Gold-Catalyzed Oxidative Cyclization of 4‑Allenyl-1-ynes with 8‑Methylquinoline Oxide

Gold-catalyzed oxidative cyclizations of 4-allenyl-1-ynes with 8-methylquinoline oxide are described; diverse products are produced depending on the allenyl substituents. This reaction comprises initial formation of α-oxo gold carbenes that are attacked by allene to form allyl cation intermediates

[3 + 2]-Annulations of <i>N</i>‑Hydroxy Allenylamines with Nitrosoarenes: One-Pot Synthesis of Substituted Indole Products

In the presence of O₂ and an IPrCuCl additive (5 mol %), [3 + 2]-annulation reactions of <i>N</i>-hydroxyaniline with nitrosobenzenes in cold toluene form isoxazolidin-5-ol derivatives. Heating the same reaction mixture with DBU in toluene affords highly functionalized indole products efficiently. This method provides short synthesis of several bioactive molecules including WIN 48098, WIN 53365, and JWH 015

Gold-Catalyzed Oxidative Cyclization of 4‑Allenyl-1-ynes with 8‑Methylquinoline Oxide

Gold-catalyzed oxidative cyclizations of 4-allenyl-1-ynes with 8-methylquinoline oxide are described; diverse products are produced depending on the allenyl substituents. This reaction comprises initial formation of α-oxo gold carbenes that are attacked by allene to form allyl cation intermediates

Brønsted Acids Enable Three Molecular Rearrangements of One 3‑Alkylidene‑2<i>H</i>‑1,2-oxazine Molecule into Distinct Heterocyles

This work describes three different strategies to structurally rearrange one 3-alkylidene-2<i>H</i>-1,2-oxazine molecule into three distinct heterocycles using HOTf, propiolic acid, and silica gel, respectively. The mechanisms of these rearrangement reactions involve three independent routes, including (i) Brønsted acid catalysis, (ii) a synergetic action of Brønsted acids and anions, (iii) a surface-directed chemoselectivity

Two Distinct Cyclizations of 2‑Propenyl-1-ethynyl Benzenes with Aryldiazo Esters Using Au and Rh/Au Catalysts Respectively

This work reports the development of two catalytic cyclizations of 2-propenyl-1-ethynylbenzenes with aryldiazo esters. Cationic gold catalyst produces 2-substituted 3-alkenyl-1<i>H</i>-indenes with substrates over a reasonable scope. Our mechanistic study suggests that arydiazo esters attack at the cyclopropyl moieties of gold carbene intermediates, followed by skeletal rearrangement of resulting intermediates. In the presence of Rh₂(esp)₂ additive, the same gold catalyst alters the chemoselectivity of these reactants to afford tetrahydro-1<i>H</i>-cyclopropa­[<i>b</i>]­naphthalenes with excellent stereoselectivity. Herein, Rh­(II) catalyst catalyzed the reactions of the same 1,6-enynes with diazo species to form cyclopropenes initially, and a cationic Au­(I) catalyst allows their subsequent reactions with the tethered alkenes. Preferable <i>E</i>-selectivity and synergistic effects of Au/Rh catalysts are rationalized in a postulated mechanism

Gold-Catalyzed Reactions between Alkenyldiazo Carbonyl Species and Acetals

In the presence of catalyst IPrAuSbF₆ catalyst (IPr = 1,3-bis­(diisopropylphenyl)­imidazol-2-ylidene), alkenyldiazo carbonyl species react with organic acetals to give <i>E</i>-configured alkyl 3,5-dimethoxy-5-pent-2-enoates stereoselectively. This reaction sequence comprises an initial Prins-type reaction, followed by gold carbene formation

Oxidant-Dependent Chemoselectivity in the Gold-Catalyzed Oxidative Cyclizations of 3,4,6,6-Tetrasubstituted 3,5-Dien-1-ynes

A distinct chemoselectivity in the gold-catalyzed oxidative cyclization of 3,5-dien-1-ynes was observed when 3,5-dichloropyridine <i>N</i>-oxide replaced 8-methylquinoline <i>N</i>-oxide as the oxidant; the resulting cyclopentadienyl aldehydes were obtained in good yields. The altered chemoselectivity is attributed to a prior enyne cyclization in the presence of 3,5-dichloropyridine <i>N</i>-oxides. The use of <i>N</i>-iminopyridium ylide enables a similar iminocyclization reaction to give cyclopentadienyl imines efficiently. Our experimental data support a prior gold-catalyzed cyclization of 3,5-dien-1-ynes to form gold carbene, followed by the oxidation with <i>N</i>-oxide

Zn(II)- or Ag(I)-Catalyzed 1,4-Metathesis Reactions between 3‑En-1-ynamides and Nitrosoarenes

Catalyst-dependent metathesis reactions between 3-en-1-ynamides and nitrosoarenes are described. Particularly notable are the unprecedented 1,4-metathesis reactions catalyzed by Ag­(I) or Zn­(II) to give 2-propynimidamides and benzaldehyde derivatives. With 3-en-1-ynamides bearing a cycloalkenyl group, 1,4-oxoimination products were produced efficiently. We have developed metathesis/alkynation cascades for unsubstituted 2-propynimidamides and benzaldehyde species generated <i>in situ</i>, to manifest 1,4-hydroxyimination reactions of 3-en-1-ynes. Both 1,4-oxoiminations and 1,4-hydroxyiminations increase the molecular complexity of products

Oxidant-Dependent Chemoselectivity in the Gold-Catalyzed Oxidative Cyclizations of 3,4,6,6-Tetrasubstituted 3,5-Dien-1-ynes

A distinct chemoselectivity in the gold-catalyzed oxidative cyclization of 3,5-dien-1-ynes was observed when 3,5-dichloropyridine <i>N</i>-oxide replaced 8-methylquinoline <i>N</i>-oxide as the oxidant; the resulting cyclopentadienyl aldehydes were obtained in good yields. The altered chemoselectivity is attributed to a prior enyne cyclization in the presence of 3,5-dichloropyridine <i>N</i>-oxides. The use of <i>N</i>-iminopyridium ylide enables a similar iminocyclization reaction to give cyclopentadienyl imines efficiently. Our experimental data support a prior gold-catalyzed cyclization of 3,5-dien-1-ynes to form gold carbene, followed by the oxidation with <i>N</i>-oxide

Gold-Catalyzed [4 + 1]-Annulation Reactions between 1,4-Diyn-3-ols and Isoxazoles To Construct a Pyrrole Core

This work reports gold-catalyzed [4 + 1]-annulation reactions between 1,4-diyn-3-ols and isoxazoles or benzisoxazoles to yield pyrrole derivatives. The reaction chemoselectivity is controlled by an initial attack of an isoxazole at a less hindered alkyne to form gold carbenes, further inducing a 1,2-migration of a second alkyne group. A broad substrate scope of 1,4-diyn-3-ols, isoxazoles and even benzisoxazoles highlighted the reaction utility