RESUMEN
This work describes the unprecedented intramolecular cyclization occurring in a set of α-azido-ω-isocyanides in the presence of catalytic amounts of sodium azide. These species yield the tricyclic cyanamides [1,2,3]triazolo[1,5-a]quinoxaline-5(4H)-carbonitriles, whereas in the presence of an excess of the same reagent, the azido-isocyanides convert into the respective C-substituted tetrazoles through a [3 + 2] cycloaddition between the cyano group of the intermediate cyanamides and the azide anion. The formation of tricyclic cyanamides has been examined by experimental and computational means. The computational study discloses the intermediacy of a long-lived N-cyanoamide anion, detected by NMR monitoring of the experiments, subsequently converting into the final cyanamide in the rate-determining step. The chemical behavior of these azido-isocyanides endowed with an aryl-triazolyl linker has been compared with that of a structurally identical azido-cyanide isomer, experiencing a conventional intramolecular [3 + 2] cycloaddition between its azido and cyanide functionalities. The synthetic procedures described herein constitute metal-free approaches to novel complex heterocyclic systems, such as [1,2,3]triazolo[1,5-a]quinoxalines and 9H-benzo[f]tetrazolo[1,5-d][1,2,3]triazolo[1,5-a][1,4]diazepines.
Asunto(s)
Azidas , Cianuros , Azidas/química , Ciclización , Estructura Molecular , Cianamida , Quinoxalinas/químicaRESUMEN
By virtue of its alkylidenecyclopropane moiety, 2-(cyclopropylidenemethyl)benzaldehyde reacts with a range of amines and thiols under Lewis acid catalysis. These reactions yield 1,3-bis(arylamino) and 1,3-bis(arylthio and alkylthio)indanes, respectively, which are spirolinked to the cyclopropane ring at carbon 2. The reaction mechanism, and the peculiar contribution of the cyclopropane ring, have been scrutinized via DFT calculations.
RESUMEN
Macrocyclic bis(thioureas) derived from 2,2'-biphenyl and binaphthyl skeletons have been synthesized by reaction of 2,2'-diaminobiaryl and 2,2'-bis(isothiocyanato)biaryl derivatives. The splitting of these bis(thioureas) into two units of the respective cyclic monothioureas has been monitored by NMR, shedding some light on the factors that control these processes. Additionally, a computational study revealed up to three mechanistic paths for the conversion of the 2,2'-biphenyl-derived bis(thiourea) into the corresponding monothiourea. The proposed mechanisms account for the participation of a molecule of water as an efficient proton-switch as well as for different classes of putative intermediates. The computational study also supports the ability of the thiourea group to participate in a plethora of processes, such as prototropic equilibria, sigmatropic shifts, heteroene and retro-heteroene reactions, and cis â trans isomerizations.
RESUMEN
We describe the incorporation of endo-pyridine units into the tetralactam ring of di(acylamino)pyridine-based rotaxanes. This macrocycle strongly associates with the linear interlocked component as confirmed by X-ray diffraction studies of rotaxane 2 b. Dynamic NMR studies of 2 b in solution revealed a rotational energy barrier that was higher than that of the related rotaxane 2 a, which lacks of pyridine rings in the macrocycle. The macrocycle distribution of the molecular shuttle 4 b, containing two endo-pyridine rings, shows that the major co-conformer is that with the cyclic component sitting over the di(acylamino)pyridine station. DFT calculations also support the marked preference of the ring for occupying the heterocyclic binding site. The association of N-hexylthymine with the di(acylamino)pyridine binding site of 4 b led to the formation of a rare 'S'-shaped co-conformer in which the tetralactam ring interacts simultaneously with both stations of the thread.
RESUMEN
The [3 + 2] annulation reaction of C,C,N-trisubstituted ketenimines with donor-acceptor cyclopropanes bearing aryl, styryl and vinyl substituents at the C2 position, triggered by the Lewis acid Sc(OTf)3, supplies highly substituted pyrrolidines. Activated cyclopropanes fused to naphthalene and [1]benzopyrane nuclei are also suitable substrates in similar transformations, yielding partially saturated benz[g]indoles and [1]benzopyran[4,3-b]pyrroles. An intramolecular version of this ketenimine/cyclopropane [3 + 2] annulation has also been developed leading to the pyrrolo[2,1-a]isoindole framework.
RESUMEN
The cycloisomerization reactions of allenes bearing cyclic acetal, thioacetal and dithioacetal subunits, when triggered either by the catalytic action of AgSbF6 or by one equiv. of CF3COOH, gave rise to four different classes of indeno-fused 1,4-dioxa, oxathia and dithia heterocycles, in most cases as a single diastereomer. Acyclic acetals and dithioacetals are also suitable starting materials in similar transformations yielding 1,2-disubstituted indenes and 1,3-disubstituted 2-alkylideneindanes.
RESUMEN
Di(acylamino)pyridines successfully template the formation of hydrogen-bonded rotaxanes through five-component clipping reactions. A solid-state study showed the participation of the pyridine nitrogen atom in the stabilization of the mechanical bond between the thread and the benzylic amide macrocycle. The addition of external complementary binders to a series of interlocked bis(2,6-di(acylamino)pyridines) promoted restraint of the back and forward ring motion. The original translation can be restored through a competitive recognition event by the addition of a preorganized bis(di(acylamino)pyridine) that forms stronger ADA-DAD complexes with the external binders.
Asunto(s)
Rotaxanos/química , Sitios de Unión , Cristalografía por Rayos X , Enlace de Hidrógeno , Conformación Molecular , Piridinas/químicaRESUMEN
Tris(2- and 3-ureidobenzyl)amines with C(s) symmetry self-assemble in solution forming mixtures of regioisomeric capsular aggregates, one of which is chiral and the other centrosymmetric. Under certain conditions, a predominance of the centrosymmetric regioisomer is found before equilibrium, that is, a mixture close to the statistical ratio of the two species is reached. In the solid state, there is a preference for the centrosymmetric capsules. Molecular models of both regioisomeric aggregates have been built and analyzed for comparison. Guests inside capsules formed by self-assembly of desymmetrized tris(3-ureidobenzyl)amines feel different magnetic environments, depending on whether they are inside a chiral or an achiral regioisomeric container. Of special significance are the experiments with a more flexible triurea endowed with an ureidopropylic arm, which self-assembles with the same efficiency as the more rigid tris(ureidobenzyl)amines.
RESUMEN
A number of N-aryl ketenimines, substituted at the ortho position either with different non-cyclic acetalic functions (acetals, monothioacetals, dithioacetals) or with only one alkoxymethyl or (alkylthio)methyl group, have been prepared and submitted to thermal treatment in toluene solution. Under smooth heating the ketenimines bearing non-cyclic acetals converted into 3,4-dihydroquinolines following two competitive tandem sequences that involve the alternative 1,5 migration of a hydride or alkoxy group as the first mechanistic step, followed by subsequent 6π electrocyclic ring closure. The heterocumulenes bearing acyclic monothioacetal and dithioacetal functions converted via a unique consecutive process involving the selective migration of the alkanethiolate group. Ketenimines bearing only one ether or thioether group transformed exclusively by the tandem sequence initiated by a 1,5 hydride shift. All these transformations provided as final reaction products a variety of quinoline derivatives with a range of substitution patterns. From these experiments the following order of propensity to migration can be extracted: RS > RO > H. It was also possible to estimate the following order of relative activating activities: RO > RS > H.
RESUMEN
The synthesis and electrochemical, optical, and cation-sensing properties of the ferrocene-triazole-pyridine triads 3 and 5 are presented. Azidoferrocene 1 and 1,1'-diazidoferrocene 4 underwent the "click" reaction with 2-ethynylpyridine to give the triads 3 and 5 in 81% and 68% yield, respectively. Electrochemical studies carried out in CH(3)CN in the presence of increasing amounts of Zn(2+), Ni(2+), Cd(2+), Hg(2+), and Pb(2+) metal cations, showed that the wave corresponding to the ferrocene/ferrocenium redox couple is anodically shifted by 70-130 mV for triad 3 and 167-214 mV for triad 5. The maximum shift of the ferrocene oxidation wave was found for 5 in the presence of Zn(2+). In addition, the low-energy band of the absorption spectra of 3 and 5 are red-shifted (Δλ = 5-10 nm) upon complexation with these metal cations. The crystal structures of compounds 3 and 5 and the complex [3(2)·Zn](2+) have been determined by single-crystal X-ray methods. (1)H NMR studies as well as density functional theory calculations have been carried out to get information about the binding sites that are involved in the complexation process.
Asunto(s)
Compuestos Ferrosos/química , Compuestos Organometálicos/síntesis química , Piridinas/química , Triazoles/química , Técnicas de Química Sintética , Cristalografía por Rayos X , Electroquímica , Metalocenos , Modelos Moleculares , Estructura Molecular , Óptica y Fotónica , Compuestos Organometálicos/química , Oxidación-Reducción , EstereoisomerismoRESUMEN
The guanidine unit in the guise of 2-aminoimidazole in the new structural motif 2-arylamino-1,3-diaza[3]ferrocenophane 4 acts as a binding site for anions. The electrochemical behavior of this compound has been studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) and was found to exhibit a quasi reversible oxidation peak, associated to the Fe(II)/Fe(III) redox couple (Ep = 440 mV), and a non-reversible oxidation wave (Ep = 817 mV), probably associated to the oxidation of the CâN unit present in the guanidine bridge. Recognition of AcO(-), PhCO(2)(-), F(-), Cl(-), and Br(-) anions by the free receptor and the less basic anions Br(-), Cl(-), and NO(3)(-) by its monoprotonated form takes place by unusual redox-ratiometric measurements and spectroscopic ((1)H NMR and UV-vis) changes.
Asunto(s)
Compuestos Ferrosos/química , Sondas Moleculares/química , Aniones/química , Colorimetría , Isomerismo , Modelos Moleculares , Conformación Molecular , Oxidación-Reducción , Análisis EspectralRESUMEN
N-(2-azidomethyl)phenyl ketenimines and N-(2-azidomethyl)phenyl-N'-alkyl(aryl) carbodiimides undergo, under mild thermal conditions, intramolecular [3 + 2] cycloaddition reactions between the azido group and either the C=C or the distal C=N double bonds of the ketenimine and carbodiimide functions respectively. The reaction products are indolo[1,2-a]quinazolines and/or indolo[2,1-b]quinazolines in the case of azido-ketenimines, and tetrazolo[5,1-b]quinazolines in the case of azido-carbodiimides. The formation of the two classes of indoloquinazolines implies the ulterior dinitrogen extrusion from the non-isolated, putative [3 + 2] cycloadducts between the azide and ketenimine functions, whereas in the case of azido-carbodiimides the initial cycloadducts, tetrazoloquinazolines, were cleanly isolated and further converted into 2-aminoquinazolines by thermally induced dinitrogen extrusion.
Asunto(s)
Azidas/química , Imidas/química , Iminas/química , Quinazolinas/síntesis química , Ciclización , Estructura Molecular , Quinazolinas/química , EstereoisomerismoRESUMEN
Azodicarboxamides (R(2)NCON=NCONR(2)) are shown to act as new templates for the assembly of unprecedented azo-functionalized hydrogen-bond-assembled [2]rotaxanes. Moreover, these binding sites can be reversibly and efficiently interconverted with their hydrazo forms through a hydrogenation-dehydrogenation strategy of the nitrogen-nitrogen bond. This novel chemically switchable control element has been implemented in stimuli-responsive molecular shuttles that work through a reversible azo/hydrazo interconversion, producing large amplitude net positional changes with a good discrimination between the binding sites of the macrocycle in both states of the shuttle. These molecular shuttles are able to operate by two different mechanisms: in a discrete mode through two reversible and independent chemical events and, importantly, in a continuous regime through a catalyzed ester bond formation reaction in which the shuttle acts as an organocatalyst. In this latter, the incorporation of both states of the shuttle into this simple chemical reaction network promotes a dynamic translocation of the macrocycle between two nitrogen and carbon-based stations of the thread allowing an energetically uphill esterification process to take place.
Asunto(s)
Amidas/química , Compuestos Azo/química , Rotaxanos/síntesis química , Cristalografía por Rayos X , Enlace de Hidrógeno , Modelos Moleculares , Estructura Molecular , Rotaxanos/químicaRESUMEN
A novel carbazolocarbazole system has been evaluated as an anion receptor in DMF solution. A good affinity has been detected for oxoanions. The anion binding studies have been contrasted by different experimental techniques.
RESUMEN
The ability of triarylmethane and diarylmethane fragments to behave as hydride donors participating in thermal [1,5]-H shift/6π-ERC tandem processes involving ketenimine and carbodiimide functions is disclosed. C-Alkyl-C-phenyl ketenimines N-substituted by a triarylmethane substructure convert into a variety of 3,3,4,4-tetrasubstituted-3,4-dihydroquinolines, as structurally related carbodiimides transform into 3,4,4-trisubstituted-3,4-dihydroquinazolines via transient ortho-azaxylylenes. The first step of these one-pot conversions, the [1,5]-H shift, is considered to be a hydride migration on the basis of the known hydricity of the tri(di)arylmethane fragment and the electrophilicity of the central heterocumulenic carbon atom, whereas the final electrocyclization involves the formation of a sterically congested C-C or C-N bond. In the cases of C,C-diphenyl substituted triarylmethane-ketenimines the usual 6π-ERC becomes prohibited by the presence of two phenyl rings at each end of the azatrienic system. This situation opens new reaction channels: (a) following the initial hydride shift, the tandem sequence continues with an alternative electrocyclization mode to give 9,10-dihydroacridines, (b) the full sequence is initiated by a rare 1,5 migration of an electron-rich aryl group, followed by a 6π-ERC which leads to 2-aryl-3,4-dihydroquinolines, or (c) a different [1,5]-H shift/6π-ERC sequence involving the initial migration of a hydrogen atom from a methyl group at the ortho position to the nitrogen atom of the ketenimine function. Diarylmethane-ketenimines bearing a methyl group at the benzylic carbon atom experience a tandem double [1,5]-H shift, the first one being the usual benzylic hydride transfer whereas the second one involves the methyl group at the initial benzylic carbon atom, the reaction products being 2-aminostyrenes. Diarylmethane-ketenimines lacking such a methyl group convert into 3,4-dihydroquinolines by the habitual tandem [1,5]-H shift/6π-ERC processes.
RESUMEN
C,C,N-Triaryl ketenimines and C-alkyl-C,N-diaryl ketenimines react with 2 equiv of PTAD to provide 1,2,4-triazolo[1,2-a]cinnolines with a pendant triazolidindione group by means of a Diels-Alder/ene sequence. The treatment of such adducts with potassium hydroxide affords 3-aminocinnolines.
RESUMEN
The self-assembly of chiral tris(m-ureidobenzyl)amines to give dimeric capsules is a highly diastereoselective process in solution, while in the solid state, the formation of the corresponding capsules is not only diastereoselective but also regioselective.
Asunto(s)
Bencilaminas/síntesis química , Cristalografía por Rayos X , Dimerización , Enlace de Hidrógeno , Espectroscopía de Resonancia Magnética , Estructura Molecular , Soluciones/química , EstereoisomerismoRESUMEN
En route to a photoswitchable interlocked catalyst we have proved the ability of thiodiglycolamide to act as a template in the formation of hydrogen-bonded [2]rotaxanes. X-ray diffraction studies reveal the shielding of the sulfide atom by the macrocycle. A series of molecular shuttles are described as having an isomerizable fumaramide and thiodiglycolamide binding sites for controlling the relative ring position at will. By employing these systems as photoregulated catalysts, the TiCl4-mediated chalcogeno-Morita-Baylis-Hillman reaction is tested. In the presence of the maleamide shuttle, in which the sulfide function is encapsulated by the macrocycle, a complete loss in control of the geometry of the produced aldol is observed. The E-aldol adduct is predominantly obtained when the photoisomerized fumaramide shuttle, in which the sulfide function is exposed, is used.
RESUMEN
A cyclic network of chemical reactions has been conceived for exchanging the dynamic behaviour of di(acylamino)pyridine-based rotaxanes and surrogates. X-ray diffraction studies revealed the intercomponent interactions in these interlocked compounds and were consistent with those found in solution by dynamic NMR experiments. This particular binding site was incorporated into a molecular shuttle enabled for accessing two states with an outstanding positional discrimination through chemical manipulation. Furthermore, the ability of the di(acylamino)pyridine domain to associate with external binders with a complementary array of HB donor and acceptor sites was exploited for the advance of an unprecedented electrochemical switch operating through a reversible anion radical recognition process.
RESUMEN
A novel class of π-conjugated systems, which combine the indolo[3,2-b]carbazole unit with the formation of four-coordinate boron complexes, is presented. The resulting conjugated compounds have a double-laddered structure that provides interesting optical and electrochemical properties. The wide absorption range, covering most of the visible spectrum, along with the narrowing of the HOMO-LUMO energy gap, due to the presence of diphenylboryl centers, reinforces the potential of these molecules within the area of organic electronics.