钯催化二氧化碳为羰基源的羧基化反应

Recent advances in the Pd-catalyzed carboxylation reactions using carbon dioxide as carbonyl source

二氧化碳是地球上蕴藏最为丰富的C1资源,其资源化利用一直是有机化学研究前沿及热点领域之一.其中,过渡金属催化以二氧化碳为羰基源的羧基化反应可以有效构建很多具有重要应用价值的羧酸及其衍生物,是实现二氧化碳资源化利用的理想途径之一,日益受到科学家的关注.钯是有机合成中用途最广的重要过渡金属之一,钯催化剂具有高反应活性、高选择性等特点,在二氧化碳羧基化反应中发挥重要的作用.本文主要聚焦于钯催化二氧化碳参与的形成碳-碳键的羧基化反应,着重从反应机理出发,分别阐述了各类烯丙基、芳基和烯烃等试剂与二氧化碳羧基化反应研究进展,并对这些反应进行总结以及对未来的发展方向进行展望.

Carbon dioxide is the most abundant C1 resource on the Earth, and its resource utilization has been one of the hot spots and the frontiers research of organic chemistry. Among them, the transition metal catalyzed carboxylation reactions with carbon dioxide as carbonyl source provided high atom-economical strategies for the construction of an array of carboxylic acids and their derivatives, which were regarded as one of the most effective approaches for the utilization of carbon dioxide. In recent years, various transition metals such as nickel, copper, palladium, gold, rhodium, cobalt and iron have been widely applied in the carboxylation of carbon dioxide. Based on our research interest in palladium-catalyzed coupling reactions, in this paper, we reviewed the recent research progress of the Pd-catalyzed carboxylation with carbon dioxide as carbonyl source. There are several types of the Pd-catalyzed carboxylation reactions, including:(1) The Pd-catalyzed carboxylation reactions of the carbon dioxide with allylic, butadiene, allenes compounds, respectively, which underwent the nucleophilic addition of σ-allyl palladium species to carbon dioxide;(2) the Pd-catalyzed carboxylation reactions of the carbon dioxide with aryl bromides, aryl triflates, respectively, in which the aryl palladium species were generated via the oxidation addition of aryl reagents with Pd(0), followed by the insertion of carbon dioxide;(3) the Pd-catalyzed carboxylation reactions of the carbon dioxide with unactivated aryl sp2 C-H bonds, which proceeded the concertedmetalation-deprotonation process to produce the palladacycle intermediate, followed by the insertion of two molecules of carbon dioxide into the hetero-palladium bond of palladacycle intermediate;(4) the Pd-catalyzed carboxylation reaction of ethylene and carbon dioxide via the oxidation cycloaddition process to generate five-membered palladalactones intermediate;(5) the Pd-catalyzed carboxylation reactions of carbon dioxide with organozinc reagents, which underwent the transmetalation of Pd-CO2 complex with organozinc reagents to form organopalladium species, followed by the reductive elimination. Although some progress as mentioned above has been made in the Pd-catalyzed carboxylation involving carbon dioxide, there are still some challenges in the catalytic carboxylation reactions, such as the limited substrates scope, harsh reaction conditions, the asymmetric carboxylation reactions, the industrial production of carboxylic compounds, and so on. Therefore, the development of highly effective catalytic systems is the key to address these issues.Palladium catalysts exhibit great potential in the carboxylation of carbon dioxide due to the advantages of versatility, high selectivity and strong functional group tolerance of palladium catalyzed reactions. This paper is intended to provide some advices for the development of palladium-catalyzed carboxylation reactions involving carbon dioxide for the formation of carbon-carbon bonds.