RESUMO
Under the catalysis of simple Lewis acid catalysts, 2-(1-aroylcyclopropyl)malonates demonstrated unique reactivities in annulation reactions with aryl/alkyl aldehydes, paraformaldehyde, and 1,3,5-triazinanes. Three types of structurally diverse cyclic products that are otherwise not easy to obtain were generated in moderate to good yields and excellent diastereoselectivities. Possible reaction pathways leading to these products were proposed on the basis of the results of control experiments.
RESUMO
As a type of readily available small strained-ring heterocycle, meso-aziridines may undergo catalytic desymmetrizing transformations to empower the rapid construction of diverse nitrogen-containing structures bearing contiguous stereocenters, which have great relevance in natural product synthesis, drug development and the design and synthesis of chiral catalysts/ligands for asymmetric catalysis. This review outlines the advances achieved in the catalytic asymmetric desymmetrization of meso aziridines and highlights some promising avenues for further work in this realm.
Assuntos
Aziridinas , Estereoisomerismo , Aziridinas/química , Catálise , LigantesRESUMO
Herein, we synthesized and characterized a binuclear copper(I) complex supported by the indolyl-based ligand. Employing this complex as catalyst, we have developed a three-component intermolecular trifluoromethylazolation of alkenes to deliver various trifluoromethylated azole derivatives. The method features exclusive chemo- and regioselectivity, a broad scope of alkenes and oxazoles, thiazoles, and good tolerance of functional groups under mild conditions. Preliminary mechanistic studies support a radical process for the transformation.
RESUMO
A tandem insertion of aliphatic nitriles and unactivated alkenes to the N-H bond of secondary aliphatic amines catalyzed by simple trialkyl rare-earth metal complexes was disclosed. This reaction provides a highly atom-economic and stereoselective way to a range of cyclic amidines under mild reaction conditions.
Assuntos
Aminas , Elementos da Série dos Lantanídeos , Alcenos , Amidinas , CatáliseRESUMO
Hantzsch esters (HEs) served as two-carbon partners in a copper(I)-catalyzed enantioselective [3 + 2] annulation with racemic 2-(hetero)aryl-N-sulfonyl aziridines via kinetic resolution to provide pyrrolo[2,3-b]tetrahydropyridines containing multiple contiguous stereogenic centers including all-carbon quaternary centers in excellent yields and enantiopurities and moderate-to-excellent diastereoselectivities. Mainly dependent upon the structures of the aziridines, a competitive hydrogenolysis process with HEs as the hydrogen source was also observed in some cases.
RESUMO
The Lewis acid-catalyzed annulations between anthranils and γ-butyrolactone-fused donor-acceptor cyclopropanes have been developed. Depending on the anthranils used, such annulations proceeded in a chemodivergent way to produce either bridged cyclic products via [4 + 3] annulation or γ-butyrolactone-fused tetrahydroquinoline products via a cascade process in moderate to high yields. A probable mechanism for the two reaction pathways has been proposed. The reaction could be performed on a gram-scale, and the products could be elaborated to other useful cyclic structures bearing multiple contiguous stereogenic centers.
RESUMO
The synthesis of 2-aminophosphates is achieved by a SN2-type ring opening reaction of various N-protected or free aziridines with phosphoric acids in a regiospecific and/or enantiospecific way. A one-pot, two-step procedure is also developed enabling direct access to 2-aminophosphates from olefins without isolation of the aziridine intermediates.
RESUMO
The first Lewis acid catalyzed stereoconvergent transformation of racemic 2-(hetero)aryl- N-sulfonylaziridines via C-N bond cleavage with nucleophiles is presented. This includes the [3 + 2] annulations with (hetero)aromatic aldehydes and 1,3-disubstituted indoles, asymmetric Friedel-Crafts type reaction with electron-rich (hetero)arenes, and asymmetric aminolysis with amines, providing facile access to chiral 1,3-isoxazolidines, pyrroloindolines, 2-(hetero)arylphenethylamines, and vicinal diamines. This method features a simple and cheaply available complex of Cu(I)-chiral BINAP catalyst, excellent yield and high diastereo- and enantioselectivities, and mild reaction conditions. A mechanism involving type I dynamic kinetic asymmetric transformations (DyKATs) of the racemic aziridines is proposed based on the results of control experiments.
RESUMO
A new Michael addition/intramolecular alkylation sequence of ( Z)-3-(2-bromo-3-arylacryloyl)oxazolidin-2-ones and malonates was developed. By a simple switch of the reaction conditions including the base promoter, solvent, and reaction temperature, both of the cis- and trans-isomers of a series of oxazolidinone-containing 2,3-disubstituted cyclopropane-1,1-diesters could be obtained in good-to-excellent yields and with an excellent diastereoselectivity. The utility of the cyclopropane products was demonstrated in the diastereoselective syntheses of (±)-urinaligran and a stereoisomer of (±)-virgatusin involving the AlCl3-promoted [3+2] annulation with veraldehyde or piperonal as the key step.
RESUMO
An enantiospecific [3 + 2] annulation of γ-butyrolactone fused cyclopropanes with aromatic aldehydes was realized under Lewis acid catalysis. This method provides facile access to a series of chiral furanolignan derivatives bearing multiple contiguous stereogenic centers in good-to-excellent yields, exclusive diastereoselectivities and excellent enantiopurities under mild reaction conditions. Elaboration work on the product of this reaction delivers stereoisomeric analogues of (+)-virgatusin and suggests a structural revision might be necessary for a previously reported isolated natural product.
RESUMO
The [3 + 2] annulations of γ-butyrolactone fused donor-acceptor (D-A) cyclopropanes with aromatic isothiocyanates and dialkyl carbodiimides promoted by FeCl3 is reported. A series of bicyclic/polycyclic γ-butyrolactone fused thioimidates and γ-butyrolactone fused amidines containing four contiguous stereogenic centers were obtained in excellent yields as single stereoisomers.
RESUMO
The kinetic resolution of 2-aryl-N-tosylaziridines and the asymmetric desymmetrization of meso-N-tosylaziridines by ring openings with various primary and secondary anilines, and aliphatic amines as nucleophile have been realized by using a single silver(I)/chiral diphosphine complex as catalyst for the first time. The simple starting materials, broad scope, and easy scalability render this protocol a practical way to chiral vicinal diamine derivatives.
RESUMO
Over the past few decades, enantioselective phosphine organocatalysis has evolved rapidly into a highly efficient catalytic strategy for a range of useful reactions. However, as restricted by the traditional catalytic modes, some important reactions, such as asymmetric Strecker-type reactions, have thus far been out of reach of this strategy. Reported herein is an application of enantioselective phosphine organocatalysis for asymmetric Strecker-type reactions, enabled by a dual-reagent catalyst system in which the key organophosphorus zwitterion intermediate, generated in situ by mixing a chiral dipeptide-derived multifunctional organophosphine with methyl acrylate, is used as a highly efficient chiral Lewis base catalyst. The high efficiency of this catalytic system is demonstrated in the asymmetric cyanation of isatin-derived ketimines and azomethine aldimines as well as in the kinetic resolution of racemic 3-substituted azomethines. Mechanistic studies provide experimental evidence for the intermediacy of the putative zwitterion and its role as a catalytically active Lewis base.
RESUMO
A highly enantioselective α-amination of 3-substituted oxindoles with azodicarboxylates catalyzed by amino acids-derived chiral phosphine catalysts is reported. The corresponding products containing a tetrasubstituted carbon center attached to a nitrogen atom at the C-3 position of the oxindole were obtained in high yields and with up to 98% ee.
RESUMO
An organocatalytic dearomative [3 + 2]-annulation of N-alkyl-3-alkylindoles with quinone monoketals is developed. The reaction provides a mild and straightforward way to various benzofuro[2,3-b]indolines of potential biological and pharmaceutical interest in moderate to good yields. Moreover, when 3-phenylindole, a problematic substrate in previous relevant studies, was used as the substrate under the otherwise same reaction conditions, a novel 1,2-shift of the phenyl group occurred followed by aromatization to provide 2,3-diaryl indoles useful for cancer therapy studies in moderate yields.
Assuntos
Ácidos/química , Benzoquinonas/química , Indóis/química , Indóis/síntese química , Catálise , Ciclização , Modelos Moleculares , Estrutura MolecularRESUMO
The first Lewis acid catalyzed [3 + 2] annulation of indoles and 2-aryl-N-tosylaziridines was realized by using copper(I)/chiral diphosphine complexes as a catalyst. With this method, a variety of uniquely substituted chiral pyrroloindolines bearing multiple contiguous stereogenic centers were facilely accessed in a straightforward, high-yielding, and highly stereoselective way under mild conditions.
RESUMO
The combination of a new bifunctional phosphine and an acrylate generate a zwitterion inâ situ and it serves as an efficient catalyst for asymmetric reactions through a homogeneous ion-pairing mode. This new catalytic system has been successfully applied to Mannich-type reactions to give excellent results and it demonstrates a broad substrate scope. Such reactivity is not accessible with general organophosphine catalytic modes. Preliminary investigations into the mechanism are also presented.
RESUMO
A novel Lewis acid catalyzed dehydrative [3 + 3]-annulation of readily available benzylic alcohols and propargylic alcohols was developed to give polysubstituted carbazoles and naphthalenes in moderate to good yields with water as the only byproduct. The reaction was presumed to proceed via a cascade process involving Friedel-Crafts-type allenylation, 1,5-hydride shift, 6π-eletrocyclization, and Wagner-Meerwein rearrangement.
Assuntos
Alcinos/química , Carbazóis/síntese química , Ácidos de Lewis/química , Naftalenos/síntese química , Propanóis/química , Álcool Benzílico/química , Carbazóis/química , Catálise , Estrutura Molecular , Naftalenos/química , Estereoisomerismo , ÁguaRESUMO
Polysubstituted pyrroles were regioselectively synthesized in moderate to good yields via the copper acetate-catalyzed [3 + 2] annulation reaction of readily accessible aziridines and nitroalkenes. This reaction was proposed to proceed through a key azomethine ylide intermediate generated by selective C-C bond cleavage of the aziridine followed by annulation with nitroalkenes under aerobic conditions.
Assuntos
Alcenos/química , Aziridinas/química , Nitrocompostos/química , Pirróis/síntese química , Catálise , Cobre/química , Pirróis/química , EstereoisomerismoRESUMO
A new chiral silicon-linked tridentate amido-indenyl ligand was developed from indene and enantiopure 1,2-cyclohexanediamine. Its yttrium complex was synthesized, characterized and applied to efficiently catalyze the intramolecular hydroamination of non-activated olefins with up to 97% ee.