Cycloisomerization of Alkynols at Transition Metal Templates

Abstract

The metal‐assisted cycloisomerization of ω‐alkynols to oxacycloalkylidene complexes is reviewed. A variety of low‐valent coordinatively unsaturated transition metal templates from group 6 to 10 mediate the cyclization of ω‐butynols, ‐pentynols, and ‐hexynols to give the corresponding oxacycloalkylidene complexes. In some cases kinetic hydroxyalkylvinylidene complex intermediates can be isolated and characterized.

Metal Vinylidenes and Allenylidenes in Catalysis: Applications in Anti‐Markovnikov Additions to Terminal Alkynes and Alkene Metathesis

“…vinylidene metal intermediates is well documented for Group 6-10 transition metals. [93] The catalytic version, illustrated by the endo cyclization of 3-and 4-alkyn-1-ols to give cyclic five-and six-membered enol ethers has been extensively studied, especially with molybdenum [94] and tungsten [95,96] carbonyl promoters (Scheme 12). [97,98] [Mo(CO) 6 ], [W(CO) 6 ], [W(CO) 5 (thf)], and [W(CO) 5 (Et 3 N)] are the most commonly used catalyst precursors, and photochemical activation is often used to generate the active promoters.…”

Ruthenium‐Catalyzed Reactions—A Treasure Trove of Atom‐Economic Transformations

“…(1), path B], on the other hand, proceeds under extremely mild conditions, but unfortunately these complexes were generally too stable to be synthetically useful. [10][11][12][13][14][15][16] The work disclosed by Bruce and co-workers in which various ruthenium vinylidene complexes (e.g. 2) were reportedly synthesized from [CpRu(PPh 3 ) 2 Cl] (1) [Eq.…”

“…The pyridine species is thought to undergo ligand exchange with one phosphine ligand, thereby placing the heterocycle proximal to the vinylidene moiety and thus enabling regioselective alkenylation [Eq. (14)]. Evidence for this mechanism was found by switching to a bidentate phosphine, dppe, which led to no alkenylation.…”

Reactions of Alkenyl Fischer Carbene Complexes with Ketene Acetals: Formation of Alkynes

“…[12] This process is most often employed in the forward direction as a method of preparing vinylidene complexes from terminal alkynes. [12,13] However, the reverse process has been investigated to some extent as a method for the preparation of alkynes. [14] Other than terminal alkynes (Z = H), the formation of vinylidene complexes has been observed with alkynes where Z is trialkylsilyl, [15] trialkyltin, [16] thioethers, [17] iodide [18] and an ester.…”