Intramolecular addition of O−H and N−H bonds across carbon− carbon triple bonds to form 5-or 6-membered rings with exocyclic methylene groups for ether products and exocyclic methyl groups for imine products is catalyzed by (IPr)Cu(Me) (IPr = 1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene). In a competition study, the cyclization of primary amines was found to be faster than that of alcohols. Kinetic studies for the conversion of 4-pentyn-1-ol reveal that the catalytic reaction is first-order in copper catalyst and zero-order in alkynyl alcohol, and an Eyring analysis yields ΔH ‡ = 18.7(4) kcal/ mol and ΔS ‡ = −26(1) eu. The reaction of 5-phenyl-4-pentyn-1-ol provides (Z)-2-benzylidene-tetrahydrofuran in high yield and with quantitative stereoselectivity. Results from combined experimental and DFT studies are consistent with a mechanism that involves alkyne insertion into a Cu−O alkoxide bond followed by protonolysis upon reaction with free alkynyl alcohol.

Nucleophiles capable of four-electron donation (e.g., anilines, enolates) add to C2 of the N-acetylpyridinium (NAPy) ligand of TpW(NO)(PMe3)(NAPy)(OTf) and induce a Zincke−König-like ring scission to generate 3,4-coordinated acetamidotrienes or 1-azatrienes with 3Z,5E stereochemistry. This ring opening is driven by the enhanced π-acidity of the cyanine, relative to its purported dihydropyridine predecessor, which stabilizes the π-base {TpW(NO)(PMe3)}. X-ray data of the indoline-derived analogue (2) indicates that metal coordination disrupts the donor−acceptor (i.e., amide−iminium) conjugation in the cyanine ligand. Photolysis of 2 in the presence of indoline liberates a further derivatized cyanine.