Light‐Driven Alkyne gem‐Hydrogenation: An Intramolecular Approach to Hoveyda–Grubbs Catalysts

The light‐driven gem ‐hydrogenation of internal alkynes in the presence of [(NHC)(η 6 ‐cymene)RuCl 2 ] generates discrete ruthenium carbene complexes. When applied to appropriately designed enyne substrates, the reactive intermediates thus formed will engage the tethered olefin in metathetic ring closure while splitting off a Hoveyda–Grubbs ‐type complex as secondary carbene. This unconventional approach to these classical catalysts for olefin metathesis rivals existing methodology in that it is safe, short, phosphine‐free, and uses readily available starting materials.