What is the tautomeric behavior of the synthesized thiophenes and thiazoles, and how does it affect their structural properties?

The study reports the synthesis of various thiophenes and thiazoles from cyanothioacetamides and DMAD. The structural properties and tautomeric behavior of these compounds are important for understanding their potential applications and reactivity.

The tautomeric behavior of the synthesized compounds is as follows:
Thiazoles (4a-d): These compounds exist in a single form without observable tautomerism. Their 1H NMR spectra show doubling of signals, indicating the presence of isomers.
Thiophenes (5c,d): These compounds exhibit tautomerism, existing in equilibrium between keto and hydroxy forms. The 1H NMR spectra of these compounds show doubling of signals, which disappears at higher temperatures (80°C and 100°C), indicating tautomerization rather than the formation of regioisomers.
Thiophenes (8a-d): These compounds do not show doubling of signals in their 1H NMR spectra, indicating that they do not undergo tautomerism. They exist in a stable planar structure stabilized by intramolecular hydrogen bonds.