Tautomerism, Z/E isomerization, and H-bonding in the amino and N-hetaryl derivatives of carbonyl compounds

In the present review, two types of compounds capable of tautomerization with proton transfer between N and O atoms, isomerization by rotation about the CC or CN bonds, and hydrogen bonding in specific isomers are analyzed, focusing on the last two decades. The first type is enaminones attracting a growing interest as synthetic precursors of heterocycles, or, structurally, as push-pull ethylenes. This reduces the barrier to rotation around the double bond, and increases the barrier to rotation around the adjacent single bond. Another type of compounds also capable of tautomerism, conformational and rotational equilibrium, and the hydrogen bonding, is keto- or diketoenols with aromatic N-heterocycles at the CC bond which have been investigated mainly by our research groups. Overall, the review summarizes recent advances in studying E/Z isomerization, tautomerism, H-bonding in enaminones and ketoenols, and relationship between these phenomena.