RESUMO
The prevalence of chirality, or, handedness in biological world is a fundamental phenomenon and a characteristic hallmark of life. Thus, understanding the origin of enantio-selection, i.e., the sense and magnitude of asymmetric induction, has been a long-pursued goal in asymmetric catalysis. Herein, we demonstrated a polarizability-derived electronic effect that was shown to be capable of rationalizing a broad range of stereochemical observations made in the field of asymmetric catalysis. This effect provided a consistent enantio-control model for the prediction of major enantiomers formed in a ruthenium-catalyzed asymmetric transfer hydrogenations of ketones. Direct and quantitative linear free energy relationships between substrates' local polarizabilities and observed enantio-selectivity were also revealed in three widely known asymmetric catalytic systems covering both reductions and oxidations. This broadly applicable polarizability-based electronic effect, in conjunction with conventional wisdom mainly leveraging on steric effect considerations, should aid rational design of enantio-selective processes for better production of chiral substances.
RESUMO
A range of styrenes and benzaldehydes were smoothly combined to form α,ß-epoxy ketones under the synergistic actions of photocatalyst Ru(bpy)3Cl2, tert-butyl hydroperoxide (t-BuOOH), cesium carbonate (Cs2CO3), and visible light irradiation. The process likely proceeds through visible-light-enabled photocatalytic generations of acyl radicals as key intermediates.
RESUMO
A gold-catalyzed 1,7-addition-cyclization-elimination cascade sequence performed on a range of alkynyl-substituted donor-acceptor-type cyclopropanes provides facile entry to highly functionalized exo-alkylidenecyclopentenes under very mild conditions. Isolation of the relevant allyl ether intermediate helped shed light on the reaction's mechanistic course.
RESUMO
Mild and direct C-H bond functionalizations and vinylations of tetrahydrofuran with alkynes have been accomplished through visible light photocatalysis, yielding a range of vinyl tetrahydrofurans under the synergistic actions of organic dye-type photocatalyst eosin Y, tert-butyl hydroperoxide (t-BuOOH), and a 45 W household lightbulb. A significant kinetic isotope effect (KIE) was recorded, which helps shed light on the mechanistic course.
RESUMO
A judicious combination of Au-catalysis and synergistic visible-light stimulation formulates an exceptionally simple and mild reaction system capable of directly coupling anilines and alkynes to form multifunctionalized indoles.
Assuntos
Alcinos/química , Compostos de Anilina/química , Ouro/química , Indóis/síntese química , Catálise , Ciclização , Indóis/química , Luz , Estrutura MolecularRESUMO
A design scenario aimed at exploring beneficial catalyst-substrate π-π stacking electronic interactions in the classical Sharpless asymmetric dihydroxylations (SAD) leads to the identification of highly polarizable allylic N,N-dimethylaminobenzoate as a remarkably efficient auxiliary for inducing high levels of enantioselectivities (up to 99% ee) in the traditionally challenging substrate class of 1,1-disubstituted aliphatic alkenes.
Assuntos
Alcenos/química , p-Dimetilaminoazobenzeno/química , Catálise , Hidroxilação , EstereoisomerismoRESUMO
Asymmetric synthesis of the [5-6-7] tricyclic system common to the Calyciphylline A-type alkaloids is reported, featuring Overman rearrangement, Heck cyclization, intramolecular [3 + 2] cycloaddition, diastereoselective hydrogenation, and Claisen rearrangement as strategic events. The approach is capable of installing the crucial carbonyl functionality as well as multiple stereogenic centers within a congested polycyclic ring skeleton.
Assuntos
Alcaloides/síntese química , Compostos Policíclicos/síntese química , Alcaloides/química , Ciclização , Reação de Cicloadição , Hidrogenação , Estrutura Molecular , Compostos Policíclicos/química , Saxifragaceae/química , EstereoisomerismoRESUMO
The warfare among microbial species as well as between pathogens and hosts is fierce, complicated, and continuous. In Pseudomonas aeruginosa, the muramidase effector Tse3 (Type VI secretion exported 3) can be injected into the periplasm of neighboring bacterial competitors by a Type VI secretion apparatus, eventually leading to cell lysis and death. However, P. aeruginosa protects itself from lysis by expressing immune protein Tsi3 (Type six secretion immunity 3). Here, we report the crystal structure of the Tse3-Tsi3 complex at 1.8 Å resolution, revealing that Tse3 possesses one open accessible, goose-type lysozyme-like domain with peptidoglycan hydrolysis activity. Calcium ions bind specifically in the Tse3 active site and are identified to be crucial for its bacteriolytic activity. In combination with biochemical studies, the structural basis of self-protection mechanism of Tsi3 is also elucidated, thus providing an understanding and new insights into the effectors of Type VI secretion system.
Assuntos
Sistemas de Secreção Bacterianos/fisiologia , Cálcio/química , Proteínas Periplásmicas/química , Pseudomonas aeruginosa/química , Cálcio/metabolismo , Cristalografia por Raios X , Proteínas Periplásmicas/metabolismo , Estrutura Terciária de Proteína , Pseudomonas aeruginosa/metabolismo , Relação Estrutura-AtividadeRESUMO
A range of alkene-linked phenols are generally and reliably dearomatized specifically at their ortho-positions to create all-carbon quaternary stereogenic centers at the corresponding spiro-ring junctions, thus establishing a viable solution to the long-standing synthetic challenge.
Assuntos
Fenóis/química , Compostos de Espiro/química , Compostos de Espiro/síntese química , Catálise , Estrutura Molecular , EstereoisomerismoRESUMO
Remarkable Ag-carbenoid-initiated enone cyclopropanation-hydrolytic fragmentation-competitive 1,2-vs-1,4 addition reaction cascades were uncovered on a range of propargylic esters tethered to cyclohexadienones, leading to the highly efficient and stereospecific construction of densely functionalized bicyclo[3.3.1]nonanes under mild conditions.
Assuntos
Compostos Bicíclicos com Pontes/química , Ciclopropanos/química , Prata/química , Catálise , Estrutura Molecular , EstereoisomerismoRESUMO
A range of nitro compounds are smoothly reduced to their corresponding oximes under the synergistic effects of visible light irradiation, the Ru(bpy)3Cl2 photocatalyst, Hünig's base, Mg(ClO4)2 activation, and MeCN solvent. This remarkably mild and environmentally benign protocol, when orchestrated with classical Beckmann rearrangement, enables such high-value industrial feedstock as caprolactam to be readily accessed from simple precursor nitrocyclohexane.
Assuntos
Complexos de Coordenação/química , Nitrocompostos/química , Oximas/síntese química , Catálise , Luz , Compostos de Magnésio/química , Estrutura Molecular , Oxirredução , Oximas/química , Percloratos/química , Processos Fotoquímicos , Rutênio/químicaRESUMO
A stereochemically controlled route to the enantiopure [6-6-5-7] tetracyclic core of Calyciphylline A class alkaloids was established, which involves Overman rearrangement, [2 + 2] photochemical cycloaddition, Grob fragmentation, C-N bond-forming nucleophilic displacement, and ring strain-directed hydrogenation as strategic steps.
Assuntos
Compostos Policíclicos/síntese química , Ciclização , Conformação Molecular , Processos Fotoquímicos , Compostos Policíclicos/químicaRESUMO
A concise photochemical [2 + 2] cycloaddition-Grob fragmentation sequence sets the common tricyclic ring skeletons of the Calyciphylline A-type alkaloids, particularly those in daphnilongeranins, daphniyunnines, and daphniglaucins.
Assuntos
Alcaloides/síntese química , Ciclização , Estrutura Molecular , Fatores de TempoRESUMO
Simple exposure to sunlight is sufficient for triggering photochemical [2 + 2] cycloaddition-Cope or radical rearrangement cascades in the naturally occurring methyl linderone, leading to efficient biomimetic total syntheses of linderaspirone A and bi-linderone, two recently discovered bioactive spirocyclopentenedione natural products.
Assuntos
Materiais Biomiméticos/síntese química , Lactonas/síntese química , Compostos de Espiro/síntese química , Dimerização , Modelos Moleculares , Estrutura MolecularRESUMO
The Mannich reactions previously extensively investigated with organocatalysis of l-proline and other related small molecules were reinvestigated with detailed stereochemical analysis of their autocatalysis pathways, through employment of both the products themselves and their close structural mimics as the catalysts. These organo-autocatalytic processes function as meaningful molecular models toward understanding the origin and maintenance of homochirality under biologically relevant conditions.
Assuntos
Compostos Organometálicos/química , Prolina/química , Zinco/química , Catálise , Cromatografia Líquida de Alta Pressão , Espectroscopia de Ressonância Magnética , Modelos Químicos , Modelos Moleculares , Estrutura Molecular , EstereoisomerismoRESUMO
A unified strategy towards the facile construction of the [6.7.6.5] oxapentacyclic skeleton of cortistatins is reported, featuring intramolecular Diels-Alder (IMDA) and oxidative dearomatization-cyclization reactions as key steps.
Assuntos
Modelos Químicos , Neuropeptídeos/síntese química , Animais , Ciclização , Humanos , Neuropeptídeos/química , OxirreduçãoRESUMO
We reported herein a diversity-oriented synthesis of a range of fused pyran-gamma-lactones that was effected through a versatile Pd-thiourea complex-catalyzed intramolecular alkoxycarbonylative annulation.
Assuntos
Álcoois/química , Cetonas/química , Lactonas/síntese química , Paládio/química , Piranos/química , Tioureia/química , Catálise , Lactonas/químicaRESUMO
A route is developed to a structural analogue of [5]HELOL, a previously reported helically grooved sensor of remote chirality. It gives the material enantiomerically pure and in multigram quantities. The enantiomers of alcohols, phenols, amines, and carboxylic acids, even when their centers of chirality are remote from any functional groups, can be differentiated by 31P NMR spectroscopic analyses of their reaction products with the chlorophosphite of this material.