Transition-Metal-Catalyzed α,β-Dehydrogenation of Carbonyl Compounds

α,β-Unsaturated compounds are one of the most important functional compounds. Due to their unique property and versatile utility, they usually occur as the key intermediates for the synthesis of pharmaceuticals and biological materials. Thus, their synthesis has attracted more attentions than before. The early approaches to α,β-unsaturated compounds are mainly about transition-metal-free methods, such as halogenation-dehydrohalogenation methods and strong oxidants methods (organosulfur, organoselenium, benzoquinone). Subsequently, palladium and the other transition-metals catalyzed dehydrogenation of carbonyl compounds appeared respectively. In this review, transition-metal-catalyzed α,β-dehydrogenation is discussed, which is categorized by functional groups.