Deciphering the Origin of Stereoinduction in Cooperative Asymmetric Catalysis Involving Pd(II) and a Chiral Brønsted Acid.
The density functional (M06) computations on a cooperative multicatalytic reaction involving palladium acetate and a chiral Brønsted acid in the conversion of an indenyl cyclobutanol to spirocyclic indene bearing a quaternary carbon ring junction are reported. A chiral Pd-bis-phosphate is identified as the active catalyst in the enantioselective ring expansion as compared to alternative possibilities wherein the chiral phosphate/phosphoric acid is in the outer sphere of palladium. The enantiocontrolling transition state exhibited more effective C-H···π interactions, lower distortion of the catalyst, and an orthogonal orientation of the bulky phosphate ligands.