Rapid access to pyrazolo[3,4-c]pyridines via alkyne annulation: limitations of steric control in nickel-catalyzed alkyne insertions

Polyfunctionalized pyrazolo[3,4-c]pyridines were readily prepared by the annulation of alkynes with tert-butyl 4-iodopyrazolocarboximines. The reaction was found to be catalyzed by both NiBr2(PPh3)2/Zn or PdCl2(PhCN)2 to yield complex heterocycles in good to moderate yields. Annulation using nickel catalysis was found to be regio-random, implying that steric control in nickel-catalyzed alkyne insertion has limitations based on the character of the Ni-C bond in the pre-insertion complex.     

Regioselective synthesis of indoles via reductive annulation of nitrosoaromatics with alkynes

[reaction: see text] Indoles are produced regioselectively and in moderate yields by two new processes: (a) from the [CpRu(CO)2]2-catalyzed reaction of nitrosoaromatics (ArNO) with alkynes under carbon monoxide and (b) in a two-step sequence involving the (uncatalyzed) reaction of ArNO with alkynes, followed by reduction of the intermediate adduct.     

Highly active molybdenum-alkylidyne catalysts for alkyne metathesis: synthesis from the nitrides by metathesis with alkynes

Terminal nitrido complexes NMo(OC(CF3)2Me)3 (4), NMo(OC(CF3)2Me)3(NCMe) (4-NCMe), and NMo(OC(CF3)3)3(NCMe) (5-NCMe) react irreversibly with 3-hexyne at elevated temperature in hydrocarbon solution to form the corresponding propylidyne complexes EtCMo(OC(CF3)2Me)3 (3) and EtCMo(OC(CF3)3)3 (6), long known as exceptionally active catalysts for alkyne metathesis. The propylidyne complexes are isolated as the more readily crystallized 1,2-dimethoxyethane (DME) adducts for convenience; 3-DME is isolated in 61% yield on a multigram scale.     

One-pot synthesis of 2,4-disubstituted quinolines via silver-catalyzed three-component cascade annulation of amines,alkyne esters and terminal alkynes

Described herein is a new and general method for one-pot synthesis of 2,4-disubstituted quinolines via silver-catalyzed [3?+?1?+?2] annulation of simple amines, alkyne esters and terminal alkynes. The versatile transformation might initiate with the facile formation of the enamine species with the feature of good to excellent yields, exclusive regioselectivity, and excellent substrate/functional group tolerance.     

Direct synthesis of 3-arylindoles via annulation of aryl hydroxylamines with alkynes

3-Arylindoles are produced in moderate to excellent yields from the reaction between aryl hydroxylamines and alkynes catalyzed by 10 mol % iron(II) phthalocyanine [Fe(Pc)]. Terminal and internal alkynes afford 3-aryl substituted indoles exclusively. Electron-donating and -withdrawing groups are tolerated on the aryl hydroxylamine. A few bioactive indoles are synthesized as well as several new indoles using this one-step intermolecular annulation procedure.     

Ruthenium-catalyzed annulation of alkynes with amides via formyl translocation

The first example of Ru-catalyzed intramolecular annulation of alkynes with amides via formyl translocation has been developed, which provides an efficient approach for the synthesis of 1H-indole-3-carbaldehydes.     

Regioselective one-step synthesis of 4-fluoroalkylated isoquinolines via carbopalladation reaction of fluorine-containing alkynes

[reaction: see text] The palladium-catalyzed annulation reaction of fluoroalkylated alkynes with various 2-iodobenzylidenamines was investigated. In the presence of a catalytic amount of Pd(PPh3)4, the reaction took place smoothly to give the corresponding 4-fluoroalkylated isoquinoline in high yield as a single isomer. No other regioisomer was detected.     

Coupling of enamides with alkynes or arynes for synthesis of substituted pyridines and isoquinolines via amide activation

A novel and general procedure for Cu-catalyzed coupling of enamides with alkynes to synthesize substituted pyridines was developed. The chemistry was allowed to extend to the synthesis of substituted isoquinolines by coupling of enamides with arynes under transition-metal-free conditions.     

A novel and direct synthesis of indoles via catalytic reductive annulation of nitroaromatics with alkynes

Indoles are produced regioselectively and in moderate yields from the reactions of nitroaromatics with alkynes catalyzed by [CpM(CO)2]2 (1; [(eta 5-C5H5)Fe(CO)2]2; [(eta 5-C5Me5)-Fe(CO)2]2; [(eta 5-C5Me5)Ru(CO)2]2) under carbon monoxide.     

Palladium-catalyzed carbonylative annulation of terminal alkynes: synthesis of coumarins and 2-quinolones

o-Iodophenols and o-iodoaniline derivatives react with terminal alkynes under 1 atm of CO in the presence of pyridine and catalytic amounts of Pd(OAc)₂ to generate coumarins and 2-quinolones, respectively, as the only products. Terminal alkynes bearing alkyl, aryl, silyl, hydroxyl, ester and cyano substituents are effective in these processes affording the desired products in moderate yields. The formation of coumarins and 2-quinolones in this process is in stark contrast with all previously described palladium-catalyzed reactions of o-iodophenols or o-iodoanilines with terminal alkynes and CO, which have afforded chromones and 4-quinolones. Moreover, under our reaction conditions terminal alkynes insert into the carbonpalladium bond instead of undergoing a Sonogashira-type coupling as confirmed by an isotope labeling experiment.     

Highly efficient gold-catalyzed atom-economical annulation of phenols with dienes

[reaction: see text] A highly efficient annulation of phenols and naphthols with dienes was developed by using a combination of AuCl(3)/AgOTf as catalyst. The annulation generated various benzofuran derivatives under mild conditions rapidly.     

Stereoselective synthesis of enynes by nickel-catalyzed cross-coupling of divinylic chalcogenides with alkynes

(Z,Z)- and (E,E)-divinylic selenides and telurides undergo direct coupling with terminal alkynes in the presence of a nickel/CuI catalyst at room temperature to give (Z)- and (E)-enyne systems in good yields and with complete retention of configuration.     

Visible-light-induced synthesis of benzothiophenes and benzoselenophenes via the annulation of thiophenols or 1,2-diphenyldiselane with alkynes

An effective metal-free photoredox-mediated tandem addition/cyclization reaction of thiophenols or 1,2-diphenyldiselane with alkynes leads to 2,3-disubstituted benzothiophenes and benzoselenophenes. Blue light irradiation of the organic dye, Mes-Acr-Me⁺, initiates the photoredox catalysis. A series of functional groups could be tolerated under ambient conditions, and good to excellent yields were generated.     

A first regioselective synthesis of 3-fluoroalkylated benzofurans via palladium-catalyzed annulation of fluorine-containing internal alkynes with variously substituted 2-iodophenol

The palladium-catalyzed annulation reaction of a variety of fluorine-containing internal alkynes with 2-iodophenol derivatives was investigated. The use of P(t-Bu)₃ as a ligand on palladium was found to be crucial in this annulation reaction, resulting in the exclusive formation of 3-fluoroalkylated benzofurans in high yields. ¹⁹F NMR analysis of the reaction mixture revealed that the addition of phenol to the fluoroalkylated alkynes was followed by intramolecular Heck reaction, giving to the corresponding 3-fluoroalkylated benzofurans.     

Diversity-oriented synthesis of fused pyran gamma-lactones via an efficient Pd-thiourea-catalyzed alkoxycarbonylative annulation

We reported herein a diversity-oriented synthesis of a range of fused pyran-gamma-lactones that was effected through a versatile Pd-thiourea complex-catalyzed intramolecular alkoxycarbonylative annulation.     

Palladium-catalyzed carbonylative annulation of internal alkynes: synthesis of 3,4-disubstituted coumarins

The palladium-catalyzed annulation of internal alkynes by o-iodophenols in the presence of CO results in exclusive formation of coumarins. No isomeric chromones have been observed. The best reaction conditions utilize the 2-iodophenol, 5 equiv of alkyne, 1 atm of CO, 5 mol % Pd(OAc)2, 2 equiv of pyridine, and 1 equiv of n-Bu4NCl in DMF at 120 degrees C. The use of a sterically unhindered pyridine base is essential to achieve high yields. A wide variety of 3,4-disubstituted coumarins containing alkyl, aryl, silyl, alkoxy, acyl, and ester groups have been prepared in moderate to good yields. Mixtures of regioisomers have been obtained when unsymmetrical alkynes are employed. 2-iodophenols with electron-withdrawing and electron-donating substituents and 3-iodo-2-pyridone are effective in this annulation process. The reaction is believed to proceed via (1) oxidative addition of the 2-iodophenol to Pd(0), (2) insertion of the alkyne triple bond into the aryl-palladium bond, (3) CO insertion into the resulting vinylic carbon-palladium bond, and (4) nucleophilic attack of the phenolic oxygen on the carbonyl carbon of the acylpalladium complex with simultaneous regeneration of the Pd(0) catalyst. This annulation process is the first example of intermolecular insertion of an alkyne occurring in preference to CO insertion.     

A simple and efficient approach for the synthesis of 2-aminated quinazoline derivatives via metal free oxidative annulation

A simple and efficient approach for the synthesis of 2-aminoquinazoline derivatives in moderate to good yields. This reaction employs mild reaction conditions, is metal-free and utilizes readily available starting materials making it a more viable reaction for scale up synthesis and ligand diversity. Notably, this methodology allows for the synthesis of 2-aminoquinazolines using a free amine or cyclic amine enabling structural diversity and good atom economy.