FeCl3-SiO2 as a reusable heterogeneous catalyst for the synthesis of 5-substituted 1H-tetrazoles via [2+3] cycloaddition of nitriles and sodium azide

An efficient method for the preparation of 5-substituted 1H-tetrazole derivatives is reported using FeCl₃-SiO₂ as an effective heterogeneous catalyst. This method has the advantages of high yields, simple methodology, and easy work-up. The catalyst can be recovered by simple filtration and reused delivering good yields.     

Phosphine-catalyzed [4+2] cycloaddition of sulfamate-derived cyclic imines with allenoates: synthesis of sulfamate-fused tetrahydropyridines

Using n-PrPPh₂ as the nucleophilic catalyst, the [4+2] cycloaddition reaction of the sulfamate-derived cyclic imines with allenoates works efficiently to yield various sulfamate-fused tetrahydropyridines in high yields with excellent diastereoselectivities. Using amino acid-based bifunctional phosphine as chiral catalyst, an asymmetric [4+2] cycloaddition reaction was achieved, giving chiral sulfamate-fused tetrahydropyridines in high yields with good enantiomeric excesses.     

An efficient synthesis of 5-substituted 1H-tetrazoles via B(C6F5)3 catalyzed [3+2] cycloaddition of nitriles and sodium azide

A simple and efficient protocol is developed for the synthesis of 5-substituted 1H-tetrazole derivatives from various nitriles and sodium azide (NaN₃) via [3+2] cycloaddition reaction using B(C₆F₅)₃ as a catalyst. The present synthetic method displayed significant advantages such as low catalyst loading, mild reaction conditions, low toxicity, easy work-up, high yields, and compatibility with other functional groups.     

Chemoselective O-tert-butoxycarbonylation of hydroxy compounds using NaLaTiO4 as a heterogeneous and reusable catalyst

A facile, efficient and chemoselective protocol for O-tert-butoxycarbonylation of various hydroxy compounds has been developed using NaLaTiO₄ (layered perovskite) as a novel catalyst. The catalyst showed remarkable activity and reusability affording high yields of the desired products under mild reaction conditions.     

A simple protocol for the preparation of β-enamino ketones catalyzed by NbOPO4 under solvent free conditions

A novel application of the highly stable niobium oxide phosphate (NbOPO₄) as an efficient catalyst for the synthesis of β-enamino ketones under solvent-free conditions is described. This protocol, exhibits attractive yields, short reaction periods, lower loading of catalyst and high chemoselectivity.     

Solvent-free synthesis of β-enamino ketones and esters catalysed by recyclable iron(III) triflate

A novel application of highly stable Fe(OTf)₃ as an efficient catalyst for the synthesis of a variety of β-enamino ketones and esters under solvent-free conditions is described. Notably, this protocol of a “green synthesis”, which produced β-enamino ketones and esters by the reaction of a variety of β-dicarbonyl compounds and primary amines, exhibits attractive properties including high yields, short reaction periods, lower loading of catalyst and chemo- and regio-selectivity. In addition, the catalyst was easily recovered from the reaction system and readily reused with minimal loss of activity.     

Deep eutectic solvent promoted highly efficient synthesis of N,N’-diarylamidines and formamides

A deep eutectic solvent was used as a dual catalyst and reaction medium for the efficient N-formylation of aromatic amines without hazardous organic solvent and catalyst. Treatment of aromatic amines with trimethyl orthoformate and formic acid in deep eutectic solvent at 70 °C gives the corresponding N-formyl derivatives in good to excellent yields. This simple ammonium deep eutectic solvent, easily synthesized from choline chloride and SnCl₂, with 100% atom economy and making it applicable to industry and laboratory. Furthermore, heating the trimethyl orthoformate and aromatic primary amines in the deep eutectic solvent results in formation of the corresponding N,N’-diarylamidines in high yields.     

Synthesis of N-aryl trifluoromethylarylketoimines by palladium-catalyzed Suzuki coupling reaction of N-aryltrifluoroacetimidoyl chlorides with aryl boronic acids

A highly efficient Suzuki reaction between N-aryltrifluoroacetimidoyl chlorides and aryl boronic acids using Pd(PPh₃)₄ as a catalyst has been developed. This route allows for selective synthesis of N-aryl trifluoromethylarylketoimines in high yields under mild reaction conditions.     

P(i-PrNCH2CH2)3N: An efficient nonionic catalyst for the regioselective Michael addition of a β,γ-unsaturated ester and a nitrile

Michael additions of a β,γ-unsaturated ester and a nitrile to a variety of α,β-unsaturated ketones can be effected with high regioselectivity and in good yields using P(i-PrNCH₂CH₂)₃N as a catalyst.     

Synthesis of 5-(perfluoroalkylmethyl)-1,3-dioxolan-4-ones

Acid catalysed condensation of F-alkyl α-hydroxy acids with simple aldehydes or ketones gave F-alkyl 1,3-dioxolan-4-ones. When BF₃,OEt₂ was used as the catalyst, the condensation products were obtained in moderate to good yields and the “cis” isomers are largely favoured, while with HOTs/H₂SO₄ as catalyst, poor yields and lower stereoselectivities were observed.     

Enantioselective syntheses of (E)-γ,δ-disubstituted homoallylic alcohols via BF3·OEt2-catalyzed aldehyde allylboration and analysis of the origin of E-selectivity: A1,2 allylic strain vs. syn-pentane interaction

Enantioselective allylboration of aldehydes with α-substituted β-methyl allylboronate was reported. By using BF₃·OEt₂ as the catalyst, γ,δ-disubstituted homoallylic alcohols were obtained in good yields with high E-selectivities and enantioselectivities. Transition state analysis revealed that the disfavored transition state suffers from a syn-pentane interaction between the BF₃ catalyst and axially oriented α-substituent of the allylboron reagent. Such a syn-pentane interaction is severe enough to overcome the A^1,2 allylic strain between the β-methyl group and the α-substituent of the boron reagent that is present in the favored competing transition state. Consequently, the reaction proceeded with equatorial placement of the α-substituent to furnish γ-methyl substituted homoallylic alcohols with high E-selectivity.     

A simple, efficient and highly selective deprotection of t-butyldimethylsilyl (TBDMS) ethers using silica supported sodium hydrogen sulfate as a heterogeneous catalyst

t-Butyldimethylsilyl (TBDMS) ethers have been efficiently and selectively deprotected using silica supported sodium hydrogen sulfate (NaHSO₄·SiO₂) as a heterogeneous catalyst at room temperature to regenerate the parent alcohols in high yields.     

Symmetric diarylacetylenes: one-pot syntheses and solution photoluminescence

Bis(tri-n-butylstannyl)acetylene was synthesized and used to create a series of symmetric diarylacetylenes via a one-step Stille coupling protocol with Pd(PPh₃)₄ as the catalyst. In many cases, the product simply crystallized in good yields from the reaction mixture upon cooling after reflux at 100 °C or upon removal of solvent. The diarylacetylenes were studied using UV-vis and fluorescence spectroscopies, which showed that naphthyl- and biphenyl-substituted acetylenes had very high solution-state fluorescence quantum yields.     

Nano-SiO2 catalyzed three-component preparations of pyrano[2,3-d]pyrimidines, 4H-chromenes,and dihydropyrano[3,2-c]chromenes

An efficient one-pot three-component procedure has been developed for the preparation of tetrahydrobenzo[b]pyrans, dihydropyrano[3,2-c]chromenes, and pyrano[2,3-d]pyrimidines using nano-SiO₂ as catalyst in H₂O at 70 °C. This methodology has a number of advantages such as: use of reusable catalyst, easy access, short reaction times, high yields, easy work up and use of non-toxic and green solvent.     

Hafinium (IV) promoted synthesis of 2,3-unsaturated N- and C-pseudoglycosides via Type I Ferrier Rearrangement

By using Hf(OTf)₄ as the catalyst, a series of 2,3-N- and C-unsaturated-glucosides have been synthesized from 3,4,6-tri-O-acetyl-d-glucal, 2,4,6-tri-O-benzyl-d-glucal and ((2R,3S)-3-acetoxy-2,3-dihydrofuran-2-yl)methyl acetate under mild reaction conditions in good yields with high anomeric selectivities.     

Copper-catalyzed one-pot N-alkenylation and N-alkylation of amides: an efficient synthesis of substituted 2,3-dihydropyrroles

A novel copper-catalyzed synthesis of substituted 2,3-dihydropyrroles via one-pot N-alkenylation and N-alkylation of amides with 1,4-diiodobut-1-ene derivatives has been developed. The reactions proceed in good to high yields using CuI as the catalyst, K₂CO₃ as the base, and rac-trans-N,N′-dimethylcyclohexane-1,2-diamine as the ligand.     

Polystyrene-bound electron-deficient tin(IV) porphyrin: A new, highly efficient, robust and reusable catalyst for acetylation of alcohols and phenols with acetic anhydride

In the present work, tetrakis(p-aminophenyl)porphyrinatotin(IV) trifluoromethanesulfonate, [Sn^IV(TNH₂PP)(OTf)₂], supported on chloromethylated polystyrene was prepared and characterized by elemental analysis, FT IR and diffuse reflectance UV-Vis spectroscopic methods. This new heterogenized catalyst was used for acetylation of alcohols and phenols with acetic anhydride in short reaction times and high yields. The catalyst is of high reusability and stability in the acetylation reactions and was recovered several times without loss of its initial activity and catalyst leaching.     

Nano-ferrous ferric oxide (nano-Fe3O4): Powerful,reusable, and stable catalyst for N-Boc protection of amines

Nano-ferrous ferric oxide (nano-Fe₃O₄) efficiently catalyzed N-boc protection of amines in high yields and acceptable reaction times. Nano-Fe₃O₄ was applied as an efficient, green, heterogeneous and reusable magnetite catalyst. Clean reaction, simple purification, short reaction time and high yield were some other advantages of this compound.     

Use of highly reactive, versatile and air-stable palladium-phosphinous acid complex [(t-Bu)2P(OH)]2PdCl2 (POPd) as a catalyst for the optimized Suzuki-Miyaura cross-coupling of less reactive heteroaryl chlorides and arylboronic acids

Using highly reactive air-stable palladium-phosphinous acid complex [(t-Bu)₂P(OH)]₂PdCl₂ (POPd) as a catalyst, synthesis of heteroaryl-aryl cross-coupled products via palladium-catalyzed Suzuki-Miyaura coupling of less reactive substituted 3-chloropyridines with arylboronic acids was achieved in high yields.     

High performance of nitrogen-doped carbon-supported cobalt catalyst for the mild and selective synthesis of primary amines

A nitrogen-doped carbon-supported Co catalyst (Co/N-C-800) was discovered to be highly active for the reductive amination of carbonyl compounds with NH₃ and the hydrogenation of nitriles into primary amines using H₂ as the hydrogen source. Structurally diverse carbonyl compounds were selectively transformed into primary amines with good to excellent yields (82.8–99.6%) under mild conditions. The Co/N-C-800 catalyst showed comparable or better catalytic performance than the reported noble metal catalysts. The Co/N-C-800 catalyst also showed high activity for the hydrogenation of nitriles, affording the corresponding primary amines with high yields (81.7–99.0%). An overall reaction mechanism is proposed for the reductive amination of benzaldehyde and the hydrogenation of benzonitrile, which involves the same intermediates of phenylmethanimine and N-benzylidenebenzylamine.