Metal-Free Decarboxylation of α,β-Unsaturated Carboxylic Acids for Carbon–Carbon and Carbon–Heteroatom Coupling Reactions

Metal-free decarboxylative coupling reactions represent an alternative paradigm for carbon–carbon or carbon–heteroatom bond formation that complement more traditional metal catalysis approaches. In this review, recent advances in metal-free decarboxylation reactions of α,β-unsaturated carboxylic acids are highlighted. Two major reaction classes are covered: 1) generation of C–C, C–N, C–S, C–X bonds using propiolic acids; 2) transformations of alkenyl acids for C–C, C–P, C–N, C–S, C–X bond-forming. Some cases involving electrochemistry and photochemistry represent a frontier area for carbon–carbon and carbon–heteroatom coupling processes. Additionally, the proposed mechanisms for both types of reactions are discussed. © 2020 SIOC, CAS, Shanghai & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim