Rh-Catalyzed Addition of Boronic Acids to Alkynes for the Synthesis of Trisubstituted Alkenes in a Biphasic System ? Mechanistic Study and Recycling of the Rh/m-TPPTC Catalyst

The versatile preparation of trisubstituted alkenes via selective Rh-catalyzed arylation of alkynes is described in water and in a water/toluene biphasic system. For hydrophobic alkyl alkynes, the reaction afforded either alkenes or dienes depending on the temperature and the solvent conditions. Aryl, heteroaryl, silylated and alkyl substituted alkynes reacted equally well with various boronic acids, leading regioselectively to functionalized alkenyl derivatives in high yields (65–99%). The mechanism was investigated in toluene/water mixture or water and involves a vinylrhodium complex. The efficient recycling of the Rh/m-TPPTC system is disclosed with excellent yield (92–96%) and purity of the alkene.