igor Tvaroška
Keyword(s):  
Ab Initio ◽  
Anomeric Effect ◽  
Oxygen Substitution ◽  
Anomeric Effects

Oxygen substitution in 2-methoxytetrahydropyran by sulphur in 2-methoxythiane approximately doubles the anomeric effect, which slows down enzymatic processing of 2-methoxythiane.

Halogenated Terpenoids. XXIX The 1-Bromo 1-Bromomethyl Cyclohexyl System

1997 ◽  
Vol 50 (7) ◽  
pp. 689 ◽  
Author(s):  
Douglas J. Brecknell ◽  
Raymond M. Carman ◽  
Ross A. Edwards ◽  
Karl A. Hansford ◽  
Tomislav Karoli ◽  
...  
Keyword(s):  
Free Energy ◽  
Bromine Atom ◽  
Methyl Group ◽  
X Ray ◽  
X Ray Crystallography ◽  
Bromo Derivative ◽  
A Value ◽  
Derivative Free ◽  
Methylene Groups

Bromination of methylene groups exocyclic to cyclohexyl systems normally affords two isomeric products; the axial 1-bromo equatorial 1-bromomethyl compound and the axial 1-bromomethyl equatorial 1-bromo derivative. Free energy differences between these two isomers, and the conformations adopted by the axial 1-bromomethyl group, have been explored by n.m.r. spectroscopy, by X-ray crystallography and by MM3 calculations. Evidence is presented to show that the ax-bromomethyl group exists primarily as those rotamers which site the bromine atom synclinal to the vicinal bromine. The A value for a bromomethyl group in this system is then similar to that of an unsubstituted methyl group.

Synthesis and equilibration of conformationally rigid cis and trans tricyclic mono and dithioacetals. An evaluation of stereoelectronic (anomeric) effects in thioacetals

1985 ◽  
Vol 63 (10) ◽  
pp. 2757-2762 ◽  
Author(s):  
Pierre Deslongchamps ◽  
Daniel Guay
Keyword(s):  
Anomeric Effect ◽  
Cis And Trans ◽  
Anomeric Effects

The synthesis of cis and trans tricyclic monothioacetals 5–8 and dithioacetals 9 and 10 is reported (Schemes 1 and 2). The cis isomers 5, 7, and 9 are the kinetic products of cyclization, a result which is explained on the basis of stereoelectronic principles. Equilibration studies (Table 1) led to an evaluation of the anomeric effect for sulfur; it was found to be of the same order as that for oxygen.

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