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.     

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.     

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.     

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.     

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 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.

     

Copper‐Catalyzed Enantioselective Markovnikov Protoboration of α‐Olefins Enabled by a Buttressed N‐Heterocyclic Carbene Ligand

Reported is a highly enantioselective copper‐catalyzed Markovnikov protoboration of unactivated terminal alkenes. A variety of simple and abundant feedstock α‐olefins bearing a diverse array of functional groups and heterocyclic substituents can be used as substrates, and the reaction proceeds under mild reaction conditions at ambient temperature to provide expedient access to enantioenriched alkylboronic esters in good regioselectivity and with excellent enantiocontrol. Critical to the success of the protocol was the development and application of a novel, sterically hindered N‐heterocyclic carbene, (R,R,R,R)‐ANIPE, as the ligand for copper.     

Mutagenic heterocyclic nitrogen compounds related to protein pyrolysates. 1. Derivatives of dipyrido[1,2-a:3′,2′-d]imidazole

2-Amino-6-methyldipyrido[1,2-a:3′-2′-d]imidazole is one of the mutagenic principles of L-glutamic acid and casein pyrolysates. We prepared several isomeric amines of this compound, as well as their homologues methylated in different positions on the heterocyclic ring, either by nitration of the ring followed by reduction or from appropriate 4-azidodipyrido[1,2-a:3′,2′-d]imidazoles. The latter compounds, the heterocyclic ring itself and various functional derivatives (hydroxylated, carboxylated, hydrazinic) were synthesized from 2-aminoimidazo[1,2-a]pyridines via various reactions which are described herein.     

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 ).     

Formation of N‐Heterocyclic Carbenes by Tautomerization of Mesomeric Betaines: Cyclic Boron Adducts and Palladium Complexes From 2‐(Imidazolium‐1‐yl)phenolates

2‐(Imidazolium‐1‐yl)phenolates are conjugated heterocyclic mesomeric betaines in tautomeric equilibrium with the corresponding N‐heterocyclic carbenes (NHCs), 3‐(2‐hydroxyphenyl)‐imidazol‐2‐ylidenes. The carbene tautomers can be trapped as thiones (X‐ray analysis). Moreover, bis(triphenylphosphine)palladium(II) dichloride in THF trapped the carbene tautomer as a palladium complex without participation of the phenolate group (X‐ray analysis). The corresponding anionic NHCs, 2‐phenolate‐substituted imidazol‐2‐ylidenes, can be trapped by triethylborane or triphenylborane to form 4,4‐diethyl‐ or 4,4‐diphenyl‐4H‐benzo[e]imidazo[2,1‐c][1,4,2]oxaza‐borininium‐4‐ides, respectively (two X‐ray analyses). These tricyclic systems are the first representatives of a new heterocyclic ring system. The results of DFT calculations concerning the HOMO/LUMO profiles and partial charges are also presented.     

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.     

Palladium acetate assisted synthesis of five-membered N-polyheterocycles

Abstract

The metal-assisted synthesis of heterocyclic compounds is known to be one of the extremely developing as well as significant concepts of organic chemistry. Because of their expensive, complex working of the instrument and difficult procedures, the methodologies used earlier for the heterocycle synthesis were less amicable to the researchers. The Pd(OAc)₂-mediated cyclic reactions have been recognized to be very effective for both the stereoselective as well as regioselective formation of the 5-membered N-bearing heterocyclic compounds. The different uses of palladium acetate, as a catalyst in the formation of 5-membered N-containing polyheterocycles, are covered in this review article.     

Dithiadiazolyls as heterocyclic chelators: a radical approach to coordination chemistry?

The ability of heterocyclic compounds to act as chelating ligands via the cleavage of a heterocyclic E–E (or E–E′) bond with concomitant formation of M–E (and M–E′) bonds is described with particular reference to the 7π heterocyclic dithiadiazolyl radicals, R

. These electron-rich ring systems form a diversity of structural bonding types in which the heterocyclic ring can formally act as a 2e⁻, 3e⁻, 5e⁻ or 6e⁻ donor ligand. These structural bonding modes are described through examples in which the heterocyclic ring interacts with halide anions, N atoms and particularly metal centres, forming monometallic, dimetallic and trimetallic complexes. The structural features which determine which compounds are likely to act as cyclic chelators are discussed and examples of thiadiazole, diselenadiazolyl and dithiole rings acting as cyclic chelators are given.     

Generating and Trapping Metalla‐N‐Heterocyclic Carbenes

By means of a combined experimental and theoretical approach, the electronic features and chemical behavior of metalla‐N‐heterocyclic carbenes (MNHCs, N‐heterocyclic carbenes containing a metal atom within the heterocyclic skeleton) have been established and compared with those of classical NHCs. MNHCs are strongly basic (proton affinity and pK_a values around 290 kcal mol^?1 and 36, respectively) with a narrow singlet–triplet gap (around 23 kcal mol^?1). MNHCs can be generated from the corresponding metalla‐imidazolium salts and trapped by addition of transition‐metal complexes affording the corresponding heterodimetallic dicarbene derivatives, which can serve as carbene transfer agents.     

Benzoylhydrazones in catalytic hydrophosphorylation

Reactions of benzoylhydrazones derived from heterocyclic and aromatic aldehydes and aliphatic, heterocyclic, and aliphatic-aromatic ketones with diethyl phosphite in the presence of [tetra(tert-butyl)phthalocyanine]aluminum chloride afford α-benzoylhydrazino phosphonates in high yields.     

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.     

Preparation of novel axially chiral NHC–Pd(II) complexes and their application in oxidative kinetic resolution of secondary alcohols

Novel axially chiral N‐heterocyclic carbene (NHC) Pd(II) complexes were prepared from optically active 1,1′‐binaphthalenyl‐2,2′‐diamine (BINAM) and H₈‐BINAM and their crystal structures were unambiguously determined by X‐ray diffraction. These chiral N‐heterocyclic carbene (NHC) Pd(II) complexes were applied in the oxidative kinetic resolution of secondary alcohols using molecular oxygen as a terminal oxidant or under aerobic conditions, affording the corresponding sec‐alcohols in good yields with moderate to good enantioselectivities. Copyright © 2009 John Wiley & Sons, Ltd.     

Studies on the Adamantylation of N-Heterocycles and Nucleosides

Adamantylation of several N-heterocycles and of two ribonucleosides (uridine and toyocamycin) was studied. The exact substitution position by the adamantyl carbocation generated from adamantan-1-ol in CF₃COOH depends on the nature of the heterocyclic substrate. Thus, adamantylation of an additional exocyclic amino group (see Scheme 1), N-adamantylation of the heterocycle (Scheme 2), C-adamantylation of the heterocycle (Scheme 3), as well as the formation of heterocyclic N-adamantylcarboxamides via the Ritter reaction (Scheme 4) are possible. The structures of the reaction products were determined by means of elemental analysis and NMR, UV, and IR spectroscopy.     

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.