Copper-Catalyst-Controlled Site-Selective Allenylation of Ketones and Aldehydes with Propargyl Boronates

A practical and highly site-selective copper-PhBPE-catalyst-controlled allenylation with propargyl boronates has been developed. The methodology has shown to be tolerant of diverse ketones and aldehydes providing the allenyl adducts in high selectivity. The BPE ligand and boronate substituents were shown to direct the site selectivity for which either propargyl or allenyl adducts can be acquired in high selectivity. A model is proposed that explains the origin of the site selectivity.