RESUMEN
A new organocatalytic approach for the synthesis of a variety of α-alkyl, α-phenylselenyl ketones as well as their corresponding esters and amides, by the addition of α-selenocarbonyl derivatives to nitroalkenes catalyzed by thiourea or squaramide cinchona catalysts, is presented. This catalytic system allows the preparation in high yields of enantiomerically enriched selenocarbonyl derivatives bearing two chiral centers with excellent ee's and dr's by using catalytic loadings of 3 mol%.
Asunto(s)
Amidas/síntesis química , Cetonas/síntesis química , Compuestos de Organoselenio/síntesis química , Amidas/química , Catálisis , Cinchona/química , Técnicas Químicas Combinatorias , Ésteres , Cetonas/química , Estructura Molecular , Compuestos de Organoselenio/química , Estereoisomerismo , Tiourea/químicaRESUMEN
The reactions of readily available vinyl selenones with enantiopure 1,2-diols, N-protected-1,2-aminoalcohols, and diamines gave substituted enantiopure 1,4-dioxanes, morpholines, and piperazines, respectively, in good to excellent yields. The same procedure was extended to the synthesis of thiomorpholine, benzodiazepine, and benzoxazepine. The reactions proceeded in one pot, in the presence of base, through a simple and novel application of the Michael-initiated, ring-closure (MIRC) reactions. The formed heterocycles constitute a framework that is observed in a large number of pharmaceutical compounds.
Asunto(s)
Amino Alcoholes/química , Diaminas/química , Dioxanos/síntesis química , Morfolinas/síntesis química , Piperazinas/síntesis química , Compuestos de Vinilo/química , Dioxanos/química , Estructura Molecular , Morfolinas/química , Piperazinas/química , EstereoisomerismoRESUMEN
The reaction of readily available (5R)-5-but-3-en-1-ylpyrrolidin-2-one with aryl bromides, chlorides, or triflates in the presence of Pd(2)(dba)(3), Xphos, and Cs(2)CO(3) in 1,4-dioxane at 120 degrees C affords (5R,7aR)-5-aryl hexahydropyrrolizidin-3-ones in good to high yields through a diastereoselective carboamination reaction. Aryl iodides are less successful substrates than bromides and chlorides.
Asunto(s)
Paladio/química , Pirrolidinas/síntesis química , Pirrolidinonas/síntesis química , Aminación , Catálisis , Pirrolidinas/química , Pirrolidinonas/química , EstereoisomerismoRESUMEN
A stereospecific synthesis of beta(3)-amino acids has been accomplished starting from readily available and enantioenriched propargylic alcohols. This conversion can be effected in only three steps by selenium-mediated organic transformations of the carbon-carbon triple bond. This method is especially attractive because the reactive Se-phenyl selenocarboxylate intermediates can be trapped with the amine functionality of an amino acid derivative. Through this strategy a chain elongation at the N-terminus has been effected. The N-deprotection and repetition of the homologation with other Se-phenyl selenocarboxylate intermediates produced beta- and mixed alpha/beta-oligopeptides without the use of coupling agents.
Asunto(s)
Alquinos/química , Aminoácidos/síntesis química , Oligopéptidos/síntesis química , Compuestos Organometálicos/síntesis química , Propanoles/química , Selenio/química , Aminoácidos/química , Técnicas Químicas Combinatorias , Estructura Molecular , Oligopéptidos/química , Compuestos Organometálicos/química , EstereoisomerismoRESUMEN
Different synthetic methodologies for the stereocontrolled synthesis of substituted azetidines are reported. The approach utilizes an optimized oxidation reaction of gamma-(phenylseleno)alkyl arylsulfonamides, followed by the intramolecular substitution of the resulting phenylselenonyl group by the nitrogen atom.
Asunto(s)
Aminas/química , Azetidinas/síntesis química , Compuestos de Organoselenio/química , Sulfonamidas/química , Azetidinas/química , Estructura Molecular , EstereoisomerismoRESUMEN
[reaction: see text] The first example of a kinetic resolution process promoted by electrophilic selenium reagents is reported. Racemic allylic alcohols react with half equivalents of a selenenylating agent in methanol leading to the regiospecific formation of the corresponding addition products with a very high level of facial selectivity (from 95:5 to 98:2 dr). The unreacted alcohols can be recovered in an optically enriched form (from 90 to 94% ee).
RESUMEN
A new and convenient method for the stereospecific synthesis of variously substituted 1,3-oxazolidin-2-ones from the easily available beta-hydroxyalkyl phenyl selenides is presented. After transformation into the N-tosyl or N-benzoyl carbamates, the selenides were oxidized to the corresponding selenones. The key step of the process is the ring-closure reaction, which occurs by stereospecific intramolecular nucleophilic substitution of the selenone group by the nitrogen atom of the carbamate. Enantiomerically pure 1,3-oxazolidin-2-one derivatives can be easily prepared by using enantiomerically pure beta-hydroxyalkyl phenyl selenides as starting materials.
Asunto(s)
Nitrógeno/química , Compuestos de Organoselenio , Oxazolidinonas/síntesis química , Ciclización , Conformación Molecular , Compuestos de Organoselenio/síntesis química , Compuestos de Organoselenio/química , EstereoisomerismoRESUMEN
The synthesis of the new chiral non-racemic sulfur-containing diselenide, di-2-methoxy-6-[(1S)-1-(methylthio)ethyl]phenyl diselenide, is described. When treated with ammonium persulfate this diselenide is transformed into the corresponding selenenyl sulfate, which acts as a strong electrophilic reagent and adds to alkenes, in the presence of methanol or water, to afford the products of selenomethoxylation or selenohydroxylation, respectively, with excellent diastereoselectivities. Starting from alkenes containing internal nucleophiles, asymmetric cyclofunctionalization reactions also resulted in good chemical yields, complete regioselectivities, and high diastereoselectivities. This sulfur-containing diselenide can also be used in catalytic amounts to promote one-pot selenenylation-deselenenylation processes, from which several types of products can be obtained in high yield and with good enantiomeric excess.
RESUMEN
After activation with electrophilic selenenylating agents, the phenylseleno group of vicinal azido selenides, containing internal oxygen or nitrogen nucleophilic substituents, readily undergoes intramolecular nucleophilic displacement to afford azido-substituted heterocyclic compounds. This intramolecular substitution occurs with inversion of configuration at the carbon atom bearing the selenium atom. Starting from acetamido selenides and carbamato selenides, a stereocontrolled synthesis of the vicinal amino alcohol precursor oxazolines and oxazolidin-2-ones has been developed.