| Alkynes, one of the simplest functional groups in chemistry, are fundamental building blocks in organic synthesis. With the recent advances in transition-metal catalysis and ligand design, the significance of the alkyne functionality is increasingly emphasized in the development of highly selective and atom-economical chemical transformations. The three topics described in this dissertation showcase the versatility of the alkyne functionality in transition metal catalysis.; In the presence of an oxovanadium complex, the carbon-carbon triple bond of propargylic alcohols can be transformed to vanadium allenoate complexes via a [3.3]-sigmatropic rearrangement. The allenoate complexes have been successfully utilized in a Mannich-type addition reaction. The initial inactivity has been overcome by modifying the vanadium complex to readily undergo transesterification with propargylic alcohols. Various propargylic alcohols and aryl N-methoxycarbonylimines participate in the reaction providing beta-aryl-alpha,beta-unsaturated ketones with good yield and complete Z-selectivity.; The palladium-catalyzed reductive cyclization of bis-alkynes has been successfully applied to the synthesis of (+)-streptazolin. The bis-alkyne precursor was prepared from D-mannitol acetonide via sequential diastereoselective alkynylide addition reactions. The palladium-catalyzed reductive cyclization provided the correct 1,3-diene unit selectively, which has been a major challenge in the synthesis of the molecule. The total synthesis was achieved in 11 steps from commercially available starting materials.; Two different metal-catalyzed reactions of alkynes have been utilized in an effort toward the total synthesis of (-)-laulimalide, a potent antitumor macrolide. The dihydropyran ring of the C1--C13 fragment was synthesized chemoselectively by rhodium-catalyzed cycloisomerization from the bis-alkyne substrate, via a vinylidene carbene complex. On the other hand, the second dihydropyran of the C14--C27 fragment was synthesized by ruthenium-catalyzed alkene-alkene coupling followed by palladium-catalyzed intramolecular allylic alkylation. The two main fragments have been combined by using another ruthenium-catalyzed alkene-alkyne coupling reaction, forming the complete carbon framework of laulimalide. |
