Use of ( E , E )-Dienoic Acids as Switchable ( E , E )- and ( Z , E )-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 ( E , E )-2,4-dienoic acids form electron-neutral and highest occupied molecular orbital-raised η 2 -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 ( E , E )- and ( Z , E )-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. An unprecedented formal reductive Mannich reaction between ( E , E )-dienoic acids and imines is also developed to furnish enantioenriched β-amino acid derivatives.