Formation of Multiple Naturally Occurring Meroterpenoid Scaffolds by the Norrish-Yang Reaction of a p-Benzoquinone.

The Norrish-Yang reaction, as a typical example, demonstrates the inherent ability of photochemical reaction to facilitate formation of sterically congested C-C bonds, efficiently crafting intricate ring structure in complex organic molecules. Herein we report for the first time a unified synthesis using quinone-based acid-promoted Norrish-Yang photocyclization for the stereoselective construction of multiple avarane-type meroterpenoid natural products.

Stereoselective Construction of the ABCDE Pentacyclic Motif of Phainanoids via Norrish-Yang Photocyclization Reaction.

A Norrish-Yang photocyclization reaction has been applied to regio- and stereoselective construction of the ABCDE pentacyclic motif of natural product phainanoids. The observed substrate conformation control implicates this powerful reaction could be applied to the construction of structurally diverse natural product scaffolds.

From sky to road: Incorporating the satellite imagery into analysis of freight truck-related crash factors.

Freight truck-related crashes in urban contexts have caused significant economic losses and casualties, making it increasingly essential to understand the spatial patterns of such crashes. Limitations regarding data availability have greatly undermined the generalizability and applicability of certain prior research findings. This study explores the potential of emerging geospatial data to delve deeply into the determinants of these incidents with a more generalizable research design.

Exo-Selective Diels-Alder Reactions.

The Diels-Alder reaction stands as one of the most pivotal transformations in organic chemistry. Its efficiency, marked by the formation of two carbon-carbon bonds and up to four new stereocenters in a single step, underscores its versatility and indispensability in synthesizing natural products and pharmaceuticals. The most significant stereoselectivity feature is the "endo rule".

Exercise intervention for patients with chronic low back pain: a systematic review and network meta-analysis.

Purpose: Chronic low back pain (CLBP) is an aging and public health issue that is a leading cause of disability worldwide and has a significant economic impact on a global scale. Treatments for CLBP are varied, and there is currently no study with high-quality evidence to show which treatment works best. Exercise therapy has the characteristics of minor harm, low cost, and convenient implementation.

Synthesis of Polysubstituted Furans via Rh(II)-Catalyzed [2 + 3] Annulation of -Sulfonyl-1,2,3-triazoles with Enaminones.

An unprecedented [2 + 3] annulation of -sulfonyl-1,2,3-triazoles with enaminones is reported for the access of polysubstituted furans. The key to the success of the transformations lies in the use of Rh(II)-Brønsted acid as cooperative catalysts. Unlike the conventional annulations of -sulfony-l-1,2,3-triazoles, the Rh(II)-azavinyl carbenes species play dual functions in this work, enabled by the cleavage of the C(sp)N bond.

Synthesis towards Phainanoid F: Photo-induced 6π-Electrocyclization for Constructing Contiguous All-Carbon Quaternary Centers.

In this paper, we report an efficient strategy for synthesizing the DEFGH rings of phainanoid F. The key to the construction of the 13,30-cyclodammarane skeleton of the molecule was a photo-induced 6π-electrocyclization and a homoallylic elimination. Notably, this is a rare example of using electrocyclization reaction to simultaneously construct two vicinal quaternary carbons in total synthesis.

Highly Stereoselective Diels-Alder Reactions Catalyzed by Diboronate Complexes.

A highly enantioselective catalytic system for exo-Diels-Alder reactions was developed based on the newly discovered bispyrrolidine diboronates (BPDB). Activated by various Lewis or Brønsted acids, BPDB can catalyze highly stereoselective asymmetric exo-Diels-Alder reactions of monocarbonyl-based dienophiles. When 1,2-dicarbonyl-based dienophiles are used, the catalyst can sterically distinguish between the two binding sites, which leads to highly regioselective asymmetric Diels-Alder reactions.

Efficient acquisition of Mueller matrix via spatially modulated polarimetry at low light field.

Mueller polarimetry performed in low light field with high speed and accuracy is important for the diagnosis of living biological tissues. However, efficient acquisition of the Mueller matrix at low light field is challenging owing to the interference of background-noise. In this study, a spatially modulated Mueller polarimeter (SMMP) induced by a zero-order vortex quarter wave retarder is first presented to acquire the Mueller matrix rapidly using only four camera shots rather than 16 shots, as in the state of the art technique.

Mueller matrix imaging polarimeter at the wavelength of 265 nm.

Mueller matrix imaging polarimeters (MMIPs) have been developed in the wavelength region of >400 with great potential in many fields yet leaving a void of instrumentation and application in the ultraviolet (UV) region. For the first time to our knowledge, an UV-MMIP is developed for high resolution, sensitivity, and accuracy at the wavelength of 265 nm. A modified polarization state analyzer is designed and applied to suppress stray light for nice polarization images, and the errors of the measured Mueller matrices are calibrated to lower than 0.

Holistic and efficient calibration method for Mueller matrix imaging polarimeter with a high numerical aperture.

High-numerical aperture ( >0.6) Mueller matrix imaging polarimeter (MMIP) (high-NA MMIP) is urgently needed for higher resolution. Usually, the working distance of high-NA MMIP is too short to perform in situ calibration by a usual reference sample, such as polarizer and retarder plates.

Identification and semisynthesis of (-)-anisomelic acid as oral agent against SARS-CoV-2 in mice.

(-)-Anisomelic acid, isolated from (L.) Kuntze (Labiatae) leaves, is a macrocyclic cembranolide with a -fused α-methylene-γ-lactone motif. Anisomelic acid effectively inhibits SARS-CoV-2 replication and viral-induced cytopathic effects with an EC of 1.

Design of an extreme ultraviolet lithography projection objective with a grouping design method through forward and reverse real ray tracing.

As the logic node gets more and more advanced, the performance of extreme ultraviolet (EUV) objective projection is required to be higher and higher in a large field of view. It is known that a good initial structure can greatly reduce the dependence on the experience of optical designers. In this paper, a grouping design method through forward and reverse real ray tracing is proposed to design the aspheric initial structure for the EUV objective system.

Glutathione Is Involved in the Reduction of Methylarsenate to Generate Antibiotic Methylarsenite in Enterobacter sp. Strain CZ-1.

Methylarsenate (MAs(V)) is a product of microbial arsenic (As) biomethylation and has also been widely used as an herbicide. Some microbes are able to reduce nontoxic MAs(V) to highly toxic methylarsenite (MAs(III)) possibly as an antibiotic. The mechanism of MAs(V) reduction in microbes has not been elucidated.

Demethylation of the Antibiotic Methylarsenite is Coupled to Denitrification in Anoxic Paddy Soil.

Arsenic (As) biomethylation is an important component of the As biogeochemical cycle, which produces methylarsenite [MAs(III)] as an intermediate product. Its high toxicity is used by some microbes as an antibiotic to kill off other microbes and gain a competitive advantage. Some aerobic microbes have evolved a detoxification mechanism to demethylate MAs(III) via the dioxygenase C-As lyase ArsI.

Total Syntheses of Vicinal Dichloride Monoterpenes Enabled by Aza-Belluš-Claisen Rearrangement.

Diastereoselective syntheses of - and -vicinal dihalides were achieved via an aza-Belluš-Claisen rearrangement, which involved the reaction of an α-chloro carboxylic acid chloride with halogen-substituted -allyl morpholines in the presence of Lewis acids. The developed method was used for the total synthesis of a group of monoterpene natural products bearing vicinal dichloride subunits.

Tailored Synthesis of Skeletally Diverse Stemona Alkaloids through Chemoselective Dyotropic Rearrangements of β-Lactones.

The collective synthesis of skeletally diverse Stemona alkaloids featuring tailored dyotropic rearrangements of β-lactones as key elements is described. Specifically, three typical 5/7/5 tricyclic skeletons associated with stemoamide, tuberostemospiroline and parvistemonine were first accessed through chemoselective dyotropic rearrangements of β-lactones involving alkyl, hydrogen, and aryl migration, respectively. By the rational manipulation of substrate structures and reaction conditions, these dyotropic rearrangements proceeded with excellent efficiency, good chemoselectivity and high stereospecificity.

Stereoselective Synthesis of Cyclohepta[b]indoles by Visible-Light-Induced [2+2]-Cycloaddition/retro-Mannich-type Reactions.

A novel method for the concise synthesis of cyclohepta[b]indoles in high yields was developed. The method involves a visible-light-induced, photocatalyzed [2+2]-cycloaddition/ retro-Mannich-type reaction of enaminones. Experimental and computational studies suggested that the reaction is a photoredox process initiated by single-electron oxidation of an enaminone moiety, which undergoes subsequent cyclobutane formation and rapidly fragmentation in a radical-cation state to form cyclohepta[b]indoles.

Asymmetric Total Synthesis of (-)-Spirochensilide A, Part 2: The Final Phase and Completion.

The final phase of the total synthesis of (-)-spirochensilide A is described. A tungsten-mediated cyclopropene-based Pauson-Khand reaction was developed to form the spiral CD ring system with desired stereochemistry at the C13 quaternary center. Other important steps enabling completion of this synthesis included an intermolecular aldol condensation to link the ABCD core with the EF fragment and a Cu-mediated 1,4-addition to stereoselectively install the C21 stereogenic center.

Asymmetric Total Synthesis of (-)-Spirochensilide A, Part 1: Diastereoselective Synthesis of the ABCD Ring and Stereoselective Total Synthesis of 13()-Demethyl Spirochensilide A.

A concise and diastereoselective construction of the ABCD ring system of spirochensilide A is described. The key steps of this synthesis are a semipinacol rearrangement reaction to stereoselectively construct the AB ring system bearing two vicinal quaternary chiral centers and a Co-mediated Pauson-Khand reaction to form the spiro-based bicyclic CD ring system. This chemistry leads to the stereoselective synthesis of 13()-demethyl spirochensilide A, paving the way for the first asymmetric total synthesis of (-)-spirochensilide A.

Strain-Driven Dyotropic Rearrangement: A Unified Ring-Expansion Approach to α-Methylene-γ-butyrolactones.

An unprecedented strain-driven dyotropic rearrangement of α-methylene-β-lactones has been realized, which enables the efficient access of a wide range of α-methylene-γ-butyrolactones displaying remarkable structural diversity. Several appealing features of the reaction, including excellent efficiency, high stereospecificity, predictable chemoselectivity and broad substrate scope, render it a powerful tool for the synthesis of MBL-containing molecules of either natural or synthetic origin. Both experimental and computational evidences suggest that the new variant of dyotropic rearrangements proceed in a dualistic pattern: while an asynchronous concerted mechanism most likely accounts for the reactions featuring hydrogen migration, a stepwise process involving a phenonium ion intermediate is favored in the cases of aryl migration.

Photoredox-Catalyzed Isomerization of Highly Substituted Allylic Alcohols by C-H Bond Activation.

Photoredox-catalyzed isomerization of γ-carbonyl-substituted allylic alcohols to their corresponding carbonyl compounds was achieved for the first time by C-H bond activation. This catalytic redox-neutral process resulted in the synthesis of 1,4-dicarbonyl compounds. Notably, allylic alcohols bearing tetrasubstituted olefins can also be transformed into their corresponding carbonyl compounds.

Asymmetric Total Synthesis of (-)-Pavidolide B via a Thiyl-Radical-Mediated [3 + 2] Annulation Reaction.

The development of an efficient strategy for the asymmetric total synthesis of the bioactive marine natural product (-)-pavidolide B is described in detail. The development process and detours leading to the key thiyl-radical-mediated [3 + 2] annulation reaction, which constructed the central C ring with four contiguous stereogenic centers in one step, are depicted. Subsequently, the seven-membered D ring is constructed via a ring-closing metathesis reaction followed by a Rh(III)-catalyzed isomerization.

Total Syntheses of Asperchalasines A-E.

The first total syntheses of asperchalasines A-E, a collection of unprecedented merocytochalasans, are reported. Aspochalasin B, a key tricyclic cytochalasan monomer, was first synthesized through a unified approach that hinges on a Diels-Alder reaction and a ring-closing metathesis reaction. The bioinspired Diels-Alder reactions of aspochalasin B with different epicoccine precursors were then explored, which enabled the divergent access of the heterodimers asperchalasines B-E as well as related congeners.

Nature-Inspired Bioorthogonal Reaction: Development of β-Caryophyllene as a Chemical Reporter in Tetrazine Ligation.

A nature-inspired bioorthogonal reaction has been developed, hinging on an inverse-electron-demand Diels-Alder reaction of tetrazine with β-caryophyllene. Readily accessible from the cheap starting material through a scalable synthesis, the newly developed β-caryophyllene chemical reporter displays appealing reaction kinetics and excellent biocompatibility, which renders it applicable to both in vitro protein labeling and live cell imaging. Moreover, it can be used orthogonally to the strain-promoted alkyne-azide cycloaddition for dual protein labeling.