RESUMO
On the basis of a novel umpolung strategy, an efficient l-amino acid ester-mediated in situ reduction of 2-(2-oxoindolin-3-ylidene)malononitrile and sequential nucleophilic addition/cyclization cascade reaction is reported. Various densely substituted cyclopentene bispirooxindoles and dihydrofuran bispirooxindoles with two quaternary spirocenters were constructed in high yields (≤93%) with excellent diastereoselectivities (>20:1 dr). The method has advantages of readily available starting materials, mild reaction conditions, a one-pot process, a metal-free biomimetic reducing agent, a wide substrate scope, and operational simplicity (single filtration without column chromatography).
RESUMO
One-pot ring-opening/ring-closure process of combining methyleneindolinone with 3-aminooxindole has been developed in this work. Novel polycyclic spirooxindoles were efficiently assembled under mild conditions in high yields (up to 95 %) with moderate to good diastereoselectivities (up to >95:5â d.r.) through simple filtration.
RESUMO
Hydrogen-bonding organocatalysts L-pyroglutamic sulphonamides were readily synthesized for the first time by fully exploiting the potentials of L-pyroglutamic acid. The newly designed catalyst was successfully applied in catalyzing asymmetric Diels-Alder cyclization of methyleneindolinones with 2-vinyl-1H-indoles to efficiently assemble carbazolespirooxindoles in excellent stereoselectivity (up to 99% ee, >20:1 dr) and yields (up to 99%). Mechanistic studies disclosed that the well-designed hydrogen-bonding modes between L-pyroglutamic sulphonamide and substrates were crucial for stereocontrol in the cyclization.
RESUMO
A series of novel dispirooxindole derivatives, 3-acetyl-5-phenyl-pyrrolo(spiro-[2.3']-1'-benzyl-oxindole)-spiro-[4.3"]-1"-benzyl-oxindoles, were synthesized via 1,3-dipolar cycloaddition of the azomethine ylide with 3-acetonylideneoxindole in high regioselectivities and yields. An unusual regioselectivity was observed in this 1,3-dipolar cycloaddition, leading to the construction of novel dispirooxindole skeleton. The substituent effects on the regioselectivity were also investigated.
Assuntos
Compostos Azo/química , Indóis/química , Indóis/síntese química , Pirróis/síntese química , Tiossemicarbazonas/química , Ciclização , Estrutura Molecular , Oxindóis , Pirróis/químicaRESUMO
An efficient triphenylphosphine oxide-catalyzed amidation and esterification for the rapid synthesis of a series of dipeptides, amides, and esters is described. This reaction is applicable to challenging couplings of hindered carboxylic acids with weakly nucleophilic amines or alcohols, giving the products in good yields (67-90%) without racemization. This system employs the highly reactive intermediate Ph3PCl2 as the activator of the carboxylate in a catalytic manner and drives the reaction to completion in a short reaction time (less than 10 min).
RESUMO
A one-pot squaramide-catalyzed enantioselective ring-reorganization domino sequence (Michael addition/intramolecular ring-opening/lactamization) of 3-hydroxyoxindole and methyleneindolinone, which can be readily derived from 3-oxindole, has been established in this work. As a result, novel polycyclic quinolinone-spirooxindoles bearing three contiguous chiral centers were efficiently and step-economically assembled under mild conditions in high yields (up to 97%) with excellent enantioselectivities (up to >99% ee) and moderate to good diastereoselectivities (up to >95:5 dr).
RESUMO
A visible-light-induced difluoroalkylation of N,N'-cyclicazomethine imine was successfully realized through a novel photoredox radical-radical cross-coupling reaction. This developed protocol exhibits high functional group tolerance and affords a variety of difluorinated 3-pyrazolidinone scaffolds. Extensive mechanistic investigations have been undertaken, well revealing the involvement of a reductive radical-radical coupling pathway.