The Intermolecular Asymmetric Heck Reaction: Mechanistic and Computational Studies

Reactive intermediates in the asymmetric Heck reaction between aryl electrophiles and 2,3‐dihydrofuran have been identified by NMR and mass spectrometry, with BINAP or the achiral diphosphanes dppp and dppf as ligands. The major cationic species observed is an alkylpalladium produced by addition of PdAr to the alkene followed by two further PdH‐mediated isomerisation steps. This last species has been characterised at −60° by ¹H‐, ¹³C‐, and ³¹P‐NMR, including HMQC techniques. The regiochemistry of PdAr and PdH addition to the reactant are opposite as defined by the reaction with (2‐²H₁)‐2,3‐dihydrofuran. DFT Calculations on the reaction pathway between CH₂(PH₂)]PdPh⁺ and 2,3‐dihydrofuran reveal several structurally interesting intermediates involving agostic β‐H‐atom, ipso‐Ph or reactant O‐atom bonded to the Pd‐atom, and elucidate the isomerisation pathway.