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.

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.

Cis- and trans-2,4-dimethoxytetrahydropyran. Models for the study of the anomeric effect

1968 ◽  
Vol 46 (9) ◽  
pp. 1543-1548 ◽  
Author(s):  
F. Sweet ◽  
R. K. Brown
Keyword(s):  
Good Yield ◽  
Methoxy Group ◽  
Equilibrium Mixture ◽  
Anomeric Effect ◽  
Kcal Mole ◽  
Mild Acid Hydrolysis ◽  
Acid Catalyzed ◽  
Cis And Trans ◽  
Hydrolysis Of ◽  
Mild Acid

Acid-catalyzed methanolysis of 2-methoxy-5,6-dihydro-2H-pyran gave, in good yield, a 4.0:1.0 mixture of trans- and cis-2,4-dimethoxytetrahydropyran. Mild acid hydrolysis of 2-methoxy-5,6-dihydro-2H-pyran followed by acid-catalyzed reaction with methanol gave a cis-trans mixture of 4-hydroxy-2-methoxytetrahydropyran in very poor yield.From the equilibrium mixture of trans- and cis-2,4-dimethoxytetrahydropyran (4.0:1.0), the magnitude of the anomeric effect of the 2-methoxy group was calculated to be 1.4 kcal/mole.

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 conformational preference of methoxyl and acetoxyl groups in 3-oxycyclohexenes, 2-oxymethylenecyclohexanes, and 1-oxytetralins and the generalized anomeric effect

1987 ◽  
Vol 65 (8) ◽  
pp. 1761-1768 ◽  
Author(s):  
Adama Ouédraogo ◽  
Minh Tan Phan Viet ◽  
John K. Saunders ◽  
Jean Lessard
Keyword(s):  
Methoxyl Group ◽  
Equatorial Orientation ◽  
Anomeric Effect ◽  
Conformational Preference ◽  
Magnetic Resonance Data ◽  
Conformational Effect ◽  
Axial Conformer ◽  
Resonance Data ◽  
Cis And Trans ◽  
Derivatives Of

The 13C and 1H nuclear magnetic resonance data of 3-oxycyclohexenes, 2-oxymethylenecyclohexanes, and 1-oxytetralins show (i) that the pseudoaxial preference is larger for the acetoxyl group than for the methoxyl group in 3-oxycyclohexenes, (ii) that the methoxyl and the acetoxyl groups have the same pseudoaxial preference in 1-oxytetralins, and (iii) that in 2-oxymethylenecyclohexanes, the acetoxyl group prefers the equatorial orientation whereas the methoxyl group prefers to be axial. These results are interpreted in terms of the orbital picture (π–σ* stabilization of the axial conformer) of the generalized anomeric effect to which is opposed a conformational effect termed the "unsaturation effect" in 2-acetoxymethylenecyclo-hexane and probably also, but to a much smaller extent, in 1-acetoxytetralin. The results also show that cis and transtert-butyl analogues of 3-oxycyclohexenes do not represent the true limit conformers whereas cis and trans 4-tert-butyl derivatives of 2-oxymethylenecyclohexanes do not differ drastically from the limit conformers.

Orientation of the methoxyl group in cis- and trans-2-methoxy-4-methyl-1,3-dioxanes and related compounds as inferred by 1H and 13C nmr spectroscopy. The significance of the "exo-anomeric" effect

1982 ◽  
Vol 60 (9) ◽  
pp. 1067-1072 ◽  
Author(s):  
Vanga S. Rao
Keyword(s):  
Dynamic Equilibrium ◽  
Chemical Shifts ◽  
13C Nmr Spectroscopy ◽  
Methoxyl Group ◽  
Anomeric Effect ◽  
1H And 13C Nmr ◽  
Nuclear Overhauser ◽  
Cis And Trans ◽  
In Cis ◽  
Related Compounds

Carbon-13 chemical shifts and 13C—1H couplings are reported for some substituted 2-methoxy-1,3-dioxanes and related tetrahydropyran derivatives. These data, together with nuclear Overhauser enhancement experiments, provided evidence for a favored orientation of the methoxyl group. From an analysis of the 13C chemical shifts and the magnitude of vicinal 13C—1H coupling between —OCH3 and H-2, a possible dynamic-equilibrium orientation for the methoxyl group is proposed, and an evaluation of the significance of a "generalized exo-anomeric effect" is presented.

Stereoelectronic control in acetal formation

1980 ◽  
Vol 58 (23) ◽  
pp. 2531-2531 ◽  
Author(s):  
Normand Beaulieu ◽  
Robert A. Dickinson ◽  
Pierre Deslongchamps
Keyword(s):  
Experimental Evidence ◽  
Room Temperature ◽  
Equilibrium Mixture ◽  
Anomeric Effect ◽  
Equilibrium Study ◽  
Stereoelectronic Effects ◽  
Stereoelectronic Control ◽  
Acidic Conditions ◽  
Cis And Trans

The cyclization under acidic conditions of bicyclic and monocyclic hydroxypropyl methoxytetrahydropyrans 1 and 4 is reported. At room température, compound 1 gives only cis tricyclic acetal 2. At reflux, compound 2 equilibrates to yield a mixture of cis and trans tricyclic acetals 2 (45%) and 3 (55%). Compound 4 gives directly the equilibrium mixture of cis and trans bicyclic acetals 5 (55%) and 6 (45%) at room température. The specific formation of 2 from 1 constitutes strong experimental evidence that acetal formation is controlled by stereoelectronic effects. The anomeric effect can be estimated [Formula: see text] from the equilibrium study of 2 and 3. This value confirms the result previously obtained by Descotes (9).

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.

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