The Chemistry of Aldehydes and Ketones in the Synthesis of Heterocycles - Historical Reactions with a New and Green Perspective

: The reactivity of aldehydes and ketones carries great potential for multicomponent heterocyclizations. These reactions are convergent and highly versatile in the development of synthetic methodologies for compound families, displaying variations in substituents in their structures. Therefore, they have been regarded as an important tool in the field of Green Chemistry. Furthermore, they prove to be very useful in studies of biological activity, where small structural modifications can result in significant differences. Many heterocyclizations date back to the mid-19th and early 20th centuries. In this review, we aim to demonstrate, through some of these reactions, their continuously growing potential and improvements concerning synthetic development. Additionally, we present the original studies as reported, enabling us to appreciate the evolution of chemical representations over the years until reaching the standardization we have today.