Applications of 3-Substituted 2-Alkoxy- and 2-Alkylthiopropenals in Organic Synthesis

α-Functionally substituted α,β-unsaturated aldehydes belong to the highly reactive class of compounds. They are used as versatile building blocks in organic synthesis. Due to the presence of several reactive sites in their structure, α,β-unsaturated aldehydes are widely employed as precursors of various acyclic and heterocyclic compounds, as well as complex natural products. At the same time, the acrylic systems with heteroatomic substituents (OAlk, SAlk) in the α-position are poorly studied. Therefore, it is impossible to establish the distribution of electron density reliably and evaluate the real reactivity of each new representative of this class of compounds. This minireview summarizes the works demonstrating the broad applicability of 3-substituted 2-alkoxy and 2- alkylthiopropenals in organic synthesis.