Polarizability matters in enantio-selection.

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.

Visible-Light-Promoted Photoredox Syntheses of α,ß-Epoxy Ketones from Styrenes and Benzaldehydes under Alkaline Conditions.

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.

Visible-Light-Promoted Vinylation of Tetrahydrofuran with Alkynes through Direct C-H Bond Functionalization.

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.

Gold-catalyzed rearrangement of alkynyl donor-acceptor cyclopropanes to construct highly functionalized alkylidenecyclopentenes.

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.

N,N-Dimethylaminobenzoates enable highly enantioselective Sharpless dihydroxylations of 1,1-disubstituted alkenes.

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.

Gold catalysis coupled with visible light stimulation: syntheses of functionalized indoles.

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.

Asymmetric synthesis of the tricyclic core of Calyciphylline A-type alkaloids via intramolecular [3 + 2] cycloaddition.

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.

Structural Insights on the bacteriolytic and self-protection mechanism of muramidase effector Tse3 in Pseudomonas aeruginosa.

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.

Ortho-dearomatization of phenols creating all-carbon spiro-bicycles.

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.

Ag-carbenoid-initiated catalytic hydration cascades: rapid construction of functionalized bicyclo[3.3.1]nonanes.

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.

New approach to oximes through reduction of nitro compounds enabled by visible light photoredox catalysis.

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.

Tackling reactivity and selectivity within a strained architecture: construction of the [6-6-5-7] tetracyclic core of Calyciphylline alkaloids.

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.

Rapid construction of [5-6-7] tricyclic ring skeleton of Calyciphylline alkaloid daphnilongeranin B.

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.

Biomimetic total syntheses of linderaspirone A and bi-linderone and revisions of their biosynthetic pathways.

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.

Enantioselective organocatalytic mannich reactions with autocatalysts and their mimics.

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.

A model study for the concise construction of the oxapentacyclic core of cortistatins through intramolecular Diels-Alder and oxidative dearomatization-cyclization reactions.

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.

Diversity-oriented synthesis of fused pyran gamma-lactones via an efficient Pd-thiourea-catalyzed alkoxycarbonylative annulation.

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.

A [5]HELOL analogue that senses remote chirality in alcohols, phenols, amines, and carboxylic acids.

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.