Stereodivergent Alkyne Reduction by using Water as the Hydrogen Source

Article abstract of DOI:10.1002/chem.201803147

A homogeneous Pd-catalyzed stereodivergent reduction of alkynes to Z and E alkenes by using H₂O as the H₂ source is presented. Mediated by a diboron reagent, the transfer hydrogenation has been accomplished to yield the desired geometrical isomer by rational ligand selection. The switchable stereoselectivity achieved using simple phosphine ligands is generally excellent. D₂O has also been used as a D₂ source for synthesizing the corresponding deuterated olefins. Supported by a gram-scale synthesis, the reaction can easily be scaled up making it an efficient way to prepare alkenes commercially as well. Mechanistic studies suggest formation of H?PdL₂?OAc as the crucial step leading to the presence of two pathways involving H?Pd?B(OR)₂ and molecular H₂ as active intermediates.