RESUMEN
The acid-promoted cyclization of all-trans linearly conjugated dienones and dienals constitutes a synthetic strategy for the construction of 2-cyclopentenones.
Asunto(s)
Ácidos , Ciclopentanos , Ciclización , Catálisis , EstereoisomerismoRESUMEN
A series of synthetic 1,2,4-trioxanes related to artemisinin was tested against L. donovani and T. cruzi parasites. This screening identified some active compounds, with key common structural features. Interestingly, these selected trioxanes were efficient against both parasites, and achieved antiparasitic activities comparable or superior than those presented by the corresponding reference drugs, artemisinin and artesunate. This study represents the first example of synthetic trioxanes evaluated on T. cruzi and provides possible candidates for developing new drugs for the treatment of leishmaniasis and Chagas disease.
Asunto(s)
Antiparasitarios/farmacología , Compuestos Heterocíclicos/farmacología , Leishmania donovani/efectos de los fármacos , Trypanosoma cruzi/efectos de los fármacos , Antiparasitarios/síntesis química , Antiparasitarios/química , Relación Dosis-Respuesta a Droga , Compuestos Heterocíclicos/síntesis química , Compuestos Heterocíclicos/química , Estructura Molecular , Pruebas de Sensibilidad Parasitaria , Relación Estructura-ActividadRESUMEN
A stereoselective multicomponent reaction involving Meldrum's acid, a conjugated dienal, and an alcohol is reported. Valuable cyclopenta[ b]furan-2-ones are obtained as products of this straightforward transformation, which is accompanied by the formation of four stereocenters, two new cycles, and four new bonds (two C-C and two C-heteroatom). A reaction mechanism was elaborated involving an initial Knoevenagel condensation followed by cycloisomerization and eventual fragmentation.
RESUMEN
The gold-catalyzed intermolecular hydroalkylation of olefins with ß-ketoesters represents a conceptually attractive and useful synthetic tool; however, it has been scarcely applied, remaining a challenge for chemists. The aim of the current study was to investigate the addition of these 1,3-diketo-compounds to alkenes under gold catalysis conditions, in order to establish the electronic and steric effects of the alkenyl substrates in the reaction outcome. The screening of different catalyst systems and diverse olefins enabled defining the alkenyl requirements and the best reaction conditions to efficiently achieve the coupled products.
Asunto(s)
Alquenos/química , Ésteres/química , Oro/química , Cetonas/química , Catálisis , Estructura Molecular , Espectroscopía de Protones por Resonancia Magnética , EstereoisomerismoRESUMEN
The control of the connectivity between nodes of synthetic networks is still largely unexplored. To address this point we take advantage of a simple dynamic chemical system with two exchange levels that are mutually connected and can be activated simultaneously or sequentially. Dithioacetals and disulfides can be exchanged simultaneously under UV light in the presence of a sensitizer. Crossover reactions between both exchange processes produce a fully connected chemical network. On the other hand, the use of acid, base or UV light connects different nodes allowing network rewiring.
RESUMEN
The synthesis of biologically active alkaloid benzosimuline, isolated from the shrub Zanthoxylum simulans, is reported. Key transformation involves an oxa-6π electrocyclic ring-opening/hetero-Diels-Alder pericyclic cascade. Although the last aromatization step proved to be cumbersome, this work unfolds a unique route to access interesting molecules from simple precursors.
Asunto(s)
Alcaloides/síntesis química , Benzopiranos/química , Reacción de Cicloadición , Análisis Espectral/métodos , Estereoisomerismo , Zanthoxylum/químicaRESUMEN
A gold-catalyzed cyclization of immobilized 2-alkynylanilines was developed as the key step in the synthetic sequence for the preparation of 2-substituted indoles. These results demonstrate the potential of the unexplored combination of gold catalysis and solid-phase organic synthesis.
Asunto(s)
Oro/química , Indoles/síntesis química , Catálisis , Ciclización , Estructura MolecularRESUMEN
A simple one-pot method to prepare dioxabicyclo[2.2.1] heptane derivatives, from readily available 1,2,4-trioxane frameworks, under catalytic hydrogenation conditions over a platinum surface is reported. The overall transformation involves the hydrogenation of the double bond and a ring contraction rearrangement that presumably proceeds via a hydrogenolytic cleavage of the O-O bond and subsequent intramolecular ketalization. The strategy was successfully applied to the synthesis of a Riesling acetal.
Asunto(s)
Acetales/síntesis química , Piranos/química , Compuestos Bicíclicos con Puentes/síntesis química , Compuestos Epoxi/química , Heptanos/síntesis químicaRESUMEN
The steady-state UVA (350 nm) photolysis of (E)-beta-ionone (1) in aerated toluene solutions was studied by (1)H NMR spectroscopy. The formation of the 1,2,4-trioxane (2) and 5,8-endoperoxide (5) derivatives in the ratio of 4:1 was observed. Time-resolved laser induced experiments at 355 nm, such as laser-flash photolysis, photoacoustic and singlet oxygen (1)O(2) phosphorescence detection, confirmed the formation of the excited triplet state of 1 with a quantum yield Phi(T) = 0.50 as the precursor for the generation of singlet oxygen (1)O(2) (Phi(Delta) = 0.16) and the isomeric alpha-pyran derivative (3), which was a reaction intermediate detected by NMR. In turn, the reaction of (1)O(2) with 1 and 3 occurred with rate constants of 1.0 x 10(6) and 2.5 x 10(8) M(-1)s(-1) to yield the oxygenated products 5 and 2, respectively, indicating the relevance of the fixed s-cis configuration in the alpha-pyran ring in the concerted [2+4] cycloaddition of (1)O(2).