An efficient and selective synthesis of 2,5-substituted pyrroles by gold-catalysed ring expansion of alkynyl aziridines

A range of substituted alkynyl aziridines undergo a ring expansion to afford 2,5-substituted pyrroles under gold catalysis. While effective conditions can be generated from other gold sources, a combination of Ph₃PAuCl and AgOTs generate a catalyst system that provides extremely clean cycloisomerisation reactions requiring minimal work-up and purification.     

A simple and highly efficient solvent- and catalyst-free synthesis of novel N-sulfamoyl imines

The reaction of aldehydes with primary sulfonamides under solvent- and catalyst-free conditions is described. This method affords the N-sulfamoyl imines in short reaction times and high yields. Mild conditions, simplicity, inexpensive and easily available reagents, and absence of any auxiliary substances are some other advantages of this procedure.     

A facile and regioselective synthesis of 2,5-disubstituted pyrroles via gold-catalyzed cycloisomerization of acetylenylaziridines

Gold-catalyzed cycloisomerization reaction of acetylenylaziridines provides 2,5-disubstituted pyrroles in high yields. The presence of protic species accelerates the reaction rate and improves the yields of pyrrole products.     

A straightforward highly efficient Paal-Knorr synthesis of pyrroles

A straightforward simple synthesis of substituted pyrroles using bismuth nitrate-catalyzed modified Paal-Knorr method has been accomplished with an excellent yield. This method produces pyrroles with multicyclic aromatic amines.     

Copper-catalyzed synthesis of five-membered heterocycles via double C-N bond formation: an efficient synthesis of pyrroles, dihydropyrroles, and carbazoles

An efficient copper-catalyzed double C-N bond forming reaction using diiodides and nitrogen-centered nucleophiles including amides and carbamates is reported. The reactions proceed to afford di- or tri-substituted N-acylpyrroles, dihydropyrroles, and carbazoles in good to excellent yields when different diiodides such as 1,4-diiodo-1,3-butadienes, 1,4-dihalobut-1-enes, and 2,2′-diiodobiphenyls were employed, respectively. It is crucial to use CuI as the catalyst with the assistance of proper base and diamine ligand.     

A novel approach to 2-arylated quinolines: electrocyclization of alkynyl imines via vinylidene complexes

[reaction: see text] Alkynyl imines underwent [4 + 2] electrocyclization in the presence of 20 mol % W(CO)(5)(THF) to give 2-arylated quinolines in good yields. A deuterium labeling study suggests that the reaction proceeds via a tungsten vinylidene complex.     

An efficient and general synthesis of pyrroles

We have discovered that a wide range of 3-alkynyl-hydroxyalkanamine derivatives undergo 5-endo-dig cyclisations when exposed to silver nitrate supported on silica gel. Subsequent in situ dehydration of the resulting and sometimes isolable hydroxy-dihydropyrroles leads to pyrroles in essentially quantitative yields using this recoverable and reusable heterogeneous catalyst.     

A mild and efficient AgSbF6-catalyzed synthesis of fully substituted pyrroles through a sequential propargylation/amination/cycloisomerization reaction

Development of an efficient synthesis of fully substituted pyrroles via a sequential propargylation/amination/cycloisomerization was accomplished using AgSbF₆ as a catalyst. The one-pot three-component reaction of propargylic alcohols, 1,3-dicarbonyl compounds, and primary amines proceeds at a mild temperature, which prevents the formation of furan by-product. The reaction was also successfully applied to the more basic aliphatic amines with the addition of 1.1 equiv of acetic acid.     

Efficient synthesis of 2-mono- and 2,5-disubstituted furans via the CuI-catalyzed cycloisomerization of alkynyl ketones.

A mild, general, and efficient method for the synthesis of 2-monosubstituted and 2,5-disubstituted furans via the CuI-catalyzed cycloisomerization of alkynyl ketones was developed. It was demonstrated that furans containing both acid- and base-labile groups could be easily synthesized using this methodology. A plausible mechanism for this transformation is proposed.     

A novel synthesis of heterocycles from thiocarbohydrazides

Summary The reaction of thiocarbohydrazides1a and thiocarbazones1b with tetracyanoethylene (TCNE) afforded the thiazol, thiadiazole, thiazine, and thiadiazepine derivatives4–7. 2-Dicyanomethyleneindane-1,3-dione (CNIND) reacted with1a,b to give aminoindenopyrazolopyridazinone (12) and phenyl-1,2,3,4-tetraazacyclopentafluorene (13). The indazole and oxathiadiazole derivatives17 and19 were formed during the reaction of1b with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDO). 6,7-Dichloro-5-phenylpyrazolophthalazinol (21) was obtained from the reaction of1b with 2,3,5,6-tetrachloro-1,4-benzoquinone (CHL-p). The oxidative cyclization of thiodicarbazones2a–d with the above acceptors afforded the thiadiazole and thiadiazine derivatives8 and10.

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Eine neue Synthese von Heterocyclen aus Thiocarbohydraziden

Zusammenfassung Die Reaktion der Thiocarbohydrazide1a und der Thiocarbazone1b mit Tetracyanoethylen (TCNE) ergab die Thiazol-, Thiadiazol-, Thiazin- und Thiadiazepinderivate4–7. 2-Dicyanomethylenindan-1,3-dion (CNIND) liefert mit1a,b Aminoindenopyrazolopyridazinon (12) und Phenyl-1,2,3,4-tetraazacyclopentafluoren (13). Die Indazol- und Oxathiadiazolderivate17 und19 wurden durch Reaktion von1b mit 1,3-Dichlor-5,6-dicyano-1,4-benzochinon (DDQ) gebildet. 6,7-Dichlor-5-phenylpyrazolophthalazinol (21) wurde aus1b und 2,3,5,6-Tetrachlor-1,4-benzochinon (CHL-p) erhalten. Die oxidative Cyclisierung der Thiodicarbazone2a–d mit den obengenannten Akzeptoren ergab die Thiadiazol- und Thiadiazinderivate8 und10.

     

An efficient one-pot synthesis of tetra-substituted pyrroles

The three-component reaction of primary amines, dialkyl acetylenedicarboxylates and β-nitrostyrene derivatives in the presence of Iron(III) chloride afforded 1,2,3,4-tetra-substituted pyrroles in high yields. These reactions could precede via domino Michael addition/cyclization process.     

Mechanistically diverse copper-, silver-, and gold-catalyzed acyloxy and phosphatyloxy migrations: efficient synthesis of heterocycles via cascade migration/cycloisomerization approach

A set of cycloisomerization methodologies of alkynyl ketones and imines with concurrent acyloxy, phosphatyloxy, or sulfonyloxy group migration, which allow for the efficient synthesis of multisubstituted furans and N-fused heterocycles, has been developed. Investigation of the reaction course by way of employing 17O-labeled substrates allowed for elucidation of the mechanisms behind these diverse transformations. It was found that, while the phosphatyloxy migration in conjugated alkynyl imines in their cycloisomerization to N-fused pyrroles proceeded via a [3,3]-sigmatropic rearrangement, the analogous cycloisomerization of skipped alkynyl ketones proceeds through two consecutive 1,2-migrations, resulting in an apparent 1,3-shift, followed by a subsequent 1,2-migration through competitive oxirenium and dioxolenylium pathways. Investigations of the 1,2-acyloxy migration of conjugated alkynyl ketones en route to furans demonstrated the involvement of a dioxolenylium intermediate. The mechanism of cycloisomerization of skipped alkynyl ketones containing an acyloxy group was found to be catalyst dependent; Lewis and Br?nsted acid catalysts caused an ionization/SN1' isomerization to the allene, followed by cycloisomerization to the furan, whereas transition metal catalysts evoked a Rautenstrauch-type mechanistic pathway. Furthermore, control experiments in the cycloisomerization of skipped alkynyl ketones under transition metal catalysis revealed that, indeed, these reactions were catalyzed by transition metal complexes as opposed to Br?nsted acids resulting from hydrolysis of these catalysts with eventual water. Further synthetic utility of the obtained phosphatyloxy-substituted heterocycles was demonstrated through their efficient employment in the Kumada cross-coupling reaction with various Grignard reagents.     

Metal-free synthesis of alkynyl imines using an oxophosphonium-mediated approach at ambient temperatures

A metal-free approach was developed for the mild synthesis of N-aryl α-alkynyl imines from corresponding amide precursors for the first time. The electronic effects of substrates and the reaction mechanisms were investigated and discussed. This newly developed oxophosphonium-triggered one-pot multiple-step method presents the advantages of mild conditions, ease of operation and satisfactory efficiency.     

A mild and efficient synthesis of 4-quinolones and quinolone heterocycles

The cycloacylation of aniline derivatives to 4-quinolones in the presence of Eaton's reagent is described. This high-yielding methodology is applicable to a wide variety of functionalized anilines and requires milder conditions than those traditionally employed. This cyclization protocol is used to prepare a host of heterocycles and bis-quinolones and is characterized by relatively low reaction temperature and ease of product isolation.     

Gold-catalyzed synthesis of oxygen- and nitrogen-containing heterocycles from alkynyl ethers: application to the total synthesis of andrachcinidine

In this paper we report that homopropargylic ethers containing pendent oxygen or nitrogen nucleophiles react with electrophilic gold catalysts in the presence of water to form saturated heterocyclic ketones. Mechanistic studies demonstrated that the reactions proceed through a sequence of alkyne hydration, alkoxy group elimination, and intramolecular conjugate addition. Diastereoselectivities for tetrahydropyran and piperidine formation are very good to excellent. This method has been applied to an efficient total synthesis of the natural product andrachcinidine. Utilizing propargylic ether substrates rather than homopropargylic ethers promotes regioselective hydration of internal alkynes, thereby expanding the scope of products that can be accessed through this protocol.     

Straightforward synthesis of alkynyl imines via 1,2-elimination of α,α-dichloroketimines

Alkylation of α,α-dichloroketimines at the α-position with benzyl bromides afforded β-arylated α,α-dichloroketimines in good yields. The latter imines could be easily transformed to the corresponding alkynyl imines, a synthetically important class of compounds, via 1,2-elimination of HCl upon treatment with 2 equiv of sodium hydride in DMSO or potassium tert-butoxide in THF.     

A new and efficient one-pot synthesis of aromatic alkynyl ketones from aromatic esters

The reaction of aromatic esters with alkynyllithiums in the presence of lithium morpholinide and BF₃·OEt₂ gave aromatic alkynyl ketones in good yield (78-87%).     

Novel 2-pyridone synthesis via nucleophilic addition of malonic esters to alkynyl imines

[reaction: see text] A novel 2-pyridone synthesis via nucleophilic addition of malonic esters to alkynyl imines has been developed. The reaction of dialkylalkyl sodiomalonates with alkynyl imines provided 2-pyridones in good to excellent yields.