RESUMEN
Herein, we present an operationally simple protocol for the cycloisomerization of propargylic carbamates in which a heterogeneous catalyst consisting of Pd species immobilized on amino-functionalized siliceous mesocellular foam (PdII -AmP-MCF) is used. This Pd nanocatalyst displayed high efficiency at low catalyst loading and reaction temperatures, which allowed for the efficient and mild synthesis of a wide range of 1,3-oxazolidin-2-one derivatives and related compounds. Moreover, it proved possible to re-use the Pd nanocatalyst for several reactions, although a gradual decrease in activity was observed in the subsequent cycles.
RESUMEN
Chemoselective reduction of the C=C bond in a variety of α,ß-unsaturated carbonyl compounds using supported palladium nanoparticles is reported. Three different heterogeneous catalysts were compared using 1 atm of H2 : 1)â nano-Pd on a metal-organic framework (MOF: Pd(0) -MIL-101-NH2 (Cr)), 2)â nano-Pd on a siliceous mesocellular foam (MCF: Pd(0) -AmP-MCF), and 3)â commercially available palladium on carbon (Pd/C). Initial studies showed that the Pd@MOF and Pd@MCF nanocatalysts were superior in activity and selectivity compared to commercial Pd/C. Both Pd(0) -MIL-101-NH2 (Cr) and Pd(0) -AmP-MCF were capable of delivering the desired products in very short reaction times (10-90â min) with low loadings of Pd (0.5-1â mol %). Additionally, the two catalytic systems exhibited high recyclability and very low levels of metal leaching.
RESUMEN
A simple and efficient method to prepare synthetically useful 2-arylindoles is presented, using a heterogeneous Pd catalyst and diaryliodonium salts in water under mild conditions. A remarkably low leaching of metal catalyst was observed under the applied conditions. The developed protocol is highly C-2 selective and tolerates structural variations both in the indole and in the diaryliodonium salt. Arylations of both N-H indoles and N-protected indoles with ortho-substituted, electron-rich, electron-deficient, or halogenated diaryliodonium salts were achieved to give the desired products in high to excellent isolated yields within 6 to 15 h at room temperature or 40 °C.
Asunto(s)
Hidrocarburos Aromáticos/síntesis química , Indoles/síntesis química , Yodo/química , Paladio/química , Sales (Química)/química , Catálisis , Hidrocarburos Aromáticos/química , Indoles/química , Nanoestructuras/química , Nanoestructuras/ultraestructuraRESUMEN
Cycloisomerization of various γ-acetylenic acids to their corresponding γ-alkylidene lactones by the use of a heterogeneous Pd(II) catalyst supported on amino-functionalized siliceous mesocellular foam is described. Substrates containing terminal as well as internal alkynes were cyclized in high to excellent yields within 224 h under mild reaction conditions. The protocol exhibited high regio- and stereoselectivity, favoring the exo-dig product with high Z selectivity. Moreover, the catalyst displayed excellent stability under the employed reaction conditions, as demonstrated by its good recyclability and low leaching.
Asunto(s)
Alquinos/química , Aminas/química , Lactonas/química , Paladio/química , Dióxido de Silicio/química , Catálisis , Ciclización , Estructura Molecular , EstereoisomerismoRESUMEN
A general and efficient route for the synthesis of enantiomerically pure α-substituted ketones and the corresponding lactones has been developed. Ruthenium- and enzyme-catalyzed dynamic kinetic resolution (DKR) with a subsequent Cu-catalyzed α-allylic substitution are the key steps of the route. The α-substituted ketones were obtained in high yields and with excellent enantiomeric excess. The methodology was applied to the synthesis of a naturally occurring caprolactone, (R)-10-methyl-6-undecanolide, via a subsequent Baeyer-Villiger oxidation.