First functionalization by metallation of the pyridine moiety of 4-methoxypyridopyrimidines. Diazines: Part 38

Starting from pyridopyrimidin-4(3H)-ones, a general synthetic route leading to 4-methoxypyridopyrimidines is described. The first lithiation and functionalization of the pyridine moiety has been studied. According to various structural parameters, the regioselectivity of the metallation is discussed. The functionalization of the 4-methoxypyridopyrimidines via the metallation reaction, provides an efficient process to access new substituted pyridopyrimidines.     

Pyridino-directed lithiation of anisylpyridines: new access to functional pyridylphenols

The lithiation of nine anisylpyridines has been studied. While usual reagents did not react or gave addition products on pyridine ring, the BuLi-LiDMAE (LiDMAE=Me₂N(CH₂)₂OLi) superbase induced exclusive pyridino directed metallation. The usefulness of this new reaction allowed the efficient preparation of a range of alpha functional pyridylphenols. A successful subsequent cyclisation of an appropriate isomer into corresponding benzofuropyridine was also performed.     

A pyridine promoted ‘weak base route’ to (NHC)2NiCl2 complexes with bulky N,N'-diaryl carbene ligands

A simple one-step synthesis of (NHC)₂NiCl₂ complexes containing bulky N-heterocyclic carbene (NHC) ligands relies on the C–H metallation of N,N'-diaryl-substituted azolium salts, NHC-precursors, with NiCl₂Py₂ in the presence of Cs₂CO₃ and pyridine. This procedure allows one to implement all synthetic manipulations in air.     

Reaction de la bromo-3 pyridine avec le diisopropylamidure de lithium. Mecanismes de metallation et de migration d'halogene. Regioselectivite de l'addition polaire sur la pyridyne-3,4

3-bromo pyridine behaviour towards lithium diisopropyl amide (LDA) in THF is studied. A careful study of the experimental conditions point to a metallation reaction in position 4 and a “halogen dance” mechanism with isomerisation into a 4-bromo pyridine. Conversion into diisopropylamino compounds occurs simultaneously with a 3 oriented elimination-addition (EA) reaction from transient isomeric lithio-derivatives and a competing addition-elimination (AE) mechanism from the in situ formed 4-bromo pyridine.     

Synthesis,characterization and X-ray structures of N-heterocyclic carbene palladium complexes based on calix[4]arenes: highly efficient catalysts towards Suzuki–Miyaura cross-coupling reactions

A new series of calix[4]arene supported N-heterocyclic carbene palladium complexes were developed and fully characterized. A mono-substituted calix[4]arene was prepared through conventional procedures, following with the attachment of imidazolyl derivative groups to compose the precursors of novel NHCs ligands. Undergoing the alkylation with n-butylbromide and corresponding metallation with palladium and pyridine, original complexes were obtained. After a full characterization in solution and solid state, the evaluation of catalytic activity was taken out in Suzuki–Miyaura cross-coupling reactions, which revealed good performances.     

Toward a general method for CCC N-heterocyclic carbene pincer synthesis: Metallation and transmetallation strategies for concurrent activation of three C-H bonds

A general solution to the preparation of pincer complexes that require the formation of two N-heterocyclic carbenes (NHC’s) and the activation of an aryl C-H bond is reported. The reaction of a phenylene-bridged bis(imidazolium) salt with Zr(NMe₂)₄ generated the requisite CCC-NHC Zr pincer complex, which has been characterized by X-ray crystallography. Subsequent manipulation of the Zr coordination sphere by reaction with MeI demonstrated the robustness of the ligand geometry at Zr and led to the isolation and structural characterization of a CCC-NHC Zr triiodide pincer complex. A variation of the methodology has been applied to a saturated NHC analog to produce the corresponding CCC-NHC Zr pincer complex. Importantly, it has been found that CCC-NHC Zr pincer complexes can be generated in situ and transmetallated with an appropriate Rh source to generate CCC-NHC Rh pincer structures. These two methodologies, metallation of CCC-NHC precursors with transition metal amido complexes combined with transmetallation, hold great promise for opening general synthetic pathways to a wide variety of transition metal CCC-NHC pincer complexes.     

One-pot three-component synthesis of functionalized spirolactones by means of reaction between aromatic ketones, dimethyl acetylenedicarboxylate, and N-heterocycles

A simple and convenient one-pot multi-component reaction has been described for the synthesis of functionalized spirolactones. This strategy demonstrated three-component reaction between aromatic ketones (11H-indeno[1,2-b]quinoxalin-11-one) and dimethyl acetylenedicarboxylate (DMAD) in the presence of N-heterocycles, such as pyridine, quinoline, and isoquinoline in CH₂Cl₂ at ambient temperature without use of any catalyst or activator.     

Synthesis and characterization of a tetraruthenium butterfly cluster containing a quadruply-bridging ligand derived from an N,N′-dipyrid-2-ylurea

The tetraruthenium cluster complex [Ru₄(μ₄-κ⁴-dmpu)(CO)₁₀], H₂dmpu = N,N′-bis(6-methylpyrid-2-yl)urea, has been prepared by treating [Ru₃(CO)₁₂] with H₂dmpu in toluene at reflux temperature. An X-ray diffraction study has determined that this cluster has a butterfly metallic skeleton hold up by a doubly-deprotonated N,N′-bis(6-methylpyrid-2-yl)urea ligand (dmpu). This ligand has the pyridine N atoms attached to the wing-tip Ru atoms and the amido N atoms spanning Ru-Ru wing-edges, in such a way that the cluster has C₂ symmetry. The donor atoms of doubly-deprotonated N,N′-dipyrid-2-ylureas seem to be appropriately arranged to hold butterfly tetranuclear clusters.     

A novel reagent combination for the oxidation of highly electron deficient pyridines to N-oxides: trifluoromethanesulfonic anhydride/sodium percarbonate

A novel reagent combination, Tf₂O/Na₂CO₃·1.5H₂O₂, has been developed for the oxidation of highly electron deficient pyridines to their corresponding N-oxides. The N-oxidation reaction, utilizing the in situ generated peracid, proceeds under mild conditions that allow for a number of functional groups and substitution patterns on the pyridine ring.     

Application of ortho-chloro-β-aroylthioamides in synthesis(II): an efficient one-pot, three-component synthesis of tricyclic thiochromeno[2,3-b]pyridine derivatives

Tricyclic thiochromeno[2,3-b]pyridine derivatives have been successfully synthesized in an unusual one-pot multicomponent cascade reaction from ortho-halo-β-aroylthioamides, Meldrum's acid, and aromatic aldehydes. The reaction presumably proceeds via Knoevenagel condensation-Michael addition-cyclocondensation-decarboxylation-rearrangement-intramolecular S_NAr reaction sequence. High bond forming efficiency of this reaction makes it attractive for the synthesis of thiochromeno[2,3-b]pyridine derivatives in a single step operation.     

Synthesis and conformations of chromium tricarbonyl substituted diarenes

The metallation of a series of seven planar and bent diarenes has been examined to determine the conformations of the mono- and dimetallated products. It has been found that bent diarenes can be metallated on either the convex (syn) or concave (anti) faces of the arene. In the absence of other directing groups, metallation at the concave face is favored. Dimetallation of planar diarenes results in exclusive trans metallation. Dimetallation of bent diarenes yields the trans isomer as the major species, but cis dimetallation of the convex face is also observed. Conformational assignments have been made using ¹H and ¹³C NMR spectral evidence.     

Reversible fluorous phase-switching of pyridyl-tagged porphyrins: Application to the sensing of histamine in water

Upon stirring a chloroform/perfluorodecalin biphasic system, the 5,10,15,20-tetrapyridyl porphyrin (TPyP) solubilized in the organic phase was almost quantitatively extracted (∼99.9%) into the fluorous phase containing an excess of the “heavy fluorous” copper(II)-carboxylate complex 1. The porphyrin was quantitatively and almost instantaneously released into the chloroform after addition of excess tetrahydrofuran (THF), which successfully competed with the pyridine ligand for binding sites on complex 1. Metallation of TPyP by copper(II) ions was never observed during the “catch-and-release” process. With the 5,10,15-tripyridyl-20-phenylporphyrin (TPyMPP) or the 5,15-dipyridyl-10,20-diphenylporphyrin (trans-DPyDPP) both efficient extraction (98%) and metallation occurred simultaneously leading to the immobilization of the metallated copper(II)-porphyrins in the fluorous phase. The metalloporphyrins were quantitatively released in the organic phase by addition of THF. With the 5-pyridyl-10,15,20-triphenylporphyrin (MPyTPP) no extraction but rapid metallation was observed under biphasic stirring leading to the quantitative recovery of the Cu²⁺-metalloporphyrin in the organic phase. The “catch-and-release” methodology of TpyP was exploited to develop a triphasic C₆F₁₄/DCM/water indicator displacement assay (IDA) for histamine in which the receptor–indicator complex is compartimentalized in the perfluorocarbon. It has been shown that in such IDA methodology the fluorous phase can play the role of a membrane impervious to water, allowing the detection of histamine in water at micromolar concentrations.     

Pd-catalyzed oxidative cross-coupling of imidazo[1,2-a]pyridine with arenes

A facile method for direct Pd(OAc)₂-catalyzed oxidative cross-coupling of unactivated imidazo[1,2-a]pyridine with simple arenes has been developed. The reaction shows good reaction efficiency, high regioselectivity, and good functional-group compatibility. This approach provides a useful protocol for the preparation of imidazo[1,2-a]pyridine–arene structure of interest in biological and pharmaceutical materials.     

Alkali-metal mediated zincation of N-heterocyclic substrates using the lithium zincate complex, (THF)Li(TMP)Zn(tBu)2 and applications in in situ cross coupling reactions

This study investigates the ability of the mixed-metal reagent [Li(TMP)Zn(tBu)₂] 1 to promote direct Zn-H exchange reactions (zincations) of a wide range of N-heterocyclic molecules. The generated metallated intermediates from these reactions are intercepted with I₂ and some of them are also employed as precursors in Pd-catalysed Negishi cross-coupling applications. A comparison with recent precedents in metallation chemistry reveals that for some of these heterocycles, 1 allows improved conversions, under milder conditions and in certain cases, even gives unique regioselectivities.     

Study on molecular and electronic structures, and spectroscopic properties of azide ruthenium complexes with pyridine and β-picoline ligands

The [Ru(N₃)₂(PPh₃)(py)₃] and [Ru(N₃)₂(PPh₃)₂(β-pic)₂] complexes have been prepared and studied by IR, NMR, UV-Vis spectroscopy and X-ray crystallography. The complexes were prepared in the reactions of [RuCl₂(PPh₃)₃] with pyridine, β-picoline and NaN₃ in methanol solutions. The electronic structures of the obtained complexes have been calculated using the DFT/TD-DFT method. The trans effect of triphenylphosphine on the pyridine molecule has been studied using NBO and molecular orbital terms, and impact of the acceptor properties of the halide/pseudohalide co-ligands was indicated.     

Synthesis and characterizations of meso-disubstituted asymmetric porphycenes

A post-synthetic method has been developed to synthesize novel asymmetric porphycenes bearing two different substituents on the meso-positions. Nitration of 9-acetoxy-2,7,12,17-tetra-n-propylporphycene with AgNO₃ in CH₃COOH/CH₂Cl₂ occurs regioselectively at the 19-position of the macrocycle to give 9-acetoxy-19-nitro-2,7,12,17-tetra-n-propylporphycene (3a) which was readily converted to 9-acetoxy-19-amino-2,7,12,17-tetra-n-propylporphycene (4a) by the reduction with SnCl₂ in pyridine.     

Zur synthese einiger neuer heterocyclisch substituierter stannane

The in 2-position trimethylstannylated heterocycles are formed in good yields by reaction of the lithiated heterocycles benzothiazole, N-methylbenzimidazole, N-methylimidazole, N-methyltriazole, pyridine, chinoline and thiazole with trimethylchlorostannane. The thermolabile lithium compounds are synthesized by metallation or by metal-halogen exchange reactions according to known procedures.     

Formation and structures of Pd(II) N,S-heterocyclic carbene-pyridyl mixed-ligand complexes

Mononuclear mixed-ligand complexes of Pd(II) containing a N,S-heterocyclic carbene (NSHC) with a secondary alkyl N-substituent and pyridyl ligand, with the general formula [PdI₂(C₁₀H₁₁NS)L] (C₁₀H₁₁NS = 3-isopropylbenzothiazolin-2-ylidene; L = pyridine, 2-aminopyridine, 3-iodopyridine and 4-tert-butyl-pyridine) have been synthesized and characterized by X-ray single-crystal crystallography. Both solution and solid-state structures, as evident from their ¹H NMR spectra and X-ray structures, show anagostic γ-hydrogen interactions of metal with methine of the substituent on the carbene or pyridyl ligand giving 5-membered-chelate-like structures.     

Intramolecular metallation of o-carboranylphosphine-palladium(II) and -platinum(II) complexes

Preparation of trans-[P^cb₂MCl₂]-type complexes (P^cb= o-HCB₁₀H₁₀CCH₂PPh₂ M = Pd, Pt), which readily undergo intramolecular metallation through the BH bonds of the carborane cage to form exocyclic compounds involving a $\text{PCCBM}$ bond system, is described. Both monomeric compounds, trans-[MCl(B-P)P^cb], and bridged complexes, such as [Pd₂Cl₂(BP)₂], are formed, where (BP) is intramolecular-metallated carborane phosphine. The bridging bond is readily cleaved under the action of various ligands (pyridine, PEt₃, etc.) to form monomeric compounds.     

Host-Guest Interactions and Laser Activity in AlPO4-5/Laser Dye Composites

In situ inclusion of the laser dyes coumarin 466, coumarin 7, pyridine 2 and DCM has been conducted successfully in AlPO₄-5 crystals. The charged molecule pyridine 2 interacts with the framework and leads to bundle-like morphologies with increasing dye content. Uncharged molecules (DCM, coumarin 7, coumarin 466) are included, although corresponding molecular dimensions are exceeding pore size. These dyes probably induce local defects in the pore walls of AlPO₄-5 which are healed during crystal growth leading to well-developed hexagonal prisms. Spectroscopic studies show interactions of the dyes with the solid-state matrix which are reflected by shifts of absorption and emission maxima of the dyes. For the first time, laser activity is demonstrated on a perfect hexagonal single AlPO₄-5/DCM crystal.