Formyl heterocycles, conformation

Studies of the conformations of 2-formyl and 2-acetyl derivatives of the five-membered heterocycles have attracted great interest in recent years, but some of the results have been contradictory. At low temperatures the interconversion of the two conformers, trans-SS and cis-86, is slow, and can be studied by NMR. Thus, the 1H-NMR spectra of some selenophene deriva-... 

Thus, aside from furan-2-carboxaldehyde, where the equilibrium between conformers is rather sensitive to external effects, the 2-formyl derivatives of five-membered heterocycles are rather rigid from a conformational point of view. 

Detailed and accurate studies on the influence of solvent polarity on the conformational equilibrium of 3-formyl derivatives of five-membered heterocycles are not yet available and from experimental results it is difficult to assess... 

Several diformyl derivatives of five-mem bered heterocycles were studied with regard to their conformational properties. Although one formyl group may be considered to behave as a substituent with respect to the other perturbing its conformational equilibrium, in 2,5- and in 2,4-derivatives the groups behave quite independently. In principle, for these compounds four conformations are possible, represented by 15 for 2,5-diformyl derivatives. In... 

The conformation of the formyl group when bonded to the six-membered ring of a number of benzocondensed five-membered heterocycles is also known (83JCS(P2)911 83TL2367 84JCS(P2)1479). The orientation of the... 

More accurate investigations on acyl derivatives of five-membered aromatic heterocycles need to be carried out, to replace earlier results and to provide homogeneous sets of energy differences between conformers and energy barriers, if possible, also in different physical conditions. For the 3-formyl and, in general, 3-acyl derivatives, the influence of solvent polarity must be more carefully examined. 

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