Heterogeneous gold(I)-catalyzed [2 + 2 + 2] annulation between ynamides and nitriles: Straightforward synthesis of tetrasubstituted pyrimidines

A novel and highly efficient heterogeneous gold(I)-catalyzed [2 + 2 + 2] annulation between ynamides and nitriles has been developed that proceeds smoothly under mild conditions and provides a general and powerful tool for the preparation of a variety of tetrasubstituted pyrimidines with high atom-economy, good to excellent yield, and recyclability of the gold(I) catalyst. The reaction is the first example of the heterogeneous gold(I)-catalyzed construction of pyrimidines.     

N-Heterocyclic carbene-catalyzed [4 + 2] cyclization of α-chloroaldehydes and aurones: Highly enantioselective synthesis of benzofuran-fused dihydropyran-2-ones

The chiral N-heterocyclic carbene-catalyzed [4 + 2] annulation of α-chloroaldehydes and aurones was developed, giving the corresponding benzofuran–fused dihydropyranones in good to high yields with good cis-selectivities and excellent enantioselectivities. The catalytic cycle features with the generation of enolate from chloroaldehdye and its following [4 + 2] cycloaddtion with aurones.     

Metal-free approach for the ʟ-proline mediated synthesis of nitrones from nitrosobenzene

An efficient, and metal-free approach for the ?-proline mediated synthesis of nitrones from nitrosobenzene and benzaldehydes has been established. The reaction undergoes very efficiently at room temperature in methanol as a solvent. The reaction is assumed to involve that the initial formation of azomethine ylide and [2 + 3] cycloaddition of nitrosobenzene, followed by the subsequent retro [2 + 3] cycloaddition could offer the desired nitrone.     

Double [3 + 2] cycloaddition of nitrile oxides with allenoates: Synthesis of spirobidihydroisoxazoles

The double [3+2] cycloaddition of allenoates with nitrile oxides was presented. The reaction worked well under mild reaction conditions to give the spirobidihydroisoxazole in moderate to excellent yields with excellent diastereoselectivities.     

Metal-free visible-light-promoted intermolecular [2+2]-cycloaddition of 3-ylideneoxindoles

The Rose Bengal sensitized intermolecular [2 + 2]-cycloaddition of 3-ylideneoxindoles for the synthesis of spirocyclic oxindoles was developed successfully under visible light irradiation conditions. The cycloaddition products were obtained in good yields (up to 93%) with excellent diastereoselectivity and regioselectivity by using a low loading of Rose Bengal (0.125 mol%) as a triplet sensitizer. This work demonstrates the potential benefits of Rose Bengal in visible light catalysis.     

Triethylamin-mediated addition of 2-aminoethanethiol hydrochloride to chalcones: Synthesis of 3-(2-aminoethylthio)-1-(aryl)-3-(thiophen-2-yl) propan-1-ones and 5,7-diaryl-2,3,6, 7-tetrahydro-1,4-thiazepines

The triethylamin-mediated addition of 2-aminoethanethiol hydrochloride to chalcone analogs was investigated. This addition, bearing a 2-thienyl group at the 3-position, gave the only addition adduct at room temperature in 3 h, whereas the chalcones bearing the 2-furyl group at the 1-position gave an addition-cyclization product (1, 4-thiazepine) in the same conditions. The effect of the groups to the reaction was investigated by changing the 1- and 3-position groups. The chalcones bearing the 2-thienyl group at the 1-position and the others afforded the mixture of products in different ratio at rt for 0.5–24 h. Moreover, the addition–cyclization products (1,4-thiazepine) were obtained under reflux conditions in 36 h. The structures of the synthesized compounds were elucidated by ¹H NMR, ¹³C NMR, infrared, and elemental analysis.     

Synthesis of Chlorin-Fused Monospirooxindolopyrrolidines Through a Facile [3 + 2]-Cycloaddition of Azomethine Ylides

One-pot synthesis of novel chlorin-fused monospirooxindolopyrrolidines has been accomplished in good yield via a facile [3 + 2]-cycloaddition reaction of azomethine ylides, derived from isatin/N-benzylisatin and sarcosine, with various porphyrin derivatives as dipolarophiles.     

Cyclocondensation of chalcones with 2-amino- and 1,2-diaminobenzimidazoles

2,4-Diaryl-1,4-dihydropyrimido[1,2-a]benzimidazoles were obtained by the reaction of 2-aminobenzimidazole with chalcones, and their heteroaromatization was accomplished. The condensation of 1,2-diaminobenzimidazole with unsymmetrically substituted chalcones, which leads to substituted pyrimido-[1,2-a]benzimidazoles, was studied. The specificity of this reaction was ascertained by means of alternative synthesis.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1071–1075, August, 1989.     

One-pot synthesis of oxygen and nitrogen-bridged calix[2]arene[2]triazines

A simple and powerful one-pot reaction method was developed for the synthesis of heteracalixaromatics. In the presence of a base, one-pot macrocyclic condensation reaction between cyanuric chloride and 1,3-phenylene diols and diamines proceeded effectively under very mild conditions to afford a number of functionalised oxygen and nitrogen-bridged calix[2]arene[2]triazines in 33–54% yields. The method was applied in a multigram-scale (14.4 g) preparation of tetraoxacalix[2]arene[2]triazine.     

An efficient RuCl3·H2O/I2 catalytic system: A facile access to 3-aroylimidazo[1,2-a]pyridines from 2-aminopyridines and chalcones

A simple and efficient protocol has been demonstrated for the preparation of densely functionalized 3-aroylimidazo[1,2-a]pyridines from 2-aminopyridines and chalcones using RuCl₃·H₂O/I₂ catalytic system. The advantages, such as low catalyst loading, broad substrate scope with respect to substitutions on aminopyridines as well as chalcones, stability of heterocycles such as thiophene under the reaction conditions, operationally simple procedure and higher yields makes this approach remarkable for synthetic applications.     

An unusual [4 + 4] cycloadduct from an o-quinodimethane: Characterisation and computational studies

Trapping of a pyrimidinone-derived o-quinodimethane with tetraphenylcyclopentadienone gives a mixture of the [4 + 2] and formal [4 + 4] adducts. Computational studies show that the latter arises by a sequence of [4 + 2] cycloaddition, homolysis, radical recombination to a spiro-tetrahydrofuran and Claisen rearrangement under the thermolytic conditions.     

Synthesis of New 2-[(Substituted-pyrazolin-1-yl)carbonyl]-thieno[2,3-b]pyridine Derivatives

The reaction of 3-amino-4,6-dimethyl-2-thieno[2,3-b]pyridine carbohydrazide ( 1 ) with appropriate chalcones 2a-2d in the presence of acid catalyst produced the corresponding 3-amino-2-[(3,5-disubstituted-pyrazolin-1-yl)carbonyl]-4,6-dimethylthieno[2,3-b]pyridines 3a-3d . 3-Amino-2-[(3-substituted-pyrazolin-1-yl)carbonyl]-4,6-dimethylthieno[2,3-b]pyridines 7a, 7b were also obtained by the cyclization reaction of carbohydrazide 1 with Mannich base derivatives 6a, 6b under basic condition.     

Concise synthesis of the core structure of madreporanone by Rh-catalyzed [3+2] cycloaddition

A model study toward total synthesis of madreporanone, a novel diterpene isolated from Azorella madreporica, was investigated. The [3.3.0] bicyclic core of madreporanone bearing a cis-configured isopropyl group and two vicinal quaternary carbon centers was stereoselectively constructed via an intramolecular Rh-catalyzed [3 + 2] cycloaddition in a single step.     

Temperature-Gradient-Directed NMR Monitoring of a [3 + 3]-Cyclocondensation Reaction Between Alkynone and Ethyl 2-Amino-1H-indole-3-carboxylate Toward the Synthesis of Pyrimido[1,2-a]indole Catalyzed by Cs2CO3

We describe a NMR strategy to resolve temperature-gradient-monitored real-time chemical reaction involving a [3 + 3]-cyclocondensation reaction between alkynone and ethyl 2-amino-1H-indole-3-carboxylate toward the synthesis of pyrimido[1,2-a]indole catalyzed by Cs₂CO₃. The in situ NMR study clearly indicates that the reactant undergoes [3 + 3]-cyclocondensation reaction through a concerted mechanism, resulting in the product formation. The detailed NMR spectroscopic data led to the optimization of the reaction conditions and quantitative analysis of the product accurately and efficiently.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.     

Synthesis of Novel Spiro[indol-2,2′-pyrroles] Using Isocyanide-Based Multicomponent Reaction

An efficient and facile method for the synthesis of novel spiro[indole-2,2′-pyrroles] from N-methyl-3-isatin imines, t-butyl isocyanide, and dialkyl acetylenedicarboxylate has been achieved by [3 + 2] cyclo addition reaction. All the products were purified by column chromatography as yellow solids and confirmed with ¹H NMR, ¹³C NMR, fast atom bombardment, mass, and infrared. Compound 11 was further confirmed with x-ray analysis.     

Microwave Synthesis of 5-Substituted 1H-Tetrazoles Catalyzed by Bismuth Chloride in Water

Bismuth chloride was used to catalyze the [2 + 3] cycloaddition between sodium azide with aryl nitriles, aliphatic nitriles, and vinyl nitriles. A number of 5-substituted 1H-tetrazoles were synthesized in water or isopropanol/water mixtures using microwave heating. Good yields were obtained for these reactions when heated for 1 h at 120–160 °C in a 3:1 isopropanol/water mixture. A few of the less reactive nitriles required longer reaction times for good yields.     

An efficient route to quinoline-2-carboxylates via a rhodium-catalyzed oxidative [5+1] annulation of 2-vinylanilines with α-diazocarbonyl compounds

A novel rhodium-catalyzed oxidative [5 + 1] annulation of 2-vinylanilines with α-diazocarbonyl compounds for the construction of quinoline-2-carboxylate derivatives has been developed. A series of functional groups such as methyl, methoxy, fluoro, chloro, bromo, cyano, and even thienyl substituents were tolerated well. This methodology has the potential for use in the pharmaceutical industry.     

Understanding the domino reactions of alkyne-tethered N-tosylhydrazones yielding fused polycyclic pyrazoles. An MEDT study

The domino reactions of alkyne-tethered N-mesylhydrazones yielding fused polycyclic pyrazoles have been studied within the Molecular Electron Density Theory (MEDT). Analysis of the Gibbs free energies indicates that the more favourable reactive path is the one in which the elimination of mesylate anion takes place before the intramolecular [3 + 2] cycloaddition (IM32CA) reaction, which corresponds with the rate-determining step of these domino processes. ELF topological analysis of the bond formation along the IM32CA reaction indicates that in spite of the high activation energy associated to this intramolecular reaction, it shows a pmr-type mechanism characterised by the presence of a pseudoradical carbon at the phenyldiazomethane framework.     

Viscosity reduction of cellulose + 1-butyl-3-methylimidazolium acetate in the presence of CO2

Viscosities of microcrystalline cellulose + 1-butyl-3-methylimidazolium acetate ([bmIm][Ac]) solutions (0.6–1.2 wt%) in contact with CO₂ were measured at 312 K with a resonant vibrational viscometer. At 4 MPa and 312 K, the CO₂ could reduce the viscosity of 1.2 wt% cellulose + [bmIm][Ac] solution by about 80 %, whereas N₂ at the same conditions gave less than a 10 % reduction in viscosity. The viscosity-averaged degree of polymerization and IR spectrum showed that cellulose did not decompose during experiments and that [bmIm][Ac] acted as a non-derivatizing solvent during the dissolution and viscosity reduction process. Further, although CO₂ does react with [bmIm][Ac] to form 1-butyl-3-methylimidazolium-2-carboxylate, the reaction seems to be reversible and it does not affect the cellulose. Thus, [bmIm][Ac] with CO₂ provides an effective solvent for cellulose and the solvent system can probably be recycled or reused.     

A Clean and Expedient Synthesis of Pyrido[1,4]oxazepino Spiropyrrolidines Through One-Pot,Three-Component [3 + 2] Cycloaddition Reaction

One-pot three component synthesis of novel pyrido[1,4]-oxazepine fused spiropyrrolidines has been accomplished in good yields by 1,3-dipolar cycloaddition reaction of azomethine ylide, derived from paraformaldehyde and sarcosine with (E)-4-benzylidene-hexahydro-1H-pyrido[2,1-c][1,4]-oxazepine-3(7H)-one as dipolarophiles derived from Baylis-Hillman adducts. The effect of solvent on the [3 + 2]-cycloaddition reaction is also studied.