An efficient method for the selective synthesis of δ-lactone from CO 2 and 1,3-butadiene was developed by using ultrasmall palladium nanoparticles as a catalyst for the first time. Palladium nanoparticles (1.90 � 0.39 nm) were generated in situ in the presence of Pd(acac) 2 , tetrabutylammonium acetate (TBAAc), and PPh 3 as the precatalyst, stabilizer, and reductant, respectively. Maximum yield (86 % with 96 % selectivity) with satisfactory conversion (89 %) and turnover number (1271) was achieved under mild conditions.

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The palladium‐catalyzed three‐component coupling of either (chloromethyl)arenes or (chloromethyl)heteroarenes with allyltrimethoxysilane and carbon dioxide (i.e., a carboxylative Hiyama coupling reaction) successfully produced α,β‐unsaturated esters in satisfactory to good yields. This reaction proceeded smoothly under mild conditions in the presence of palladium nanoparticles (NPs). A reaction mechanism, which includes the formation of an π‐allylpalladium chloride intermediate, has been proposed.