3,4-Dihydro-2(1H)-Pyridones as Building Blocks of Synthetic Relevance

3,4-Dihydro-2(1H)-pyridones (3,4-DHPo) and their derivatives are privileged structures, which has increased their relevance due to their biological activity in front of a broad range of targets, but especially for their importance as synthetic precursors of a variety of compounds with marked biological activity. Taking into account the large number of contributions published over the years regarding this kind of heterocycle, here, we presented a current view of 3,4-dihydro-2(1H)-pyridones (3,4-DHPo). The review includes general aspects such as those related to nomenclature, synthesis, and biological activity, but also highlights the importance of DHPos as building blocks of other relevant structures. Additional to the conventional multicomponent synthesis of the mentioned heterocycle, nonconventional procedures are revised, demonstrating the increasing efficiency and allowing reactions to be carried out in the absence of the solvent, becoming an important contribution to green chemistry. Biological activities of 3,4-DHPo, such as vasorelaxant, anti-HIV, antitumor, antibacterial, and antifungal, have demonstrated this heterocycle’s potential in medicinal chemistry.