Disubstituted Alkyne Research Articles

Total Syntheses of (−)-Lycoricidine, (+)-Lycoricidine, and (+)-Narciclasine via 6-exo Cyclizations of Substituted Vinyl Radicals with Oxime Ethers

The development of an approach to the total synthesis of the title alkaloids is described. The approach utilizes as the key strategic element a stereoselective 6-exo radical cyclization of a vinyl radical to an O-benzyloxime radical acceptor group. The vinyl radical was itself generated by regioselective addition of phenylthiyl radical to a disubstituted alkyne. The regiochemical issues of such additions, which result in different outcomes with tri-n-butylstannyl radicals and phenylthiyl radicals, are discussed. The first such synthesis described, that of (−)-lycoricidine, proceeded in 14 steps and 11% overall yield from 10 and served to develop the radical chemistry required. A second-generation synthesis, this time of the natural (+) enantiomer, was developed using insights gleaned from the first study and proved much more efficient, providing the target alkaloid in nine steps and 44% overall yield. This approach was then employed in the more demanding case of (+)-narciclasine. Several problems arising ...

Reactions of dinuclear and polynuclear complexes XIX. Rearrangements of terminal or disubstituted alkyne ligands present in homo- and heterodinuclear complexes of cobalt and molybdenum during reactions with molybdenum and cobalt carbonyl compounds: formation of trinuclear and tetranuclear clusters

The dicobalt alkyne complex [Co 2( μ-PhCCH)(CO) 6] 1a reacted with [Mo 2( η 5-C 5H 5) 2CO) 4] in refluxing tetrahydrofuran (THF) to give the μ 3-alkylidyne trinuclear cluster [Co 2Mo( η 5-C 5H 5)( μ 3-CCH 2Ph)(CO) 8] 3 as the major product. Possible routes to the formation of 3 have been investigated. Among the identified minor products from this reaction were [CoMo 2( η 5-C 5H 5) 2( μ 3-CCH 2Ph)(CO) 7] 4, [Co 2Mo 2( η 5-C 5H 5) 2( μ 4-PhC 2H)( μ-CO) 4(CO) 4] 5 and [Co 3Mo( η 5-C 5H 5) 2( μ 4-PhC 2H)( μ-CO) 2(CO) 5] 6. In contrast, when the related dicobalt complexes [Co 2( μ-CF 3CCR) (CO) 6] (R=CF 3 ( 1b), H ( 1c)), which contain alkynes with more strongly electron-withdrawing substituents, were heated with [Mo 2( η 5-C 5H 5) 2(CO) 4] in THF only mixed-dinuclear complexes [( η 5-C 5H 5)(CO) 2Mo( μ-CF 3C 2R)Co(CO) 3](Mo–Co) (R=H ( 7a), CF 3 ( 7b)) were formed. The reaction of the mixed-dinuclear complex 7b with [Co( η 5-C 5H 5)(CO) 2] led to the mixed-tetranuclear butterfly cluster [Co 2Mo 2( η 5-C 5H 5) 3( μ-CO)(CO) 3] 8. The thermal reaction of 1b with the phosphido compound [Mo 2( η 5-C 5H 5) 2( μ-CO)( μ-PPh 2) 2] gave rise to a single product, [Mo 2( η 5-C 5H 5) 2( μ-PPh 2){ μ-PPh 2Co 2( μ-CF 3C 2CF 3)(CO) 5}(CO) 2] 9, in which a phenyl ring of the ( μ-phosphido)dimolybdenum moiety is π-bonded to one of the two cobalt atoms. Spectroscopic data for the new complexes are discussed.

Reactivity of a two heteroatom stabilized anionic chromium (0) carbene complex towards a mono- and a disubstituted alkyne: New synthesis of γ-aminobutenolides and formation of a novel oligomer chromium (0) complex

The reaction of the chromium anionic carbene complex 1 towards diphenylacetylene and phenylacetylene is reported. In the former case the synthesis of γ-functionalized butenolides results after demetallation of the chromium complex 2 and the latter leads to the formation of a novel oligomer chromium complex 5. These complexes were characterized by mass spectrometry, IR and 1H and 13C NMR spectroscopies and their structures were confirmed by single-crystal X-ray analysis.

Reactions of a Dicarbenium Fulvalenyl Complex with Aromatic Nucleophiles and Synthesis of (μ-Alkyne)(fulvalenyl)tetracarbonyldimolybdenum Compounds: A Structure−Reactivity Relationship

The compound [FvMo2(CO)4(μ-η3:η3-CH2C⋮CCH2)][BF4]2 (3) reacts with weak nucleophiles to give the related carbenium complexes [FvMo2(CO)4(μ-η2:η3-CH2C⋮CCH2Nu)][BF4] (Nu = −C6H4OH, −C6H4OMe), where attack occurs exclusively on one carbenium center (−CH2+). Subsequent treatment by NaBH4 reduces the second carbenium center (−CH2+) to yield the disubstituted alkyne fulvalenyl adducts. The difference in reactivity between 3 and the analogous dicarbenium Cp system [Cp2Mo2(CO)4(μ-η3:η3-CH2C⋮CCH2)][BF4]2 is attributed to the fulvalene effect.

Rearrangement and Scission of Terminal Alkynes in Dimolybdenum Complexes on Reaction with Ruthenium Carbonyl: Formation of Trinuclear Vinylidene and Hexanuclear Bis(alkylidyne) Clusters

The reaction of the dimolybdenum alkyne complexes Mo2(CO)4(μ-R1C⋮CR2)Cp2 (Cp = η-C5H5; R1= H, R2 = H, Me, Ph, CO2Me; 1a−d) with Ru3(CO)12 in refluxing toluene or heptane affords reasonable yields of the orange μ3-vinylidene clusters [Mo2Ru(μ3-CCHR2)(CO)7Cp2] (2a−d). The crystal structure of Mo2Ru(μ3-CCHMe)(CO)7Cp2 (2b) has been determined and shows that the metal triangle is capped by a vinylidene ligand which is formally σ-bound to the two molybdenum atoms and π-bound to the ruthenium. Low to moderate yields of the blue-turquoise hexanuclear bis(alkylidyne) clusters Mo2Ru4(μ3-CR1)(μ3-CR2)(CO)12Cp2 (3a−d) are formed in addition to the vinylidene clusters, especially if the reaction is carried out in heptane. The synthesis of 3a is particularly noteworthy, as it represents the first example of the scission of ethyne into two methylidyne fragments on a metal cluster. The disubstituted alkyne complex 1e (R1 = R2 = Me) leads to the corresponding hexanuclear cluster 3e in either solvent, but complexes of bulki...

Novel Synthesis of Disubstituted Alkyne Using Molybdenum Catalyzed Cross-Alkyne Metathesis

Abstract A novel disubstituted alkyne synthesis was developed using molybdenum catalyzed cross-alkyne metathesis by Mortreux’s catalyst [Mo(CO)6-p-ClC6H4OH]. The reaction was carried out using Mo(CO)6 (5 mol% for total amounts of alkynes) and p-ClC6H4OH (1 equiv.) in the presence of an excess amount of another alkyne (3∼11 equiv.) in refluxing toluene.

Hexasubstituted benzenes by alkyne cyclotrimerization

Rhodium octanoate is shown to be an effective catalyst for the cyclotrimerization of a disubstituted alkyne.

Organochromium π-complexes—VIII. Reactions of the (η 5-Me 5C 5)Cr-system with 1,3-dienes and alkynes

Cp*(η 4-1,3-diene)Cr compounds have been prepared either by reacting Cp*(η 3-C 3H 5) 2Cr with a diene or by reducing Cp*Cr(THF)Cl 2 with activated-Mg in the presence of the diene. These coordinatively and electronically unsaturated species readily form adducts with CO or P-donor ligands. The reaction of Cp*(η 4-1,3-C 4H 6)Cr with further butadiene leads to the formation of Cp*(η 3,η 3-octadienediyl)Cr which in turn reacts with a disubstituted alkyne (RC 2R) with addition to the 2,7-positions of the octadienediyl chain to give Cp*(η 1,η 2,η 1-R 2C 10H 12)Cr species. The crystal structures of representative compounds have been established by X-ray diffraction.

Chemistry of Heterometallic Cluster Compounds Prepared by Condensation of Group 6 Metal Acetylide and Group 8 Binary Carbonyl Complexes

AbstractThe chemistry of trinuclear and tetranuclear heterometallic acetylide complexes, LWOs3(CO)11(CCR) and LWM2(CO)8(CCR), L = Cp and Cp*; M = Os and Ru, is presented. Included in this account are syntheses, characterization and reactivity, with a particular focus on reactions with disubstituted alkyne molecules. The reactivity and fluxionality of these acetylide complexes provides a plausible model for ligand‐mediated metal‐core rearrangement and the transformation of small organic molecules on catalytic metal surfaces.

ChemInform Abstract: Coupling Reactions of Aryl and Heteroaryl Halides with a Trimethylsilylethynylpyrazine.

Abstract2‐Chloro‐3,6‐diisobutylpyrazine (I) reacts with trimethylsilylacetylene (II) in the presence of a Pd catalyst and potassium acetate to form the disubstituted alkyne (III).

Studies of the synthesis, structure, and reactivity of a tetranuclear mixed-metal imido cluster, (η5-C5H5)WRu3(CO)9(µ-NPh)(CCPh)

The title complex (η5-C5H5)WRu3(CO)9(µ-NPh)(CCPh), containing a bridging imido ligand and a µ4-η2-acetylide ligand, has been prepared by means of the condensation between (η5-C5H5)W(CO)3CCPh and Ru3(CO)10(µ3-NPh), and its reactions with dihydrogen and disubstituted alkyne ligands are presented; the products have been fully characterized by spectroscopic methods and X-ray diffraction studies for two complexes.

Synthesis of naphthoquinone antibiotics by intramolecular alkyne cycloaddition to carbene-chromium complexes

The reaction of carbene-chromium complexes with alkynes provides a direct route to naphthoquinone derivatives and is the key step in a new approach to the isochromanone antibiotics exemplified by deoxyfrenolicin ( 1) and nanaomycin A ( 2). While the regioselectivity of intermolecular addition of the appropriate unsymmetrical disubstituted alkyne is unfavourable, two successful approaches have been developed. Allylacetylene reacts with methoxy-( o-methoxyphenyl)methylidene-Cr(CO) 5 with high regioselectivity. Bromination, lithiation, and reaction with acetaldehyde produced the desired precursor. Alkoxypalladation led to pyran ring formation and introduction of the acetate side chain. Following earlier procedures, nanaomycin A ( 2) was produced. A more convergent alternative involved intramolecular cycloaddition of an alkyne with the alkylidene-chromium unit. A series of model cyclizations established the feasibility and an alkyne with an ethylene glycol side chain was prepared. The ethylene glycol unit serves as the tether to hold the alkyne in place for cyclization and allows easy removal at a later stage. Deoxyfrenolicin ( 1) was produced in a highly convergent and efficient process.

Synthesis and Spectroscopic Studies of Some New Copper (I) Halide Adducts of Disubstituted Alkynes and Dimethylformamide

Abstract Eight copper (I) bromide and chloride complexes with disubstituted alkynes, RR'C(OH) CECX, (R,R' = Me or Et; X = Br or Cl), and dimethylformamide (DMF) were prepared and characterised. In all cases, the molar ratio of copper to disubstituted alkyne and DMF was 4:1:2. Elemental analysis and spectral data suggest that the disubstituted alkyne is coordinated to copper via a two-electron three centre bond.

Study of direction and selectivity of hydrogenation of acetylenic hydrocarbons in presence of palladium chloride-dimethylsulfoxide complex

1. The palladium chloride-dimethylsulfoxide complex catalyzes the hydrogenation of the C≡C bond. The reaction is zero order in the substrate, and its rate is independent of the length of the hydrocarbon chain of the substituent. 2. A monosubstituted alkyne is reduced at a slower rate than a disubstituted alkyne, but it is saturated first in a mixture of the two, since it is more strongly coordinated in the complex. 3. The alkynes are hydrogenated in steps, with a high selectivity and stereospecificity. 4. Diphenylacetylene is not hydrogenated in steps, by a different mechanism, with the formation of diphenylethane.