Organosulfur oxidation by hydrogen peroxide using a dinuclear Mn-1,4,7-trimethyl-1,4,7-triazacyclononane complex

A mechanistic study of organosulfide oxidation by H₂O₂, using a dinuclear manganese complex as the catalyst, has revealed an unusual switch in the philicity of the oxidant for the first and the second oxygen transfer steps; this switch has been exploited to tune selectivity for each of the products.     

A pH responsive electrochemical switch sensor based on Fe(notpH3) [notpH6 = 1,4,7-triazacyclononane-1,4,7-triyl-tris(methylene-phosphonic acid)

The electrochemistry of a macrocyclic metal complex Fe(notpH₃) [notpH₆ = 1,4,7-triazacyclononane-1,4,7-triyl-tris(methylene-phosphonic acid)] reveals that the protonation/deprotonation of the non-coordinated P-OH groups in Fe(notpH₃) affects its formal potential value (E⁰′) considerably. Plotting E⁰′ as function of solution pH gives a straight line with a slope of −585 mV pH⁻¹ in the pH range of 3.4-4.0, which is about ten times larger than the theoretical value of −58 mV pH⁻¹ for a reversible proton-coupled single-electron transfer at 20 °C. A sensitive pH responsive electrochemical switch sensor is thus developed based on Fe(notpH₃) which shows an “on/off” switching at pH ∼ 4.0.     

Formation of mononuclear and polynuclear d-block metal complexes from 1,4,7-tris(3-hydroxypropyl)-1,4,7-triazacyclononane: crystal structures,spectroscopic studies,and magnetic properties

Four new d-block metal complexes formulated as [Ni^II(H3thptacn)]Cl₂·H₂O (1), [Mn^IV(thptacn)]ClO₄ (2), [Cu^II₃(Hthptacn)₂](ClO₄)₂ (3), and [Cd^II₂(H3thptacn)₂Cl₂][B(C₆H₅)₄]₂ (4) were obtained from the macrocyclic ligand 1,4,7-tris(3-hydroxypropyl)-1,4,7-triazacyclononane (H3thptacn) either through solvent diffusion or by evaporation of their solutions. These complexes were characterized by single crystal X-ray structural determination, elemental analysis, and routine spectroscopic methods. Complexes 1 and 2 exhibit similar mononuclear structures with the metal centers being surrounded by both the backbone nitrogen atoms and the pendant coordinating alcohol/alkoxide groups. Complex 3 is a linear trinuclear cluster, where three Cu(II) centers are combined together by the bridging alkoxide groups in a centro-symmetric pattern. Two chloride groups join two Cd(II) atoms each chelated by one triply protonated ligand H3thptacn to afford dinuclear compound 4 with a symmetry center. When coordinating to different d-block metals, the macrocyclic ligand exhibits four types of binding modes with various dissociation status on its pendant alcohol groups and different numbers of these pendant groups participating in coordination. The magnetic measurements revealed significant zero-field splitting for mononuclear Ni(II) and Mn(IV) complexes. A moderate antiferromagnetic interaction between the neighboring Cu(II) centers governs the magnetic properties of 3 with J = ?166(3) cm^?1.     

Synthesis,Potentiometric and 1H NMR Study of Protonation and Complex Formation of 1,4,7-Triazacyclononane-1,4-Diacetate

Abstract

Protonation constants and the protonation scheme of 1,4,7-triazacyclononone-1,4-diacetate (NO2A) have been determined by pH potentiometry and ¹H NMR techniques; shielding constants valid for the entire pH range have been calculated. It has been pointed out that the most basic site in the molecule is the unsubstituted secondary amino group. The first two protonation steps belong to ring nitrogens, the third and fourth ones to the carboxylates; the last nitrogen is protonated in very acidic solutions only. Stability constants of complexes of NO2A with selected divalent and trivalent metal ions were determined; with them no indication of kinetic inertness was found. In NO2A complexes the relative contribution of the triazacyclononane ring to the log K _ML values is greater for soft than for hard metal ions, compared to corresponding values for 1,4,7-triazacyclononane-1,4,7-triacetate.     

Synthesis and crystal structure of the first dinuclear zinc complex containing 1,4,7-triazacyclononane and biological properties of the protonated ligand

Abstract

A new binuclear complex, [Zn₂L₂Cl₄]·2H₂O {L?=?N-aldehyde-N-(4-(benzyloxy)benzyl)-1,4,7triazacyclononane}, was synthesized and characterized by X-ray, elemental analysis, infrared and electronic spectroscopy, and mass spectrometry. The central ion is bridged by the L and lies in a tetrahedral configuration with Zn···Zn distance of 6.283 Å. The complex crystallizes in the triclinic space group Pī. ESI-MS of the complex indicates that the protonated ligand HL⁺ is the active species. The interaction of HL⁺ with calf thymus–DNA (CT–DNA) and bovine serum albumin (BSA) was studied by means of various spectroscopic methods, which revealed that HL⁺ could interact with CT–DNA through groove-binding mode and could quench the intrinsic fluorescence of BSA in a static quenching process. DNA–cleavage experiments indicate that HL⁺ exhibits efficient DNA–cleavage activity in the presence of H₂O₂, hydroxyl radical (HO^?) may serve as the major cleavage active species, and the pseudo-Michaelis–Menten kinetic parameters (K_cat, K_M, V_max); 2.47?h^?1, 2.70?×?10^?4 M and 6.68?×?10^?4 Mh^?1.     

Synthesis of 5,6-dehydrokawain and some fluorinated analogues

An efficient methodology for the synthesis of 6-styrenylpyrone in a four-step sequence is reported. The reactions were performed under catalyst-free conditions with mild and affordable reagents to produce 5,6-dehydrokawain and fluorinated derivatives in good to excellent overall yields (72–86%) on a multigram scale. Two novel difluorinated derivatives are reported here for the first time.     

Synthesis and Structure of Di-N-arylpyrrolo[1,2-c;5,6-c]cyclooctanes

Di-N-arylpyrrolo[1,2-c;5,6-c]cyclooctanes were synthesized for the first time by the cyclization of N,N-dipropynylarylamines in a superbasic medium.     

Synthesis of a new family of protected 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid derivatives with thioctic acid pending arms

The synthesis and characterization of a new family of ester protected N-substituted [1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (H3DO3A) derivatives containing a pendant thioctic acid (α lipoic acid, LA) are reported. These compounds (DO3A^tBu-NLA, DO3A^tBu-NMeNLA, and DO3A^tBu-NEtNLA) are suitable for the functionalization of gold surfaces with rare-earth complexes.     

An Alternative Synthesis of the Dopaminergic Drug 2‐Amino‐1,2,3,4‐tetrahydronaphthalene‐5,6‐diol (5,6‐ADTN)

Racemic 2‐amino‐1,2,3,4‐tetrahydronaphthalene‐5,6‐diol (5,6‐ADTN; 4 ) was synthesized from 5,6‐dimethoxynaphthalene‐2‐carboxylic acid ( 14 ) in four steps (60% overall yield; Scheme). The crucial steps of the synthesis are Birch reduction of 14 to the valuable synthon 15 , Curtius reaction and carbamate formation ( 16 ), hydrogenolysis ( 17 ), and demethylation to the biologically active hydrobromide salt 18 of 4 .     

Synthesis of 5,6-Dihydrophenanthridine (DHPA) Sulfonamides and Subsequent Acid-Catalyzed Rearrangement to Diaryl Sulfones

Selective method of reduction of the ortho-nitro groups in 2,4,6-trinitrotoluene by hydrazine hydrate in the presence of FeCl₃ and charcoal has been elaborated. This method allows obtaining either 2-amino-4,6-dinitrotoluene or 2,6-diamino-4-nitrotoluene as well as 2,4,6-triaminotoluene from TNT.     

Synthesis of [5,6]-fused pyridocoumarins through aza-Claisen rearrangement of 6-propargylaminocoumarins

[5,6]-Fused pyridocoumarins are prepared through aza-Claisen rearrangement and subsequent in situ cyclization of 6-propargylaminocoumarins under microwave irradiation in the presence of boron trifluoride diethyl etherate in N,N-dimethylformamide. During this process demethoxycarbonylation is observed in the corresponding 4-carbomethoxycoumarin derivatives.     

Synthesis of novel substituted 3,8,11-triazaspiro[5,6]dodecan-7-ones

A synthesis of novel substituted 3,8,11-triazaspiro[5,6]dodecan-7-ones using a combination of solution-phase and solid-phase chemistries is described. A solution-phase approach was used to produce a key piperidine intermediate that was then incorporated into a solid-phase synthesis. The combined synthetic strategy was applied to provide a series of substituted 3,8,11-triazaspiro[5,6]dodecan-7-ones in good yield and high purity.     

Synthesis and pH-sensitive redox properties of 1,10-phenanthroline-5,6-dione complexes

Synthesis and pH-sensitive electrochemical properties of three complexes, [Cu(PD)₃] · (ClO₄)₂ · 2.25CH₃CN · 6H₂O (1), [Cu(PD)(DMSO)Cl₂] · DMSO · H₂O (2) and [Co(PD)₃] · (ClO₄)₂ · CH₃CN · 2H₂O (3) (PD=1,10-phenanthroline-5,6-dione), are reported. Single-crystal X-ray diffraction of the complexes suggest that the structure of 1 is orthorhombic, 2 triclinic and 3 orthorhombic. The electrochemical properties of free PD and the three complexes in phosphate buffer solutions in a pH range between 2 and 9 have been investigated using cyclic voltammetry. The redox potentials of these compounds are strongly dependent on the proton concentration in the range ?0.3 V ～ 0.4 V versus SCE (saturated calomel reference electrode). The reduction behavior of PD can be described from quinone species to semiquinone anion then to the fully reduced dianion. At pH < 4, the reduction of PD proceeds via 2e^?/3H⁺ processes, while at pH > 4, the reduction of PD proceeds via 2e^?/2H⁺. For all complexes, the N–N chelate PD ligand is electrochemically active and underwent step reduction via 2e^?/2H⁺.     

Synthesis of Substituted Pyrazino[5,6-b]pyrimidine and Some Indole Derivatives

Refluxing dimethyl acetylenedicarboxylate (DMAD) or 1,2-dibenzoylacetylene with isatin-3-thiosemicarbazone or isatin-3-thiocarbohydrazone in methanol produced 3-substituted oxindoles in good yields. Reaction of equimolecular amounts of 5,6-diamino-urasil-solfate, trans-(1R,2R)-diaminocyclohexane, and 3,4-diamino-1,2,4-triazol-5-methyl hydrochlorid with isatin in ethanol (85%) afforded tetracyclic ring systems and ring-opened products in mild reaction conditions.     

Synthesis of Alkyl 5,6-Dialkyl-2-amino-3-cyanopyridine-4-carboxylates

An unusual route has been found for the hydrolysis of 3-amino-1,1-dialkoxy-6,7-dialkyl-4-aryl-3a,4,5,7a-tetrahydro-1H-pyrrolo[3,4-c]pyridine-3a,7a-dicarbonitriles in acidic medium which leads to the formation of alkyl 5,6-dialkyl-2-amino-3-cyanopyridine-4-carboxylates.     

Water Stability and Luminescence of Lanthanide Complexes of Tripodal Ligands Derived from 1,4,7‐Triazacyclononane: Pyridinecarboxamide versus Pyridinecarboxylate Donors

A series of europium(III) and terbium(III) complexes of three 1,4,7‐triazacyclononane‐based pyridine containing ligands were synthesized. The three ligands differ from each other in the substitution of the pyridine pendant arm, namely they have a carboxylic acid, an ethylamide, or an ethyl ester substituent, i.e., these ligands are 6,6′,6″‐[1,4,7‐triazacyclononane‐1,4,7‐triyltris(methylene)]tris[pyridine‐2‐carboxylic acid] (H₃tpatcn), ‐tris[pyridine‐2‐carboxamide] (tpatcnam), and ‐tris[pyridine‐2‐carboxylic acid] triethyl ester (tpatcnes) respectively. The quantum yields of both the europium(III) and terbium(III) emission, upon ligand excitation, were highly dependent upon ligand substitution, with a ca. 50‐fold decrease for the carboxamide derivative in comparison to the picolinic acid (=pyridine‐2‐carboxylic acid) based ligand. Detailed analysis of the radiative rate constants and the energy of the triplet states for the three ligand systems revealed a less efficient energy transfer for the carboxamide‐based systems. The stability of the three ligand systems in H₂O was investigated. Although hydrolysis of the ethyl ester occurred in H₂O for the [Ln(tpatcnes)](OTf)₃ complexes, the tripositive [Ln(tpatcnam)](OTf)₃ complexes and the neutral [Ln(tpatcn)] complexes showed high stability in H₂O which makes them suitable for application in biological media. The [Tb(tpatcn)] complex formed easily in H₂O and was thermodynamically stable at physiological pH (pTb 14.9), whereas the [Ln(tpatcnam)](OTf)₃ complexes showed a very high kinetic stability in H₂O, and once prepared in organic solvents, remained undissociated in H₂O.     

O,N-Dimethylation of 5,6-dihydroxynicotinic acid

AnO,N-dialkylation product, 1-methyl-5-metlioxy-6-oxo-1,6-diliydropyridine-3 carboxylic acid, is formed in the reaction of 5,6-dihydroxynicotinic acid with dimethylsulfate.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1554–1555, June, 1996.     

An Efficient Synthesis of 5,6‐Dimethoxy 1‐ and 2‐Naphthols via Teuber Reaction

Based on the oxidation of 1,5‐naphthalenediol ( 4 ) and 6‐bromo‐2‐naphthol ( 9 ) via Teuber reaction, an efficient synthesis of 5,6‐dimethoxy‐1‐naphthol ( 1 ) and 5,6‐dimethoxy‐2‐naphthol ( 2 ) was achieved with high overall yield (16% for 1 and 25% for 2 ). The key steps of the synthetic strategy involved the oxidation of naphthols ( 4 and 9 ) to the corresponding naphthoquinones ( 5 and 10 ) and the conversion of 5,6‐dimethoxy‐2‐naphthaldehyde to 5,6‐dimethoxy‐2‐naphthol formate through Baeyer‐Villiger oxidation‐rearrangement.     

Synthesis of substituted 2-amino-5,6-dihydropyrimidin-4-ones using an aza-Wittig reaction

An aza-Wittig reaction has been used for the first time in the synthesis of substituted 2-amino-5,6-dihydropyrimidin-4-ones via condensation of triphenyliminophosphoranes with aromatic heterocumulenes (arylisocyanates and thiocyanates). __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 1037–1041, July, 2006.