Light‐Driven Alkyne <i>gem</i>‐Hydrogenation: An Intramolecular Approach to <i>Hoveyda–Grubbs</i> Catalysts

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