Ruthenium-Catalyzed Transfer Hydrogenation of Alkynes: Access to Alkanes and (E)- or (Z)-Alkenes in Tandem with Pd/Cu Sonogashira Cross-Coupling

A complete reduction of alkynes using a combination of [RuCl2(p-cymene)]2, DTBM-SEGPHOS, and a paraformaldehyde/water system as the hydrogen source was developed, affording alkanes in 52-99% yields. In addition, the preparation of alkenes from terminal alkynes and aryl iodides by a tandem process of Pd/Cu-catalyzed Sonogashira reaction followed by Ru-catalyzed transfer hydrogenation is reported, affording alkenes in 38-99% yields. This multicatalysis proceeds via three consecutive reactions and can be extended further, as shown by adding an iodine-catalyzed cis-trans alkene isomerization step.