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 alpha,beta-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.