Redox Reaction of the Pd0 Complex Bearing the Trost Ligand with meso-Cycloalkene-1,4-biscarbonates Leading to a Diamidato PdII Complex and 1,3-Cycloalkadienes: Enantioselective Desymmetrization Versus Catalyst Deactivation

The Pd0 complex 1 that bears the Trost ligand 2 undergoes a facile redox reaction with 1,4‐biscarbonates 5 b–d and rac‐22 under formation of the diamidato–PdII complex 7 and the corresponding 1,3‐cycloalkadienes 8 b–d. The redox deactivation of complex 1 was the dominating pathway in the reaction of 5 b–d with HCO3− at room temperature. However, at 0 °C the six‐membered biscarbonate 5 b, catalytic amounts of complex 1, and HCO3− mainly reacted in an allylic alkylation, which led to a highly selective desymmetrization of the substrate and gave alcohol 6 b with ≥99 % ee in 66 % yield. An increase of the catalyst loading in the reaction of 5 b with 1 and HCO3− afforded the bicyclic carbonate 12 b (96 % ee, 92 %). Formation of carbonate 12 b involves two consecutive inter‐ and intramolecular substitution reactions of the π‐allyl–PdII complexes 16 b and 18 b, respectively, with O‐nucleophiles and presumably proceeds through the hydrogen carbonate 17 b as key intermediate. The intermediate formation of 17 b is also indicated by the conversion of alcohol rac‐6 b to carbonate 12 b upon treatment with HCO3− and 1. The Pd0‐catalyzed desymmetrization of 5 b with formation of 12 b and its hydrolysis allow an efficient enantioselective synthesis of diol 13 b. The reaction of the seven‐membered biscarbonate 5 c with ent‐1 and HCO3− afforded carbonate ent‐12 c (99 % ee, 39 %). The Pd0 complex 1 is stable in solution and suffers no intramolecular redox reaction with formation of complex 7 and dihydrogen as recently claimed for the similar Pd0 complex 9. Instead, complex 1 is rapidly oxidized by dioxygen to give the stable PdII complex 7. Thus, formation of the PdII complex 10 from 9 was most likely due to an oxidation by dioxygen. Oxidative workup (air) of the reaction mixture stemming from the desymmetrization of 5 c catalyzed by 1 gave the PdII complex 7 in high yield besides carbonate 12 c. Desymmetrization versus deactivation: The Pd0/Trost ligand complex and allylic 1,4‐biscarbonates undergo a facile redox reaction with the formation of a diamidato PdII complex and 1,3‐dienes. The catalytic desymmetrization of the meso‐biscarbonate with the Pd0/Trost ligand complex and HCO3− delivers, with high enantioselectivity, the corresponding alcohol and/or bicyclic carbonate (see scheme). The Pd0/Trost ligand complex is stable in the absence of dioxygen.