Ring Closure Reactions for the Synthesis of Cyclic Imines: An Analysis from the 12 Principles of Green Chemistry and Circular Chemistry

Compounds containing a C=N moiety, namely imines, have been widely used for industrial purposes due to their various biological activities. Cyclic imines are an essential class of nitrogen-based heterocycles and valuable scaffolds for designing and obtaining new biologically active compounds. However, the proposal and implementation of synthetic methods for this heterocyclic system are mainly conditioned by different structural and stereoelectronic considerations. Therefore, it can be complex and sometimes limited to a selected group of heterocyclic compounds. The following review paper is structured to search and collect different synthesis methods of cyclic imines and identify the main progress currently achieved. It addresses this topic using structural considerations, physical properties, and reactivity. The synthesis methods described below have implemented strategies based on cyclo-condensation reactions, radical cyclizations, electrocyclic closures, and carbon-carbon coupling by metal-organic catalysis. These methods have contributed significantly to organic chemistry knowledge. In addition, an analysis of such synthesis methods from applying the principles of green and circular chemistry is presented, evaluating the potential applications, limitations, perspectives, and impact of these methods on the environment.