Cycloisomerization of Alkynols at Transition Metal Templates

Abstract

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

Metal Vinylidenes as Catalytic Species in Organic Reactions

“…[36] The first report of such a transformation dates back almost 15 years (Scheme 21). [37] Although the yields were modest, chromium, tungsten, and molybdenum carbonyl complexes were found to promote the stoichiometric cyclization of homopropargyl alcohol 64 to the corresponding Fischer carbene complexes.…”

A Synthesis of Densely Functionalized 2,3-Dihydropyrans Using Ring-Closing Metathesis and Base-Induced Rearrangements of Dihydropyran Oxides

“…The residue is purified by flash chromatography on silica to give 16 (0.21 g, 78%). Ϫ LRMS (EI ); m/z: 243 (M ϩ Ϫ 1, 2%), 137 (100), 91 (20). [74] Obtained from dihydrofuran oxide 10c (0.32 g, 1.7 mmol).…”

“…The cyclization of acetylenic alcohols at a metal template yields 2,3-dihydrofurans or 2,3-dihydropyrans, either directly [19] or via a carbene complex intermediate, which is subsequently cleaved by action of a base. [20] Alternatively, ring-closing metathesis of appropriately substituted enol ethers gives cyclic enol ethers related to glycals; however, use of the conveniently accessible GrubbsЈ catalyst is rather limited in these cases. [21Ϫ23] In the course of our studies directed towards the cleavage of conformationally rigid dihydropyran oxides by nucleophiles, [24] we investigated the base-promoted rearrangement of these substrates with a view towards the synthesis of 2,3-dihydropyrans and -furans.…”

Constructing Molecular Complexity from Alkynol Derivatives: A Journey from Fischer Carbene Complexes to Tandem Catalysis with Gold and other Carbophilic Lewis Acids

“…As previously commented, alkynol derivatives can be converted into Fischer-type carbene complexes under appropriate conditions (see Scheme 1, pathway a). 5 The excellent work developed by F. E. McDonald in this field should be remarked upon at this point. 6 Thus, we considered that alkynol derivatives, such as 7, should react in the presence of group 6 derived complexes M(CO) 5 ·L (M = Cr, Mo, W; L = labile ligand) to give Fischer carbene complexes 4 via π-complexes 8 (Scheme 3).…”

“…For this purpose, we needed to work with a catalyst derived from a group 6 metallic pentacarbonyl species. However, it should be noted that group 6 metallic pentacarbonyl species M(CO) 5 are unstable and need to be stabilized by an additional ligand to form the hexacoordinated species M(CO) 5 ·L, where ligand L is usually an amine (e.g., Et 3 N) or an ether (e.g., THF). It is also important to note that these M(CO) 5 ·L species are usually generated by the irradiation (350 nm) of a solution of the corresponding hexacarbonylmetal [M(CO) 6 ] in the presence of the ligand.…”