2-Allyl-N-benzyl substituted α-naphthylamines as building blocks in heterocyclic synthesis. New and efficient syntheses of benz[e]naphtho[1,2-b]azepine and naphtho[1,2-b]azepine derivatives

A new series of 13-acetyl-7,12-dihydro-7-ethylbenz[e]naphtho[1,2-b]azepine (4a-d) and 2-aryl-4-hydroxy-2,3,4,5-tetrahydronaphtho[1,2-b]azepine derivatives (6a-d) have been synthesized from N-allyl-N-benzyl substituted α-naphthylamines (1a-d) by utilizing aromatic amino-Claisen rearrangement, intramolecular Friedel-Crafts alkylation and intramolecular dipolar 1,3-cycloaddition nitrone-olefin reactions.     

One-pot synthesis of pH and temperature sensitive gold clusters mediated by a recombinant elastin-like polymer

Here, we described a “one-pot” synthesis of smart hybrid materials based on elastin-like recombinamers (ELRs) and gold nanoparticles. Outstandingly, the reduction of auric acid in the presence of ELR Glu15 gave biohybrid Au-Glu15. TEM analysis carried out for Au-Glu15 exhibited nano-sized gold crystals with diameter ranging from 2 to 11 nm. Furthermore, Au-Glu15 promoted the formation of linear arrangements of gold clusters in areas of low particle density. Remarkable was that analogous architectures were obtained in a control experiment carried out with Glu15 and gold nanoparticles synthesized via a citrate reduction route. Therefore, Glu15 promoted the formation of 2D linear arrangements of gold clusters that exhibited interparticle distances in the range from 10 to 40 nm. Notable were the branched nanostructures exhibited by Au-Glu15B obtained for reduced gold-ELR mixtures that exhibited a lower gold ratio. On the other hand, Au-Glu15 exhibited spectroscopic properties (UV-vis absorption) that could be modulated as function of pH and temperature of the environment as result of reversible aggregation-expansion of gold nanoparticles. Thereby, Au-Glu15 displayed remarkable features suitable for the development of stimuli responsive optical sensors and detectors for biological applications that could operate in aqueous media and under a wide range of pH’s.     

Efficient synthesis of new chiral 1,2-benzothiazin-3-one 1,1-dioxide derivatives via lateral lithiation of 3-N-mesitylenesulfonyl-1,3-oxazolidin-2-ones

Chiral 3-N-mesitylenesulfonyl-1,3-oxazolidin-2-ones 4a-e derived from (l)- and (d)-amino acids 1a-e undergo lateral lithiation with lithium diisopropylamide and TMEDA in anhydrous THF to provide new optically-active 1,2-benzothiazin-3-one 1,1-dioxide derivatives 5a-e with yields ranging from 63% to 79%.     

Thio-ether-footed resorcin[4]arenes: self-assembly in solution and interaction with gold nanoparticles as viewed by diffusion NMR

In this paper we present the synthesis and characterization of a new family of thio-ether-footed resorcin[4]arenes (2-4). Diffusion NMR was used to follow the self-assembly of 2-4 in CDCl₃ and CHCl₃ solutions. We found that all three molecules self-assemble into hexameric capsules. These capsules can accommodate both tertiary alkylamines and ammonium salts. From the diffusion NMR data we could conclude that the hexameric capsules of compounds 2-4 are of nearly equal stability and prevail in other organic solvents, such as dichloromethane and benzene but not in tetrahydrofuran (THF). By measuring the diffusion coefficients of 2-4 in different concentrations, we found that further aggregation, beyond the hexameric aggregates, is obtained, especially in the case of 2 at high concentrations. Different diffusion NMR techniques revealed that water molecules are part of the hexameric capsules of 2-4 in chloroform solutions. In addition diffusion NMR was used to examine the interactions of compounds 2-4 with gold nanoparticles in chloroform solution and provided an unequivocal evidence for the attachment of 2-4 to the surface of gold nanoparticles. No evidence was found for the formation of higher aggregates on the gold nanoparticles.     

The first synthesis and X-ray structures of polyfluorinated 1,2-, 2,3- and 2,4a-dihydro-1,3-diazafluorenes

Acetic acid-catalyzed condensation of 2-amino-3-(1-imino-2,2,2-trifluoroethyl)-1,1,4,5,6,7-hexafluoroindene (1b) with acetone and cyclopentanone gives 5,6,7,8,9,9-hexafluoro-2,2-dimethyl-4-trifluoromethyl-2,3-dihydro-1,3-diazafluorene (2a) and 5,6,7,8,9,9-hexafluoro-4-trifluoromethyl-2,3-dihydro-1,3-diazafluorene-2-spiro-1′-cyclopentane (3a) together with small amounts of 5,6,7,8,9,9-hexafluoro-2,2-dimethyl-4-trifluoromethyl-1,2-dihydro-1,3-diazafluorene (2b) and 5,6,7,8,9,9-hexafluoro-4-trifluoromethyl-1,2-dihydro-1,3-diazafluorene-2-spiro-1′-cyclopentane (3b), respectively. When acted upon by (CH₃)₂SO₄ compounds 2, 3 were converted into corresponding fluorine-containing 1-methyl-1,2-dihydro-1,3-diazafluorenes 6, 7. 4a-Chloro-5,6,7,8,9,9-hexafluoro-2,2-dimethyl-4-trifluoromethyl-2,4a-dihydro-1,3-diazafluorene (8) has been synthesized by the interaction of compound 2 with SOCl₂. Solution of compound 2 as well as 8 in CF₃SO₃H-CD₂Cl₂ generated 5,6,7,8,9,9-hexafluoro-2,2-dimethyl-4-trifluoromethyl-1,2,3,4-tetrahydro-1,3-diazafluorene-4-yl cation (2c). The structures of compounds 2, 3, 6-8 have been determined by single crystal X-ray diffraction.     

PhP-PPh group bound to 1,8-positions of naphthalene: Preparation of cis isomer and synthesis of binuclear complex

A thermodynamically less stable cis isomer of 1,2-diphosphacycle was prepared from the corresponding trans isomer. Diphosphine, in which a PhP-PPh bond bridges the 1,8-positions of naphthalene, 1,2-diphenyl-1,2-dihydronaphtho[1,8-cd][1,2]diphosphole (1), was first prepared according to a previously reported method, and the trans isomer of 1 was irradiated in tetrahydrofuran with UV-vis light to reach equilibrium with cis-1 in a trans:cis ratio of 1:2. When a similar photochemical conversion was carried out using a saturated hexane solution of trans-1, cis-1 was precipitated in a good yield of 94%. The configuration of cis-1 was confirmed by X-ray analysis. Both cis- and trans-1 diphosphine ligands were used for the preparation of binuclear gold complexes. The crystal structure of (μ-cis-1)-[AuCl]₂ demonstrated that the two lone pairs of cis-1 are suitably directed for arrangement of the two gold centers in close proximity to each other. The two independent (μ-cis-1)-[AuCl]₂ molecules in the crystal were found to form a dimer through the multiple intermolecular interaction among the gold centers.     

Synthesis of a new class of azathia crown macrocycles containing two 1,2,4-triazole or two 1,3,4-thiadiazole rings as subunits

A series of new 1,2/1,3-bis[o-(N-methylidenamino-5-aryl-3-thiol-4H-1,2,4-triazole-4-yl)phenoxy]alkane derivatives 3a-d and bis[o-(N-methylidenamino-2-thiol-1,3,4-thiadiazole-5-yl)phenoxy]alkanes 6a-c were prepared by condensation of 4-amino-5-(aroyl)-4H-1,2,4-triazole-3-thiols 2a-b or 2-amino-5-mercapto-1,3,4-thiadiazole with bis-aldehydes 1a-c. Further reaction of compounds 3a-d and 6a-c with dibromoalkanes afforded the new macrocycles 5a-f and 8a-d. The cyclization does not require high dilution techniques and provides the expected azathia macrocycles in good yields, ranging from 55% to 68%.     

A one-pot synthesis and 1,3-dipolar cycloaddition of [1,2]dithiolo[4,3-b]indole-3(4H)-thiones

Treatment of N-substituted 2-methyl-1H-indoles 1 with S₂Cl₂ and DABCO in chloroform gave the corresponding [1,2]dithiolo[4,3-b]indole-3(4H)-thiones 5 by the addition of triethylamine in high yield. 1,2-Dithiole-3-thiones 5 underwent cycloaddition with one or two DMAD equivalents to afford either 2-(3-thioxo-1,3-dihydro-2H-indol-2-ylidene)-1,3-dithioles 10 or fused 4,5-dihydrothiopyrano[3,2-b]indoles 9.     

Influence of the basicity of internal bases in diiron model complexes on hydrides formation and their transformation into protonated diiron hexacarbonyl form

Reaction of 2-(1-(pyridin-2-yl)ethyl)propane-1,3-dithiol with tri-iron dodecacarbonyl afforded a diiron pentacarbonyl complex, [Fe₂L(CO)₅] (A and H₂L = 2-methyl-2-(1,2,5,6-tetrahydropyridin-2-yl)propane-1,3-dithiol). In the reaction, the pyridinyl ring of the original ligand was partially hydrogenated during the reaction. This complex was fully characterised by using crystallographic, infrared, and NMR spectroscopic techniques. Formation reaction of its bridging hydride and subsequent conversion into its protonated diiron hexacarbonyl complex, [Fe₂L(CO)₆] (ACOH⁺ in which the N atom of L is decoordinated and protonated), were experimentally and theoretically investigated. Results for this complex alongside with theoretic investigations into other diiron pentacarbonyl analogues revealed positive correlation of basicity of the internal bases of these investigated complexes to bridging hydrides formation. But subsequent conversion of these bridging hydrides into protonated diiron hexacarbonyl complexes was not solely dictated by the basicity. Protophilicity of the internal base and lability of its coordination with the diiron centre play also an important role as revealed by experimental and theoretic investigations.     

N-Trifyl substituted 1,4-diheterocyclohexanes—stereodynamics and the Perlin effect

The stereodynamic behaviour of 1-(trifluoromethylsulfonyl)piperidine 1, 4-(trifluoromethylsulfonyl)morpholine 2, 1,4-bis(trifluoromethylsulfonyl)piperazine 3 and 4-(trifluoromethylsulfonyl)thiomorpholine 1,1-dioxide 4 was studied by low-temperature ¹H, ¹³C and ¹⁹F NMR spectroscopies. In acetone solution, compounds 1, 2 and 4 were found to exist as mixtures of two conformers in the ratio of 4:1, 4:1 and 8:1, respectively, differing by orientation of the CF₃ group with respect to the ring. Compound 3 exists as a mixture of three conformers in the ratio of 3:28:69 also differing by the orientation of the two CF₃ groups. Unlike the previously studied N-trifyl substituted 1,3,5-triheterocyclohexanes, the preferred conformers of compound 1 and of 1,4-diheterocyclohexanes 2-4 are those with the CF₃ group directed outward from the ring, which is caused by intramolecular interactions of the oxygen atoms of the CF₃SO₂N groups with the equatorial hydrogens in the α-position. B3LYP/6-311+G(d,p) calculations of the energy, geometry and NMR parameters corroborate the experimental data. The calculated Perlin effects for all conformers of compounds 1-4 as well as those measured for the major conformers of compounds 3 and 4 were analyzed by the use of the NBO analysis.     

On the reactivity of some 2-methyleneindolines with β-nitroenamines, α-nitroalkenes, and 1,2-diaza-1,3-butadienes

A study of the behaviour of some electron-rich 2-methyleneindolines (1-3) with different electron-poor reagents (formation of new carbon-carbon and nitrogen-carbon bonds) has furnished interesting results from both synthetic and the mechanistic viewpoints. Enamines 1-3 have been reacted with the β-nitroenamines 4-7 (reaction CeCl₃·7H₂O promoted), giving the polymethine dyes 14-23. The same bases 1-3 have been nitroalkylated with the nitroolefins 8-10, furnishing the indolines 24-32, and the diastereoselectivity of the reaction has been thoroughly investigated. The most unexpected results derived from the first example of reaction of Fischer's bases with 1,2-diaza-1,3-butadienes. In fact, with 11-13, the ‘unknown’ indoline spirodihydropyrroles 33-40 were formed. Their structures were unambiguously assigned, and we determined, as an example, that of 33 by X-ray analysis.     

Reactions of bis(tetrazole)phenylenes. Surprising formation of vinyl compounds from alkyl halides

The reactions of 1,2-bis(tetrazol-5-yl)benzene (1), 1,3-bis(tetrazol-5-yl)benzene (2), 1,4-bis(tetrazol-5-yl)benzene (3), 1,2-(Bu₃SnN₄C)₂C₆H₄ (4), 1,3-(Bu₃SnN₄C)₂C₆H₄ (5) and 1,4-(Bu₃SnN₄C)₂C₆H₄ (6) with 1,2-dibromoethane were carried out by two different methods in order to synthesise pendant alkyl halide derivatives of the parent bis-tetrazoles. This lead to the formation of several alkyl halide derivatives, substituted at either N1 or N2 on the tetrazole ring, as well as the surprising formation of several vinyl derivatives. The crystal structures of both 1,2-[(2-vinyl)tetrazol-5-yl)]benzene (1-N,2-N′) (1b) and 1,3-bis[(2-bromoethyl)tetrazol-5-yl]benzene (2-N,2-N′) (5d) are discussed.     

Efficient synthesis of novel dipyridoimidazoles and pyrido[1′,2′;1,2]imidazo[4,5-d]pyridazine derivatives

Novel dipyrido[1,2-a;3′,4′-d]imidazoles 7a-d, dipyrido[1,2-a;4′,3′-d]imidazoles 8a,c and pyrido[1′,2′;1,2]imidazo[4,5-d]pyridazine derivatives 9a-d were synthesized by two pathways: thermal electrocyclic reaction of 3-alkenylimidazopyridine-2-oximes 10 and direct condensation of ethyl glycinate (or hydrazine) with 2,3-dicarbonylimidazo[1,2-a]pyridines 11.     

Gas-phase pyrolysis of benzimidazole derivatives: novel route to condensed heterocycles

Gas-phase pyrolysis of N-(1H-benzimidazol-2-yl)-N′-arylidenehydrazines 1a-e gave the corresponding arylnitriles 2a-e, 2-aminobenzimidazole 3, 2,4,5-triphenylimidazole 4, 1,3-diphenyl-8H-2,3a,8-triazacyclopenta[a]indene 5, and 5,11-diphenyl-6H,12H-dibenzimidazo[1,2-a];1’,2’-d]pyrazine 6. The kinetics and analysis of the products of reaction are reported and used to elucidate the mechanism of the elimination process.     

Carbenoid induced irreversible ring opening of naphthopyrans

Contrary to expectation rhodium carbenoids do not undergo cycloaddition to the 2H-pyran unit of the isomeric naphthopyrans 3 and 5. With 3, a naphtho[2,1-b]pyran-8-ylacetate, 4 is formed and a novel merocyanine dye 6 results from a cycloaddition across the C-5-C-6 double bond of the naphtho[1,2-b]pyran 5. Tethering the carbenoid to the naphtho[1,2-b]pyran system 5, as in 10, results in a similar mode of addition and affords the intensely coloured tetracycle 11.     

Synthesis of 2,3-dihydroimidazo[1,2-a]pyrimidin-5(1H)-ones by the domino Michael addition retro-ene reaction of 2-alkoxyiminoimidazolidines and acetylene carboxylates

2-Alkoxyiminoimidazolidines 2-3 react with acetylene dicarboxylates and ethyl phenylpropiolate to give 8-alkoxy-imidazo[1,2-a]pyrimidin-5(3H)-ones C, which subsequently undergo a sterically induced multihetero-retro-ene fragmentation to give imidazo[1,2-a]pyrimidin-5(1H)-ones 4-7 together with formaldehyde or benzaldehyde. On the other hand, a similar reaction of 2-3 with ethyl propiolate gives corresponding 8-alkoxy-imidazo[1,2-a]pyrimidin-5(3H)-ones 8-10. The unsubstituted imidazo[1,2-a]pyrimidin-5(1H)-one 11 can be prepared by retro-ene reaction of 9 upon prolonged heating in refluxing ethanol. A direct synthetic approach to 1-formyl-7-phenyl-imidazo[1,2-a]pyrimidine-5(1H)-one 14 is reported using DMF/sulfonyl chloride as a new Vilsmeier-type N-formylating reagent.     

A new approach to 2,2-disubstituted 1-(methylsulfanyl)vinyl phosphonates via an intermediate thiocarbonyl ylide

The reaction of methyl (diethylphosphoryl)dithioformate (6) with diaryldiazomethanes 7a-d in THF at −60 °C to room temperature followed by desulfurization is shown to be a convenient method for the preparation of 2,2-disubstituted 1-(methylsulfanyl)vinyl phosphonates 8a-d. The analogous reactions with 2-diazoacenaphthen-1-one (7f) or 2-diazocamphor (7g) in refluxing THF yield selectively the corresponding (Z)- and (E)-vinyl phosphonates 8f and 8g, respectively. These products can be easily oxidized to the vinylsulfoxides 13 and vinylsulfones 14. On the other hand, methyl (diethylphosphoryl)dithioformate (6) and 2-diazo-1,2-diphenylethanone (7e) in boiling THF react to give the 1,3-oxathiole 12. All these reactions occur via an intermediate thiocarbonyl ylide 11 followed by 1,3-dipolar electrocyclization and sulfur extrusion or 1,5-dipolar electrocyclization.     

Synthesis and reactions of 3-alkylsulfanyl-1,3-dihydro-2,1-benzisothiazole 2,2-dioxides

Alkyl- and arylsulfanylation of 1,3-dihydro-2,1-benzisothiazole 2,2-dioxides (benzosultams) 1a-c and pyridosultam 1d with dialkyl and diaryl disulfides provides dithioacetals of 2-aminobenzaldehydes 6-13. 1,3-Dimethylbenzosultam 19 with disulfides forms 3-alkyl(aryl)sulfanyl-1,3-dimethylbenzosultams 20-22 that undergo thermal extrusion of SO₂ followed by a [1,5] sigmatropic hydrogen shift in the intermediate aza-ortho-xylylene leading to 1-arylvinyl sulfides 24-26. Tandem alkylation-sulfanylation of benzo- and pyridosultams 1a-d with 4-bromobutyl thiocyanate gives tetrahydrothiopyrano-spiro-benzosultams 27-30 that, after extrusion of SO₂ and [1,5] hydrogen shift, form 2-aryl-5,6-dihydro-4H-thiopyrans 32-35. Alkylation of pyridosultam 1d with 3-chloropropyl thiocyanate leads directly to 2-pyrido-3,4-dihydrothiophene derivative 37.     

Synthesis and properties of 3-arylcyclohepta[4,5]imidazo[1,2-a]-1,3,5-triazine-2,4(3H)-diones and related compounds: photo-induced autorecycling oxidation of some amines

Novel 3-phenyl- and 3-(4-nitrophenyl)cyclohepta[4,5]imidazo[1,2-a]-1,3,5-triazine-2,4(3H)-diones and the corresponding imino derivatives 5a,b and 6a,b were synthesized in modest to moderate yields by the abnormal and normal aza-Wittig reaction of 2-(1,3-diazaazulen-2-ylimino)triphenylphosphorane with aryl isocyanates and subsequent heterocyclization reaction with a second isocyanate. The related cationic compound, 1-methyl-3-phenylcyclohepta[4,5]imidazo[1,2-a]-1,3,5-triazine-2,4(3H)-dionylium tetrafluoroborate 7a, was also prepared. The electrochemical reduction of these compounds exhibited more positive reduction potentials as compared with those of the related compounds of 3,10-disubstituted cyclohepta[4,5]pyrrolo[2,3-d]pyrimidine-2,4(1H,3H)-dione systems. In a search of the oxidizing ability, compounds 5a, 6a, and 7a were demonstrated to oxidize some amines to give the corresponding imines in more than 100% yield under aerobic and photo-irradiation conditions, while even benzylamine was not oxidized under aerobic and thermal conditions at 100 °C. The oxidation reactions by cation 7a are more efficient than that by 5a and 6a. Quenching of the fluorescence of 5a was observed, and thus, the oxidation reaction by 5a probably proceeds via electron-transfer from amine to the excited singlet state of 5a. In the case of cation 7a, the oxidation reaction is proposed to proceed via formation of an amine-adduct of 7a and subsequent photo-induced radical cleavage reaction.     

Synthesis,structural analysis,and thermal and spectroscopic studies of methylmalonate-containing zinc(II) complexes

The synthesis, crystal structure, thermal analysis and spectroscopic studies of five zinc(II) complexes of formulae [Zn(Memal)(H₂O)]_n (1) and [Zn₂(L)(Memal)₂(H₂O)₂]_n (2-5) [H₂Memal = methylmalonic acid, and L = 4,4′-bipyridine (4,4′-bpy) (2), 1,2-bis(4-pyridyl)ethylene (bpe) (3), 1,2-bis(4-pyridyl)ethane (bpa) (4) and 4,4′-azobispyridine (azpy) (5)] are presented here. The crystal structure of 1 is a three-dimensional arrangement of zinc(II) cations interconnected by methylmalonate groups adopting the μ₃-κ²O:κO’:κO”:κO”’ coordination mode to afford a rare (10,3)-d utp-network. The structures of the compounds 2-5 are also three-dimensional and they consist of corrugated square layers of methylmalonate-bridged zinc(II) ions which are pillared by bis-monodentate 4,4′-bpy (2), bpe (3), bpa (4) and azpy (5) ligands. The Memal ligand in 2-5 adopts the μ₃-κO:κO′:κO′′:κO′′′ coordination mode. Each zinc(II) ion in 1-5 is six-coordinated with five (1)/four (2-5) methylmalonate-oxygen atoms, a water molecule (1-5) and a nitrogen atom from a L ligand (2-5) building distorted octahedral environments. The rod-like L co-ligands in 2-5 appear as useful tools to control the interlayer metal-metal separation, which covers the range 8.4311(5) Å (2) – 9.644(3) Å (5). The influence of the co-ligand on the fluorescence properties of this series of compounds has been analyzed and discussed by steady-state and time resolved spectroscopy on all five compounds in the solid state.