An improved class of phosphite-oxazoline ligands for Pd-catalyzed allylic substitution reactions

Identifier:  imarina:5874117

Handle: https://hdl.handle.net/20.500.11797/imarina5874117

Authors:  Biosca, Maria; Salto, Joan; Magre, Marc; Norrby, Per-Ola; Pamies, Oscar; Dieguez, Montserrat

Abstract:
© 2019 American Chemical Society. A method for generation of Pd/phosphite-oxazoline catalysts containing an alkyl backbone chain has been successfully applied to Pd-catalyzed allylic substitution reactions. By carefully selecting the substituents at both the alkyl backbone chain and the oxazoline of the ligand, as well as the configuration of the biaryl phosphite group, high activities (TOF > 8000 mol substrate × (mol Pd × h)−1) and excellent enantioselectivities (ee's up to 99%) have been achieved for many hindered and unhindered substrates with a wide range of C-, O-, and N-nucleophiles (73 substitution products in total). Moreover, DFT and NMR studies of the key Pd-allyl complexes allowed us to better understand the origin of the excellent enantioselectivities observed experimentally. The useful application of the Pd/phosphite-oxazoline catalysts was demonstrated by the syntheses of many chiral carbobicycles, with multiples stereocenters, by simple sequential reactions involving Pd-allylic substitution and either 1,6-enyne cyclization or Pauson−Khand enyne cyclization.