Mateo Alajarin

New methodology for the preparation of quinazoline derivatives via tandem aza-wittig/heterocumulene-mediated annulation. Synthesis of 4(3H)-quinazolinones, benzimidazo[1,2-c] quinazolines, quinazolino[3,2-a]quinazolines and benzothiazolo[3,2-c]quinazolines

Abstract The aza-Wittig reaction of iminophosphoranes derived from N-substituted o-azidobenzamides, 2-(o-azidophenyl)-benzimidazole, -benzothiazole or -3,1-benzoxazin-4-one with heterocumulenes leads to functionalized quinazolines. Iminophosphoranes 9 , derived from N-substituted o-azidobenzamides, react under mild conditions with isocyanates to form 4H-3,1-benzoxazine-4-imines 11 which are converted into 2-substituted-4(3H)-quinazolinones 12 . Iminophosphoranes 9 also react with carbon disulfide and carbon dioxide to give the quinazolinones 13 and 14 respectively. Iminophosphorane 26 , derived from 2-(o-azidophenyl)benzimidazole, reacts with isocyanates, carbon disulfide and carbon dioxide to form 6-substituted benzimidazo[1,2-c]quinazolines 27, 28 and 29 respectively. In benzene at room temperature, iminophosphorane 31 , reacts with isocyanates yielding quinazolino[3,2-a]quinazolines 34 . Compounds 34 can also be prepared from iminophosphorane 36 and isocyanates. Iminophosphorane 40 derived from 2-(o-azidophenyl)benzothiazole reacts with aliphatic and aromatic isocyanates or isothiocyanates to give 7H-benzothiazolo[3,2-c]quinazoline-7-imines 42 . Iminophosphorane 40 also reacts with carbon dioxide or carbon disulfide to afford the corresponding isocyanate 43 or isothiocyanate 44 . The molecular structures of 11d and 42a have been determined by X-ray diffraction methods.

Azodicarboxamides as template binding motifs for the building of hydrogen-bonded molecular shuttles.

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.

New methodology for the preparation of pyrrole and indole derivatives via iminophosphoranes:synthesis of pyrrolo[1,2-a]quinoxalines, indolo[3,2-c]quinolines and indolo[1,2-c]quinazolines

Abstract The aza-Wittig reaction of iminophosphorane N-[o-(triphenylphosphoranylidene)amino]-phenyl pyrrole 4 with heterocumulenes leads to functionalized pyrrolo[l,2-a]quinoxalines. Iminophosphorane 19 , derived from 2-(o-amino)phenyl indole, reacts under mild conditions with isocyanates to form 21 which are converted into 5-amino-11H-indolo[3,2-c]quinolines 22 . Iminophosphorane 19 also reacts with carbon dioxide and carbon disulfide to give indolo[3,2-c]quinolines 23 . Iminophosphorane 28 . derived from 2-fo-azido)-phenyl-3-phenyl indole, reacts with isocyanates, carbon dioxide and carbon disulfide to form indolo[l,2-c]-quinazolines 29 and 30 respectively.

Salicylate-selective electrode based on a biomimetic guanidinium ionophore.

A biomimetic strategy was employed in the development of oxoanion-selective ionophores containing the guanidinium functional group. These ionophores mimic the selective interaction observed between arginine residues of proteins and oxoanions. In previous work, it was demonstrated that a structurally rigid guanidinium ionophore exhibited excellent hydrogen sulfite selectivity (Anal. Chem. 1994, 66, 3188-3192). Herein, we describe guanidinium-containing ionophores that are selective for the oxoanion salicylate. The ability to rationally design anion-selective electrodes through this biomimetic strategy, and to both alter selectivity and improve response characteristics through structural changes to the ionophore, has been demonstrated. (1)H-NMR complexation and modeling studies were used to examine and correlate the selectivity observed with the structure of the guanidinium compounds.

Tandem 1,5-Hydride Shift/1,5-S,N-Cyclization with Ethylene Extrusion of 1,3-Oxathiolane-Substituted Ketenimines and Carbodiimides. An Experimental and Computational Study†

Under thermal activation in solution, N-[2-(1,3-oxathiolan-2-yl)]phenyl ketenimines and carbodiimides were converted into 2,1-benzisothiazol-3-ones bearing a pendant N-styryl or imidoyl fragment, respectively. These processes should occur with the concomitant formation of ethylene as result of the fragmentation of the 1,3-oxathiolane ring. The conversions of ketenimines took place under softer thermal conditions, toluene 110 degrees C, than those of carbodiimides, o-xylene 160 degrees C. A computational DFT study unveiled the mechanistic course of these transformations, rare tandem processes consisting of an initial 1,5-hydride shift of the acetalic hydrogen atom to the central carbon atom of the heterocumulene function leading to the respective o-azaxylylene. This transient intermediate then converts, in a single step, into ethylene and the experimentally isolated benzisothiazolone. This latter stage of the mechanism is rather peculiar, combining a 1,5-cyclization by S-N bond formation, aromaticity recovery at the benzene nucleus, and the fragmentation of the oxathiolane framework originating a new carbonyl group. It can be related with a vinylogous retro-ene reaction and shows pseudopericyclic characteristics. The computations also revealed that the alternative 6pi electrocyclization of the transient o-azaxylylenes cannot compete, on kinetic and thermodynamic grounds, with the experimentally observed reaction channel. The two alternative reaction paths of a number of ketenimines and carbodiimides were computationally scrutinized, the results being in accord with the experimental outcomes. In addition, sulfur extrusion from the benzisothiazolones by the action of triphenylphosphine under two different reaction conditions led to three different types of heterocyclic products, 4(3H)-quinolones, quinolino[2,1-b]quinazolin-5,12-diones, and dibenzo[b,f][1,5]diazocin-6,12-diones, whose formation is explained by the initial formation of an intermediate imidoylketene. This reactive species could be trapped by a nucleophilic solvent, ethanol.

First radical addition onto ketenimines: a novel synthesis of indoles

A novel radical-mediated synthesis of 2-alkyl indoles is described. The method is a nonchain process based on the intramolecular addition of benzylic radicals onto the central carbon atom of a ketenimine function, resulting in a 5-exo-dig cyclization.

Intramolecular addition of benzylic radicals onto ketenimines. Synthesis of 2-alkylindoles

The inter- and intramolecular addition of free radicals onto ketenimines is studied. All the attempts to add intermolecularly several silicon, oxygen or carbon centered radicals to N-(4-methylphenyl)-C,C-diphenyl ketenimine were unsuccessful. In contrast, the intramolecular addition of benzylic radicals, generated from xanthates, onto the central carbon of a ketenimine function with its N atom linked to the ortho position of the aromatic ring occurred under a variety of reaction conditions. These intramolecular cyclizations provide a novel radical-mediated synthesis of 2-alkylindoles.

Surpassing Torquoelectronic Effects in Conrotatory Ring Closures: Origins of Stereocontrol in Intramolecular Ketenimine–Imine [2+2] Cycloadditions

Unexpectedand almost perfect stereochemical control is obtained in the title reactions [Eq. (a)], although torquoelectronic theory predicts negligible stereoselection. According to ab initio and DFT calculations, this stereocontrol is determined by the geometry of the first transition state of the stepwise mechanism. In good agreement with the model proposed, the presence of an additional methylene group attached to the iminic nitrogen atom promotes a significant loss of stereocontrol.

Heterocyclic synthesis via a tandem aza-Wittig reaction/heterocumulene-mediated annulation reaction. New methodology for the preparation of quinazoline derivatives.

Abstract The aza-Wittig reaction of iminophosphoranes derived fromN-substituted o-azidobenzamides or 2-(o-azido) phenyl benzimidazolewith isocyanates, carbon dioxide or carbon disulphide, lead tofunctionalized 4(3H)-quinazolinones and benzimidazo [1,2-c]quinazolines respectively.

Thermal cyclization of phenylallenes that contain ortho-1,3-dioxolan-2-yl groups: new cascade reactions initiated by 1,5-hydride shifts of acetalic H atoms.

A series of 2-(1,3-dioxolan-2-yl)phenylallenes that contained a range of substituents (alkyl, aryl, phosphinyl, alkoxycarbonyl, sulfonyl) at the cumulenic C3 position were prepared by using a diverse range of synthetic strategies and converted into their respective 1-(2-hydroxy)-ethoxy-2-substituted naphthalenes by smooth thermal activation in toluene solution. Electron-withdrawing groups at the C3 position accelerated these tandem processes, which consisted of 1) an initial hydride-like [1,5]-H shift of the acetalic H atom onto the central cumulene carbon atom; 2) a subsequent 6π-electrocyclic ring-closure of the resulting reactive ortho-xylylenes; and 3) a final aromatization step with concomitant ring-opening of the 1,3-dioxolane fragment. If the 1,3-dioxolane ring of the starting allenes was replaced by a dimethoxymethyl group, the reactions led to mixtures of two disubstituted naphthalenes, which were formed by the migration of either the acetalic H atom or the methoxy group, with the latter migration occurring to a lesser extent. Two of the final 1,2-disubstituted naphthalenes were converted into their corresponding naphtho-fused dioxaphosphepine or dioxepinone through an intramolecular transesterification reaction. A DFT computational study accounted for the beneficial influence of the 1,3-dioxolane fragment on the carbon atom from which the H-shift took place and also of the electron-withdrawing substituents on the allene terminus. Remarkably, in the processes that contained a sulfonyl substituent, the conrotatory 6π-electrocyclization step was of lower activation energy than the alternative disrotatory mode.