Heterocyclic o-Chloroaldehydes as Synthons in Organic and Inorganic Sulfur Chemistry

Abstract

Many heterocyclic o-chloroaldehydes are easy to prepare, for example via the Vilsmeier chloroformylation reaction. Due to the electron withdrawing effect of the formyl group, the halogen atom is normally a nucleofuge. This can be used to prepare a range of o-substituted heterocyclic aldehydes showing interesting rearrangement reactions. Such types of compounds are also useful as starting materials for the preparation of annelated heterocyclic systems.

We have demonstrated that heterocyclic mercapto groups can be protected as t-butylthioethers. Furthermore, we have found that thiolation of heterocyclic systems containing reactive halogen substituents can conveniently be carried out via the easily prepared t-butylsulfides.

This method has been used in the preparation of a number of N₂S₂-ligands. The resulting transition metal N₂S₂-complexes have been used in the study of model systems for one of the active sites in cytochrome c oxidase. The method also gives access to polymeric heterocyclic multisulfur transition metal complexes with high electrical conductivity.     

Cyclic Amino(Ylide) Silylene: A Stable Heterocyclic Silylene with Strongly Electron‐Donating Character

An isolable heterocyclic silylene ( 4 ) with two different π‐donating substituents, namely a classical amino group and a more electropositive and stronger carbon‐based π‐donating phosphonium ylide, was synthesized and fully characterized. The combination of these two different π‐donating substituents confers high thermal stability and an unusual nucleophilic character on silylene 4 . Therefore, silylene 4 behaves as a strong donor ligand toward transition metals with a donating character comparable to N‐heterocyclic carbenes, in contrast to classical N‐heterocyclic silylenes, which generally present a weak donating character.     

Spectroscopic study of rigid-rod polymers. II. Protonation effect

The protonation of a heterocyclic rigid-rod polymer poly(p-phenylene benzbisthiazole) and its model compound has been studied by UV-visible and Raman spectroscopy. Because of the two nitrogens on the heterocyclic ring, spectroscopic features of unprotonated, half-protonated, and fully protonated structures have been identified. For the fully protonated molecule, there is also an increase in conjugation between the phenyl ring and the heterocyclic ring.     

Exceptionally Strong Electron‐Donating Ability of Bora‐Ylide Substituent vis‐à‐vis Silylene and Silylium Ion

Electropositive boron‐based substituent (phosphonium bora‐ylide) with an exceptionally strong π‐ and σ‐electron donating character dramatically increases the stability of a new type of N ‐heterocyclic silylene 2 featuring amino‐ and bora‐ylide‐substituents. Moreover, the related silylium ion 4 and transition‐metal–silylene complexes, with trigonal‐planar geometries around the silicon center, are also well stabilized. Therefore, the N,B‐heterocyclic silylene 2 can be used as a strongly electron‐donating innocent ligand in coordination chemistry similarly to N ‐heterocyclic carbenes.     

The synthesis of N-containing heterocyclic compounds catalyzed by copper/L-proline

N-containing heterocyclic compounds are one of the most important motifs prevalent in various bioactive natural products and pharmaceuticals. Given the significance of N-containing heterocyclic compounds, various synthetic strategies have been developed. Copper/ligand (abbreviated as [CuL])-catalyzed cascade reaction is a powerful and efficient tool for the construction of N-containing heterocyclic compounds. L-proline is one universal ligand and has been utilized in the copper-catalyzed reactions. In this review, copper/L-proline-catalyzed tandem reaction to synthesize the five- and six-membered compounds is emphatically introduced. By comparing the yields in the presence and absence of the ligand, the importance of L-proline is recorded. Moreover, the function of L-proline is expounded on the basis of the reaction mechanism from original article.     

Synthesis of 5-amino-1,3-dimethylpyrazol-4-yl aryl ketones

A convenient preparation of 5-amino-1,3-dialkylpyrazol-4-yl heterocyclic ketones is reported. They are prepared from the reaction of heterocyclic esters with the di-lithio derivative from N-(4-bromo-1,3-dimethyl-1H-pyrazol-5-yl)benzamide ( 1 ).     

Heptaphyrins: Expanded porphyrins with seven heterocyclic rings

Expanded porphyrins containing seven pyrrole/heterocyclic rings linked in a cyclic fashion are termed heptaphyrins. The number ofπ-electrons in heptaphyrins depends on the number ofmeso carbon bridges used to link the heterocyclic rings, accordingly heptaphyrins with 28π-electrons and 30π-electrons are reported to date. Both condensation reactions of the appropriate precursors and acid-catalysed oxidative coupling reactions have been utilized to synthesise the heptaphyrins. The 30π heptaphyrins exhibit rich structural diversity where some of the heterocyclic rings in the macrocycle undergo a 180° ring flipping. An overview of the synthetic methods employed for the synthesis of heptaphyrins, their spectroscopic properties, structural behaviour and aromatic properties are highlighted in this paper. Dedicated to Professor C N R Rao on his 70th birthday     

Synthesis of functionalized pyrroles and fused pyrroles through intermolecular [3 + 2] cycloaddition reaction

A facile and efficient synthesis of pyrrole and pyrrole-fused heterocyclic compounds has been demonstrated. The current protocol involves the in situ generation of azomethine ylides which undergoes intermolecular cycloaddition reaction and subsequent treatment with DDQ provides the pyrrole and fused heterocyclic compounds in good yields.     

Domino Reactions of 3‐Vinylchromone Leading to Different Heterocyclic Compounds

A range of heterocyclic systems incorporating chromone and related scaffolds was synthesized via domino reactions of 3‐vinylchromone. These cascade processes resulted in the construction of various heterocyclic nuclei such as xanthone and enaminone as well as diazolo and triazolo chomenopyrimidine heterocycles.     

N‐Heterocyclic Carbene‐Catalyzed α‐Alkylation of Ketones with Primary Alcohols

Several N‐heterocyclic carbene precursors are synthesized and used in the α‐alkylations of ketones with primary alcohols. With the assistance of a base, these N‐heterocyclic carbenes can catalyze the reaction smoothly to furnish dialkylated ketones in good‐to‐excellent yields.     

Synthèse d'hétérocycles en catalyse par transfert de phase

A general study of the chemical behavior of heterocyclic anions, dianions and dianionic reagents under phase transfer catalysis conditions allowed us to synthesize various heterocyclic compounds such as imidazo[2,1-b]thiazole and derivatives; imidazo[2,1-b]thiazine and imidazo[2,1-b]benzothiazepine. Reaction conditions e.g., catalyst, solvent, temperature, etc., are indicated.     

Nucleophilic Reaction of Heterocyclic Enamines with Nitrile imine 1,3-Dipoles

Instead of 1,3-dipolar cycloaddition, the nucleophilic addition reaction proceeded smoothly between heterocyclic enamines 1 or 2 and nitrile imine 1,3-dipoles 3 under mild conditions to yield C-hydrazidoyl-substituted heterocyclic enamines 4--6 as the sole product.     

Heterocycles from amino acids. A novel synthetic approach for imidazo[1,5-a]pyridines and imidazo[1,5-a]quinolines

From the corresponding heterocyclic amino acids 2 and 9a the heterocyclic systems imidazo[1,5-a]pyridine ( 3 ) and imidazo[1,5-a]quinoline ( 10 ) are easily accessible. From compound 7 the tricyclic system 11 was prepared and from compound 17a a pyridyl-1,2,4-triazinone ( 18 ) could be obtained.     

Dimroth rearrangement in the row of new pyrano[3,4-c][1,2,4]triazolo[4,3-a][1,5-a]pyridines and synthesis of new heterocyclic systems: Pyranopyrazolo[4,3-e][1,2,4]triazolopyridines

New and effective methods for the synthesis of derivatives of pyrano[3,4-c][1,2,4]triazolo[4,3-a][1,5-a]pyridines were developed. Synthesized new tetracyclic heterocyclic systems containing pyrano[3,4-c]pyridine ring unknown in the literature were obtained for the first time. The rearrangement of Dimroth in the triazolo[4,3-a]pyridine systems for the first time was studied. The possibility of rearrangement of Dimroth in the new heterocyclic system has been investigated.     

Interaction of N‐Heterocyclic Carbenes and Simple Carbenes with Small Molecules (One to Three Atoms) Excluding Metals: Formation of Covalent C–X Bonds

This review reports the reactivity of carbenes (>C : ), both N‐heterocyclic and simpler ones, with 29 small molecules to form C–X bonds and some weak interactions. The structures thus obtained belong to many functional groups proving the characteristic reactivity of N‐heterocyclic carbenes. Particular attention has been paid to X‐ray structures that are useful for theoretical calculations.     

Synthesis of tetracyclic thienotriazolopyridines based on hydrazine derivatives of fused pyridinethiones

A method for the synthesis of hydrazine derivatives of fused pyridinethiones based on alicyclic and heterocyclic ketones has been developed. Successive heterocyclization of these hydrazine derivatives was carried out in order to obtain new derivatives of tricyclic triazolo[4,3-a]pyridines, tetracyclic thieno[3,2-e][1,2,4]triazolo[4,3-a]pyridines, as well as a new heterocyclic system of thieno[2,3-c][1,2,4]triazolo[3,4-a]-2,7-naphthyridine.

     

Asymmetric Synthesis of Chiral Trifluoromethyl Containing Heterocyclic Amino Acids

An operationally convenient, asymmetric synthesis of chiral trifluoromethyl containing heterocyclic amino acids has been developed via Michael addition reaction of chiral equivalent of Ni(II)‐complex of glycine and β ‐trifluoromethylated‐α ,β ‐unsaturated ketones. The simplicity of the experimental procedures and high stereochemical outcome of the presented method render these heterocyclic amino acids readily available for systematic medicinal chemistry studies and de novo peptide design.     

Synthesis of 7,8‐Dihydrothieno[3′,2′:4,5]pyrrolo[1,2‐a]pyrazin‐5(6H)‐ones Using a Modification of Four‐Component Ugi Reaction

We describe an efficient synthesis of novel 7,8‐dihydrothieno [3′,2′:4,5]pyrrolo[1,2‐a]pyrazin‐5(6H)‐one heterocyclic structures. The target compounds were prepared by a novel modification of four‐component Ugi reaction of heterocyclic bifunctional keto acids, isonitriles, and amines. We demonstrate the usefulness and versatility of the developed approach, which is amenable to production of combinatorial libraries.     

Nonaqueous diazotization of 4-amino-3-arylisothiazole-5-carboxylate esters

4-Amino-3-arylisothiazole-5-carboxylate esters are converted to the corresponding desamino, chloro, bromo, and iodo esters by processes involving nonaqueous diazotization. These related procedures open up the possibility for the conversion of readily available heterocyclic ortho-amino esters and nitriles to related heterocyclic derivatives, which are not easily obtained by alternate routes.     

Well-defined (NHC)Pd(N–heterocyclic carboxylate)(OAc) complexes-catalyzed direct C2-arylation of free (NH)-indoles with arylsulfonyl hydrazides

A series of well-defined (NHC)Pd(N–heterocyclic carboxylate)(OAc) complexes (N–heterocyclic carboxylate = pyridine-2-carboxylate, quinoline-2-carboxylate and isoquinoline-1-carboxylate) were synthesized and fully characterized by NMR spectra, HR-MS and X-ray single crystal diffraction. The obtained complexes were then used for direct C2-arylation of free (NH)-indoles with arylsulfonyl hydrazides. With low catalyst loading, all complexes exhibited high catalytic activities for the arylation reactions.