Reactions Of Enynes Research Articles

Role of σ,π-Digold(I) Alkyne Complexes in Reactions of Enynes.

Gold(I) acetylide and σ,π-digold(I) alkyne complexes derived from one prototypical 1,6-enyne and from 7-ethynyl-1,3,5-cycloheptatriene have been prepared and structurally characterized. Their possible role in gold(I)-catalyzed cycloisomerizations has been studied by experiment and by DFT calculations. Gold(I) acetylides are totally unproductive complexes in the absence of Brønsted acids. Similarly, no cyclizations were observed by heating σ,π-digold(I) alkyne digold(I) at least up to 130 °C. Theoretical studies provide a rationale for the much lower reactivity of digold species in reactions of enynes.

ChemInform Abstract: Rapid Access to 2‐Methylene Tetrahydrofurans and γ‐Lactones: A Tandem Four‐Step Process.

AbstractThe reaction of enynals (I) with propynols (II) proceeds via hydrolysis, Knoevenagel condensation, Michael addition and Conia‐ene reaction to afford indanone‐fused 2‐methylene tetrahydrofurans (III), which are oxidized to α‐methylene γ‐lactones (IV).

Rapid Access to 2-Methylene Tetrahydrofurans and γ-Lactones: A Tandem Four-Step Process.

A one-pot tandem process involving hydrolysis, Knoevenagel condensation, Michael addition, and Conia-ene (HKMC) reactions has been developed for the rapid synthesis of indanone-fused 2-methylene tetrahydrofurans from the reaction of enynals and propynols. In this process, two rings and four bonds are generated with 100 % atom-economy and high step-efficiency. The resulting tetrahydrofurans were readily oxidized into α-methylene γ-lactones, which are one of the most important substructures in natural and bioactive compounds.

Rapid Access to 2‐Methylene Tetrahydrofurans and γ‐Lactones: A Tandem Four‐Step Process

AbstractA one‐pot tandem process involving hydrolysis, Knoevenagel condensation, Michael addition, and Conia‐ene (HKMC) reactions has been developed for the rapid synthesis of indanone‐fused 2‐methylene tetrahydrofurans from the reaction of enynals and propynols. In this process, two rings and four bonds are generated with 100 % atom‐economy and high step‐efficiency. The resulting tetrahydrofurans were readily oxidized into α‐methylene γ‐lactones, which are one of the most important substructures in natural and bioactive compounds.

Three-Component Coupling Reaction of Enynes, Carbonyls, and Organozinc Reagents

Three-Component Coupling Reaction of Enynes, Carbonyls, and Organozinc Reagents

Protection of the Gold(I) Catalyst by AsPh3 in Reactions of Enynes

AbstractNeutral gold complexes with hydrogen‐bond‐supported heterocyclic carbene (HBHC) and nitrogen acyclic carbene (NAC) ligands have been synthesized by the reactions of isocyanogold derivatives [AuCl(CNR)] with amines. Cationic [Au(carbene)(AsPh3)][SbF6] complexes have also been prepared. The catalytic activity of both types of complex (for the former, AgSbF6 is used to extract the halide ligand) in the skeletal rearrangement and methoxycyclization of enynes has been studied. The cationic complexes with AsPh3 are active but slower; advantageously, they do not decompose during the catalysis. In contrast, the catalysts formed in situ from the neutral halide complexes are very fast but undergo decomposition. An interesting trade‐off was found by adding substoichiometric amounts of AsPh3 (e.g., 10 mol‐%) relative to the gold catalyst {[Au(carbene)Cl] + AgSbF6}, which prevents or dramatically reduces the decomposition. This protecting ligand promises to prevent or minimize the undesired decomposition of gold catalysts.

Chemoenzymatic route to various spirocyclic compounds based on enantiomerically enriched tertiary allylic, homoallylic, and homopropargylic alcohols

A ring closing metathesis (RCM) reaction of dienes and an intramolecular Pauson–Khand (PKR) reaction of enynes derived from tertiary allyl, homoallyl, and homopropargyl alcohol backbones to afford the corresponding spirocyclic dihydrofuran and dihydropyrans and spirocyclic cyclopentenone pyrans, respectively, are described. Cyclopent-2-ene anchored tertiary allyl, homoallyl, and homopropargyl alcohols 1a–c have been efficiently resolved via enzymatic resolution with high ee (up to 90%) with 44%, 40%, and 43% chemical yields, respectively. Moreover, the cyclohex-2-ene anchored tertiary allyl, homoallyl, and homopropargyl alcohols 3a–c have also been resolved in the same manner with high ee (up to 97%) and in 42%, 45%, and 49% chemical yields. Enantiomerically enriched dienes derived from tertiary homoallyl alcohols yield the corresponding enantiomerically enriched spirocyclic dihydropyran derivatives via RCM with 74% and 78% chemical yields and with 90% and 97% ee, respectively. Moreover, enantiomerically enriched enynes derived from tertiary homoallyl alcohols afford the corresponding enantiomerically enriched cyclopentenone pyrans with spirocyclic motifs via PKR with 80% and 81% chemical yields, respectively, and as single diastereomers.

Platinum(II) Catalyzed Enantioselective Cycloisomerizations of 3‐Hydroxylated 1,5‐Enynes

AbstractThe enantioselective cycloisomerization of 3‐hydroxylated 1,5‐enynes into bicyclo[3.1.0]hexanones was investigated by using cyclometalated NHC‐platinum phosphoramidite complexes as pre‐catalysts. Several new complexes were prepared. They generate cationic, electrophilic PtII species that efficiently promote the cycloisomerization process. Enantiomeric excesses up to 81 % were obtained in the reactions of enynes with aryl‐substituted alkyne functions (8 examples, 70–81 % ee).

New nitrochromenylmethylidene-containing ruthenium metathesis catalyst

New Hoveyda-Grubbs type catalyst containing nitrochromenyl ligand is reported herein. The catalyst was tested in model RCM, CM and enyne reactions. Its activity was compared with that of commercially available complexes and with literature data for Grela catalyst. New catalyst appeared to be fast initiating, but less stable than other catalysts.

Utilization of Aldoses as a Carbonyl Source in Cyclocarbonylation of Enynes

The reaction of enynes with acetyl-masked aldoses in the presence of a rhodium(I) catalyst resulted in cyclocarbonylation, thus avoiding the direct use of carbon monoxide, to afford bicyclic cyclopentenones. In rhodium catalysis, aldoses serve as a carbon monoxide equivalent by donating their carbonyl moieties on the acyclic aldehyde form to enynes. A variety of aldoses, including D-glucose, D-mannose, D-galactose, D-xylose, and D-ribose, can be used as a carbonyl source. Using the method, a wide variety of enynes were cyclocarbonylated in 22-67% yields. An asymmetric variant also proceeded with moderate to high enantioselectivity.

ChemInform Abstract: Vinyl Radical Generation with Selenoborane and Its Application to Cyclization Reaction of Enynes.

Abstract Tris(methylseleno)- and tris(phenylseleno)boranes added to acetylenes to afford methylseleno- and phenylseleno-substituted Z -vinylselenides in high yields. The addition reactions proceeded by way of free radicals and were applied to cyclization reactions of enyne compounds. The radical cyclization provided pyrrolidine derivatives diastereoselectively.

Origins of regioselectivity and alkene-directing effects in nickel-catalyzed reductive couplings of alkynes and aldehydes.

The origins of reactivity and regioselectivity in nickel-catalyzed reductive coupling reactions of alkynes and aldehydes were investigated with density functional calculations. The regioselectivities of reactions of simple alkynes are controlled by steric effects, while conjugated enynes and diynes are predicted to have increased reactivity and very high regioselectivities, placing alkenyl or alkynyl groups distal to the forming C-C bond. The reactions of enynes and diynes involve 1,4-attack of the Ni-carbonyl complex on the conjugated enyne or diyne. The consequences of these conclusions on reaction design are discussed.

Missing cyclization pathways and new rearrangements unveiled in the gold(I) and platinum(II)-catalyzed cyclization of 1,6-enynes

Cyclopropyl metal carbenes formed in the 6- endo- dig cyclization may evolve to form seven-membered ring intermediates. This has been achieved for the first time by using highly electrophilic platinum(II) and gold(I) complexes. Gold(I) also triggers a remarkable rearrangement of certain enynes leading to complex cyclic systems. A new cationic platinacycle is described, which catalyzes skeletal rearrangements and other reactions of enynes at room temperature.

Prins Cyclizations in Au‐Catalyzed Reactions of Enynes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Rhodium‐Catalyzed Asymmetric Cyclization/Hydroboration of 1,6‐Enynes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Prins Cyclizations in Au‐Catalyzed Reactions of Enynes

Prins Cyclizations in Au‐Catalyzed Reactions of Enynes

Prins Cyclizations in Au‐Catalyzed Reactions of Enynes

Going for gold: AuI-catalyzed cyclizations of functionalized enynes lead to the ready assembly of tricyclic carbon skeletons that are present in a number of naturally occurring compounds. An alkenyl gold intermediate is formed in the cyclization of the enynes and can be trapped in 5-exo-dig or 6-endo-dig Prins reactions to form an additional CC bond. Z=C(CO2Me)2, NTs; R=H, Me, iPr.

Lewis Acid-Catalyzed [4 + 2] Benzannulation between Enynal Units and Enols or Enol Ethers: Novel Synthetic Tools for Polysubstituted Aromatic Compounds Including Indole and Benzofuran Derivatives

The reaction of enynals 1, including o-(alkynyl)benzaldehydes, and carbonyl compounds 2, such as aldehydes and ketones, in the presence of a catalytic amount of AuBr3 in 1,4-dioxane at 100 degrees C gave the functionalized aromatic compounds 3 in high yields. Similarly, the AuBr3-catalyzed reactions of 1 with acetal compounds 5 afforded the corresponding aromatic compounds 3 in good yields. On the other hand, when the reaction was carried out in the presence of a catalytic amount of Cu(NTf2)2 and 1 equiv of H2O in (CH2Cl)2 at 100 degrees C, the decarbonylated naphthalene products 4 were obtained selectively over 3. Benzofused heteroaromatic compounds, such as indole derivatives 13 and benzofuran derivatives 15, were also synthesized by using the present benzannulation methodology.

Skeletal Reorganization of Enynes Catalyzed by InCl3

[reaction: see text] The skeletal reorganization of enynes is achieved by the presence of InCl(3) as the catalyst. The reaction of enynes having a terminal acetylenic moiety proceeds in a stereospecific manner to give 1-vinylcycloalkenes. The reaction of enynes containing an alkyl group on the acetylenic terminal carbon resulted in a new type of skeletal reorganization to give 1-allylcycloalkenes, formation of which involves a double cleavage of the C-C double bond and the triple bond.

Rhodium-Catalyzed Asymmetric Cyclization/Hydroboration of 1,6-Enynes

[reaction: see text] Reaction of enyne 1 with catecholborane catalyzed by a 1:1 mixture of [Rh(COD)(2)](+)SbF(6)(-) and (S)-BINAP (5 mol %) followed by Pd-catalyzed arylation with p-IC(6)H(4)CF(3) gave benzylidenecyclopentane 5 in 65% yield with 88% ee. Rhodium-catalyzed asymmetric cyclization/hydroboration followed either by Pd-catalyzed arylation or by oxidation was applied to the synthesis of a number of chiral, nonracemic carbocycles and heterocycles.