Gold(I)-catalyzed one-pot reaction between 2-alkynylanilines and alkynols leading to the formation of C-3-substituted indoles: a case of formal carboamination of alkynes

A process involving gold(I)-catalyzed formal carboamination of alkynes for the synthesis of C-3-substituted indoles has been developed. The procedure utilizes easily accessible starting materials such as 2-alkynylanilines and alkynols. A series of C-3-functionalized indoles are accessible by using this one-pot strategy. Mechanistically, the reaction involves three catalytic cycles and each of them is essentially catalyzed by a single metal catalyst, that is, Ph₃PAuOTf.     

Pt(II)-catalyzed hydroarylation reaction of alkynes with pyrroles and furans

A Pt(II) catalyst showed a drastic effect on hydroarylation of alkynes with pyrroles and furans compared with Pd(OAc)₂ catalyst. The hydroarylation reactions proceeded smoothly under mild conditions to give double-hydroarylation products in good yields. Mono-adducts were formed only when the second hydroarylation was inhibited by steric hindrance of substrates or low reactivity of the mono-adducts.     

Regioselective synthesis of 3,3-bis(indolyl)propanoic acid derivatives by iron(III)-catalyzed hydroarylation of propynoic acid derivatives with indoles

Intermolecular hydroarylation of propynoic acid and its esters with indoles proceeded efficiently in acetic acid under a catalytic system of FeCl₃/3AgOTf and afforded the corresponding 3,3-bis(indol-3yl)propanoic acids and their esters in high yields. In the case of 2-methylindole, 3-indolylacrylic acid and its ethyl ester were obtained in high yields. This iron-catalyzed hydroarylation showed a high regioselectivity at the 3-position of indoles and a high utility for the synthesis of bis(indol-3-yl) compounds, which are important for biological and pharmaceutical fields.     

Reactions of indoles with mercury (II) salts

A number of mercurated indoles were prepared. Their spectroscopic data (UV,ir,^1H-NMR and13C-nmr) are reported. Our results contradict certain data appearing in previous reports on similar compounds. When heated in acetic acid mercurated compounds decomposed, although the products formed were not identical with those obtained earlier from the same substrates by the action of thallium(III) acetate in acetic acid. Reaction of l-methylindole-3-mercuriacetate with styrene in the presence of lithium tetrachloropalladate furnished a product which was tentatively assigned the structure 9-methyl-1,3-diphenyl-1, 2, 3, 4-tetrahydrocarbazole.     

A copper(II)-catalyzed protocol for modified Friedländer quinoline synthesis

2-Aminobenzyl alcohol reacts with an array of ketones in dioxane at 100 °C in the presence of a catalytic amount of CuCl₂ along with KOH under O₂ atmosphere to afford the corresponding quinolines in good yields. 2-Aminobenzyl alcohol is also oxidatively coupled and cyclized with various aldehydes by step-by-step procedure, an initial treatment of 2-aminobenzyl alcohol in the presence of CuCl₂ and KOH in dioxane under O₂ atmosphere and subsequent addition of aldehyde to the mixture followed by stirring under argon atmosphere, to give 3-substituted quinolines in moderate to good yields.     

Synthesis of bis(indolyl)alkanes by a site-selective gold-catalyzed addition of indoles to butynol derivatives

A new site-selective hydroarylation reaction of alkynes catalyzed by gold complexes and directed by an internal hydroxyl group has been developed. Thus, the treatment of 3-butyn-1-ol derivatives with indoles and a catalytic amount of an in situ formed cationic gold complex leads to the formation of bis(indolyl)alkane derivatives. Particularly interesting is the reaction with terminal alkynes as the double addition of the indol occurs at the terminal carbon of the triple bond. The reaction conditions are very mild and the final bis(indolyl)alkanes are obtained in high yields.     

Diastereoselective 2,3-diazidation of indoles via copper(II)-catalyzed dearomatization

The copper-catalyzed directed dearomatization of indoles with the assistance of directing groups has been developed for the synthesis of 2,3-diazido indolines with good yields and excellent diastereoselectivities in aqueous solution. The resultant 2,3-diazides can be smoothly converted to other functional groups, including vicinal diamines, triazoles and benzotriazoles, in a single step.     

Synthesis of 3-(2-nitroalkyl) indoles by reaction of 3-(1-arylsulfonylalkyl) indoles with nitroalkanes

Sulfonyl indoles act as effective precursors of vinylogous imino derivatives in the reaction with nitroalkanes under basic conditions leading to the corresponding nitro indoles in good yield. This procedure represents an effective option to the classical conjugate addition of indoles to nitroalkenes.     

Cu(I)/Cu(II)-catalyzed allylic amination of alkenes

Allylic hydrocarbons are selectively converted to the corresponding allyl amines in good to excellent yield by reaction with aryl hydroxylamines catalyzed by a 1:1 mixture of CuCl and CuCl₂ (10 mol %). Under these conditions unsymmetrical olefins react highly regioselectively with N-functionalization at the less substituted vinylic carbon. Trapping experiments indicate that a free nitrosoarene is not an intermediate in these reactions.     

Copper(II) chloride-catalyzed Glaser oxidative coupling reaction in polyethylene glycol

Polyethylene glycol was shown to be an environmentally benign reaction medium for the copper(II) salt -catalyzed Glaser coupling reaction of terminal alkynes. In particular, oxygen as the sole oxidant worked very well for arylacetylenes even in short reaction time. The product was easily separated by extraction and the catalytic system could be reused four times without significant loss of reactivity.     

W(II)-catalyzed hydroarylation of bicyclo[2.2.1]hept-2-ene by simple arenes

The tungsten(II) carbonyl compound (CO)₄W(μ-Cl)₃W(SnCl₃)(CO)₃ has been found to be a very effective catalyst for the hydroarylation of bicyclo[2.2.1]hept-2-ene (norbornene) conducted in arene solution at room temperature. Norbornene adducts with benzene, toluene, para-xylene, and mesitylene have been isolated and their structures have been unambiguously established by means of ¹H and ¹³C NMR spectroscopy. On the basis of ¹H NMR monitoring of several catalytic reactions, a possible mechanism involving coordination of norbornene to the W(II) atom and its activation has been proposed.     

Synthesis of indolylalkylphosphonates and 3-(1-diphenylphosphinoalkyl) indoles by reaction of 3-(1-arylsulfonylalkyl) indoles with phosphorus derivatives

Dialkyl phosphites as well as diphenylphosphine react with 3-(1-arylsulfonylalkyl) indoles under basic conditions leading to a formal substitution of the arylsulfonyl group through a reactive 3-alkylidene indole intermediate.     

Trisoxazoline/Cu(II)-catalyzed asymmetric intramolecular Friedel-Crafts alkylation reaction of indoles

Intramolecular Friedel-Crafts alkylation reaction of indoles catalyzed by trisoxazoline/copper(II) is described. This annulation provides an easy access to polycyclic indole derivatives with up to 90% ee in up to 99% yield.     

Hydroxyapatite-supported copper(II)-catalyzed azide-alkyne [3+2] cycloaddition with neither reducing agents nor bases in water

Copper(II)-exchanged hydroxyapatite, prepared by ion-exchanging of Ca(II) in calcium hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂] with Cu(NO₃)₂ at 70 °C in water, functions as a reusable heterogeneous catalyst with neither reducing agents nor bases for azide-alkyne [3+2] cycloaddition at 50 °C in water under air.     

Copper (II)-catalyzed regio- and stereoselective addition of H/P(O)R2 to alkynes

Cu(acac)₂ is the new universal catalyst for β-E regio- and stereoselective syn-addition of the H–P(O)-bond of diphenylphosphine oxide, H-phosphinates, dialkylphosphites to various alkynes in the synthesis of P(O)-containing alkenes. Without additives and ligands Cu(II)-compounds showed better results than CuI or Ni(acac)₂. The catalytic system developed is tolerant to typical organic functional groups present in the alkynes and to the nature of different substituents in the H–P(O)-compounds.     

Copper-mediated oxidative tandem reactions with molecular oxygen: synthesis of 2-arylbenzoxazinone derivatives from indoles

We developed an efficient method for the transformation of indoles by utilizing a copper catalyst and molecular oxygen as the oxidant. The transformation involves a tandem oxidative process of 2-arylindoles. Our reaction afforded a variety of N-benzoyl anthranilic acids and benzoxazinones. Our investigation revealed that the choice of solvent and additives is critical in these reactions.     

Catalytic hydroarylation of alkynes with arenes in the presence of FeCl3 and AgOTf

Hydroarylation of propiolic acids with various arenes in TFA proceeded efficiently in the presence of FeCl₃/AgOTf catalyst system. In the case of electron-rich arenes, the iron-catalyzed hydroarylation gave cinnamic acids in moderate to high yields. The hydroarylation of phenylacetylene was observed but the catalyst was not effective under the same conditions.     

Palladium-catalyzed reaction of aryl iodides with tertiary propargylic amides.: Highly substituted allenes through a regioselective carbopalladation/β-NPd elimination reaction

The palladium-catalyzed reaction of aryl iodides with tertiary propargylic amides affords highly substituted allenes. Best results have been obtained by using Pd(OAc)₂, ⁿBu₃N, HCOOH, and ⁿBu₄NCl or LiCl in DME at 100 °C. The reaction is highly regioselective and the carbopalladation step is controlled by the strong directing effect of the tertiary amide group.     

Synthesis of 3-perfluoroalkyl-substituted 1,2,4-triazinones through copper(I)-catalyzed interrupted click reaction

A Cu-catalyzed interrupted click reaction for the synthesis of 3-perfluoroalkyl-substituted 1,2,4-triazinones is developed. The reaction between the terminal alkynes with azides and pentafluoropropionic or heptafluorobutyric anhydride proceeds smoothly to afford the corresponding pentafluoroethylated or heptafluoropropyled products in good yields. This protocol is applicable to various types of substrates including arylacetylenes and aliphatic azides having electron-rich and electron-deficient groups. The broad substrate scope and functional group tolerance of the reaction makes this approach a practical method for the synthesis of valuable 3-perfluoroalkyl-substituted 1,2,4-triazinones. Some of the title compounds showed fungicidal activity against cucumber downy mildew (CDM).     

Platinum(II)-catalyzed intermolecular hydroarylation of unactivated alkenes with indoles

Ethylene, alpha-olefins, and vinyl arenes undergo platinum-catalyzed hydroarylation with substituted indoles in moderate to good yield.