Ruthenium-catalyzed transfer hydrogenation of alkynes

A complete reduction of alkynes using a combination of [RuCl$_2$(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.