Heterocyclic Conformational Analysis

Banfi L, Basso A, Guanti G, Lecinska P, Riva R, Rocca V (2007) Multicomponent synthesis of novel 2- and 3-substituted dihydrobenzo[l, 4]oxazepinones and tetrahydrobenzo[ 1, 4] diazepin-5-ones and their conformational analysis. Heterocycles 73 699-728... 

Application of NMR spectroscopy to heterocyclic chemistry has developed very rapidly during the past 15 years, and the technique is now used almost as routinely as H NMR spectroscopy. There are four main areas of application of interest to the heterocyclic chemist (i) elucidation of structure, where the method can be particularly valuable for complex natural products such as alkaloids and carbohydrate antibiotics (ii) stereochemical studies, especially conformational analysis of saturated heterocyclic systems (iii) the correlation of various theoretical aspects of structure and electronic distribution with chemical shifts, coupling constants and other NMR derived parameters and (iv) the unravelling of biosynthetic pathways to natural products, where, in contrast to related studies with " C-labelled precursors, stepwise degradation of the secondary metabolite is usually unnecessary. 

Conformation analysis of saturated six-member 0-heterocycles 98AHC (69)217. 

See G.F. Riddell, "The Conformational Analysis of Heterocyclic Compounds", pags. 139-140, Academic Press, London, 1980. 

Conformational Analysis of Saturated Six-Membered Oxygen-Containing Heterocyclic Rings... 

The best method used in the conformational analysis of saturated six-membered heterocyclic rings in the solid state is single-crystal X-ray structural analysis. The conformation in solution is not always identical. For solutions, H NMR spectroscopic analysis has been employed widely in the field of conformational analysis. The following methods deserve special mention. 

Conformational analysis of proanthocyanidins is, in principle, concerned with the conformation of the pyran heterocycle and with the phenomenon of conformational isomerism due to... 

B-80MI20401 F. G. Ridell The Conformational Analysis of Heterocyclic Compounds ,... 

Measurements of dipole moments, Kerr constants, and dielectric absorption have been employed (81RCR336) widely to obtain information on the conformational equilibrium in acyl heterocycles. Details on conformer structures and populations depend on the choice of additive scheme, group moments, or polarizability tensor in the case of Kerr constants. Several early conclusions, especially for furan- and thiophene-2-carboxaldehyde, appeared contradictory, owing to the choice of these quantities. A more precise definition of polarizability tensors for several heterocycles and a choice of group moments and additive schemes tested on a large amount of available experimental results and supported by accurate theoretical calculations have led to more confidence in the use of experimental dipole moments and Kerr constants in conformational analysis. A limitation of the method is that the... 

As mentioned in connection with the benzoyl derivatives of five-membered heterocycles, conformational analysis of benzoyl derivatives of pyridine suffers from the indetermination connected with the necessity of simultaneously assigning N,0-cis/trans populations and conformer structures from experimental results. The all-planar conformations should be excluded... 

Theoretical conformational analysis provides a basis for understanding the unique features of double-stranded DNA In terms of its chemical architecture. The well-known stiffness of the chain as a whole derives from the sequence of heterocyclic bases, while the local mobility of the constituent nucleotides reflects the structural complexity of the sugar-phosphate backbone. 

Emphasis is placed on simply substituted free bases. The problems of conformational equilibria in /V-alkylpiperidinium salts and N-quaternization reactions and the relationships of these to conformational equilibria in the free bases are not covered, since this area is a large one requiring separate treatment. In other relevant previous reviews, the topics include heterocyclic conformational analysis,3-7 interactions in azacyclic systems,8 the conformational analysis of piperidine,9 hexahydropyrimidines,10,11 hexahydropyri-dazines,12 quinolizidines,13 the conformational analysis of bi- and polycyclic... 

Photoelectron spectroscopy145 has been particularly useful in the conformational analysis of heterocyclic molecules possessing vicinal electron lone pairs, especially in the hexahydropyridazine system.12,145a In such a system the two lone-pair orbitals on nitrogen do not ionize at the same potential because of interactions with each other and with other orbitals. Lone-pair-lone-pair interactions are expected to dominate and are dependent upon the... 

Conformational Analysis , F. G. Riddell, in Heterocyclic Chemistry , ed. H. Suschitzky and O. Meth-Cohn, Royal Society of Chemistry, London, 1980, vol. 1, pp. 469-488. 

Conformational Analysis of Sulphur-Containing Six-Membered Heterocycles N. S. Zefirov and I. V. Kazimirchik, Russ. Chem. Rev. (Engl. Transl.), 1974, 43, 107-114. 

Conformational Analysis in Heterocyclic Systems Recent Results and Applications E. L. Eliel, Angew. Chem., Int. Ed. Engl., 1972,11, 739-750. 

Conformational Analysis in Multisulfur Heterocycles C. H. Bushweller, Mech. React. Sulfur Compd., 1970, 5, 75-85. 

Conformational Analysis in Saturated Heterocyclic Compounds E. L. Eliel, Acc. Chem. Res., 1970, 3, 1-8. 

E. L. Eliel, Insights gamed from conformational analysis in heterocyclic systems, Pun Appl. Chem. 25 509 (1971). 

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