Transition-metal-catalyzed alkyne functionalization is widely utilized in organic synthesis allowing the assembly of carbon-carbon and carbon-heteroatom bonds with high regio- and stereocontrol. Despite broad utility, current methods are limited to 1,2-addition or alkynylation. A new reaction manifold, geminal addition (1,1-addition) of alkynes, will expand the versatility of alkynes as useful building blocks for organic synthesis. This thesis describes geminal addition of alkynes via metal vinylidene mediated catalysis, where both heteroatom and carbon nucleophiles readily participate in the cyclization and three-component coupling processes.

Chapter 2 describes hydrative cyclization of 1,5-enynes under the catalysis of trinuclear ruthenium complex, [Ru₃Cl₅(dppm) ₃]PF₆, where cyclopentanone derivatives are synthesized from terminal alkynes tethered with α,β-unsaturated ketones, esters, aldehydes and nitriles. Chapter 3 discusses the three-component coupling reaction catalyzed by mononuclear ruthenium complex, [RuCl₂(dppm)(CH ₃CN)₂], to construct 1,4-dicarbonyl compounds via hydrative addition of alkynes to α,β-unsaturated ketones. In Chapter 4, arylative and alkenylative cyclization of 1,5-enynes is described, where rhodium diene complex, [Rh(OH)(COD)]₂, catalyzes geminal carbometalation of alkynes with organoboronic acids to synthesize cyclopentene derivatives. These three substantially different but conceptually coherent examples have demonstrated gemeinal addition of alkynes to be a general alkyne functionalization method that may find broad utility in organic synthesis.