Pd-catalyzed decarboxylative asymmetric protonation (DAP) using (1R,2S)-(-)ephedrine as the proton source, previously developed for sterically hindered -aryl, lactone and dihydrocoumarin substrates, was applied to a range of -aryl -keto allyl ester substrates that were already successful in DAP with chiral P,N-ligands. An optimization study using a cyclopentanone-derived -aryl, -oxo-allyl ester with 2,4,6-trimethoxyphenyl as the aryl substituent afforded high levels of enantioselectivity (91% ee). This encouraged us to examine other -aryl, -keto-allyl ester substrates. The results from this substrate scope study with -aryl, cyclohexanone-, isoflavanone-, indanone-, and tetralone-derived substrates using (1R,2S)-(-)ephedrine as the protonating agent under Pd catalysis, compared favorably with enantioselectivities obtained in DAP reactions induced by Pd complexes of chiral ligands.
