Palladium-Catalyzed Carboxylative Coupling Of Benzyl Chlorides, CO₂and Allyltributylstannane

Carbon dioxide (CO2) is an ideal carbon source owing to its abundance, low cost, nontoxicity, and good potential as a renewable source. However, it is quite difficult to activate such a thermodynamically and kinetically stable material. Therefore, catalysts play an important role in development of useful transformations utilizing this attractive and environmentally friendly raw material. Numerous methods have been developed for CO2fixation over the past decades. Among these methods, the transition-metal-catalyzed activation and conversion of CO2into valuable chemicals that involve new carbon-carbon bond formation have recently emerged as extremely powerful tools because of their high chemoselectivity, good functional group tolerance and mild reaction conditions.In this paper, palladium-catalyzed carboxylative coupling of benzyl chlorides, CO2and allyltributylstannane was investigated. The main contents were summarized below:1. The carboxylative coupling of benzyl chloride, CO2and allyltributylstannane was selected as the model reaction. The effects of various factors on the reaction were investigated, and the optimum reaction conditions were established:Pd(acac)2(5mol%) as precatalyst, TBAB (1.4equiv) as additive, CO2(2.0MPa), THF (5mL) as solvent, maintaining reaction at70℃for24h. Under the above optimum reaction conditions, the carboxylative coupling of various benzyl chlorides, CO2and allyltributylstannane was examined, and the yields were between64%and86%.2. It was found that when benzyl chlorides bearing electron-donating or weak electron-withdrawing groups was used as a substrate, a good yield of product could be obtained. However, when benzyl chlorides bearing strong electron-withdrawing groups was used as a substrate, the yield of the product was decreased a bit. Besides, the reaction of chloromethyl naphthalene could also provide a good yield of the target product.