Synthesis of 1-(Difluoromethyl)alk-1-enes via Palladium-Catalyzed SN2′-Type Substitution Reaction of Difluoromethylated Allylic Phosphates with 1,3-Dicarbonyl Compounds and Imides
2020
Yamamoto, Yoshihiko | Sakai, Motoji | Ishida, Yuki | Yasui, Takeshi
Herein, we report the synthesis of 1-(difluoromethyl)alkenes via a palladium-catalyzed reaction of difluoromethyl-substituted allylic phosphates with 1,3-dicarbonyl compounds using PdCl₂(PPh₃)₂ as a precatalyst. 1,3-Dicarbonyl compounds attacked the γ-carbon with respect to the difluoromethyl group to afford their corresponding SN2′-type substitution products irrespective of the substitution pattern in the allylic phosphates. This regioselectivity has been ascribed to the electronic environment of the unsymmetrical π-allylpalladium intermediate using density functional theory (DFT) calculations. The reaction of difluoromethyl-substituted allylic phosphates with imides was also carried out using a different catalyst system composed of [PdCl(η³-allyl)]₂ and di(diphenylphosphino)butane (dppb).
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