Enantioselecitve elimination of Pd-H from η ³-allylpalladium- tol BINAP complexes. Evidence of Syn elimination pathway

The palladium-catalyzed elimination of the bicyclic cis-acetate lb using Pd catalyst and (R)-p-Tol BINAP gave the (S)-diene 2 with 58% ee. Bicyclic η ³-allylpalladium complex 3a with (R)-p-Tol BINAP, considered as an intermediate in the catalytic reaction from lb, was prepared. Enantioselectivity in decomposition of 3a is dependent on the reaction conditions. The thermal decomposition of 3a without base gave the (S)-2 with 70% ee. However, the decomposition of 3a in the presence of excess base gave (R)-2 with 58% ee. Syn elimination from 3a was found to proceed preferentially from the decomposition results of the deuterium-labeled complexes.