Use of (,)-Dienoic Acids as Switchable (,)- and (,)-Dienyl Anion Surrogates via Ligand-Controlled Palladium Catalysis.

Carboxylic acids are not readily applied as carbon-based nucleophiles due to their intrinsic acidic group. Here, we demonstrate that free (,)-2,4-dienoic acids form electron-neutral and highest occupied molecular orbital-raised η-complexes with Pd(0) and undergo Friedel-Crafts-type additions to imines with exclusive α-regioselectivity, giving formal dienylated products after decarboxylation. Unusual and switchable (,)- and (,)-selectivity, along with excellent enantioselectivity, is achieved via ligand-controlled outer-sphere or inner-sphere reaction modes, respectively, which are well supported by comprehensive density functional theory calculation studies.