Mechanistic study of the solvent-controlled Pd(ii)-catalyzed chemoselective intermolecular 1,2-aminooxygenation and 1,2-oxyamination of conjugated dienes†
The Pd(II)-catalyzed intermolecular 1,2-aminooxygenation and 1,2-oxyamination between 2-aminophenol substrates and conjugated dienes give distinct chemoselectivities in MeCN and DMSO solvents. In the reaction system using the MeCN solvent, the nitrogen source first attacks the diene giving rise to the 1,2-aminooxygenation product; however, in the DMSO solvent, the oxygen source first attacks the diene, and the product resulting from 1,2-oxyamination is preferentially formed. To understand the origin of the chemoselectivity, the reaction mechanism was investigated using experimental studies and density functional theory (DFT) calculations. The results suggest that MeCN and DMSO solvents can both act as ligands and that the different coordination modes in MeCN and DMSO solvents result in differences between the free energy of the chemoselectivity-determining step; thus control of chemoselectivity is achieved.