Divergent Coupling of ortho-Alkynylnaphthols and Benzofurans: [4 + 2] Cycloaddition and Friedel-Crafts Reaction.

Catalytic direct [4 + 2] cycloaddition reactions and Friedel-Crafts reactions of ortho-alkynylnaphthols with benzofurans have been developed, affording functionalized hydrobenzofuro[3,2-b]chromans and hydroarylation products, respectively, in high yields with high chemoselectivity.

Cu(OTf)2-Phosphoric Acid-Catalyzed Tandem Oxa-Nazarov Cyclization and Dibromination of Conjugated 1,2-Diketones.

A facile tandem oxa-Nazarov cyclization and dibromination has been developed. The combination of Cu(OTf)2 and diphenyl phosphate (DPP-H) was found to synergistically promote the coupling of conjugated 1,2-diketones and N-bromosuccinimide to form 2,4-dibromo-3(2H)-furanones in good yields.

Construction of Axially Chiral Styrenes Linking an Indole Moiety by Chiral Phosphoric Acid.

Herein we report a chiral phosphoric acid-catalyzed intermolecular C2 Friedel-Crafts alkylation reaction between ortho-alkynylnaphthols and various 3-substituted indoles, affording axially chiral alkenes with up to 93% yields (E/Z > 20:1) and up to 98% ee under mild reaction condition. Other substituted indole derivatives could be also tolerated in this system, giving the corresponding axially chiral alkenes with high yields and in excellent enantioselectivity.

Enantioselective Friedel-Crafts Reaction of 2-Alkynyphenols with Aromatic Ethers by Chiral Brønsted Acid Catalysis.

Herein, we report chiral strong Brønsted acid-catalyzed enantioselective Friedel-Crafts reaction of 2-alkynyphenols with aromatic ethers. The reaction affords the corresponding axially chiral styrenes in up to 91% yield and 97% ee.

HfCl4-Catalyzed [4 + 2] Cycloaddition of ß,γ-Unsaturated α-Keto Esters with Alkynes.

Herein we report Lewis acid HfCl4-catalyzed [4 + 2] cycloaddition between ß,γ-unsaturated α-keto esters and various symmetric or unsymmetric alkynes, giving the desired polysubstituted 4H-pyrans in up to 98% yield and with excellent regioselectivity (>99:1) via a vinyl carbocation under mild conditions.

Metal-Free Catalytic Synthesis of Thiocarbamates Using Sodium Sulfinates as the Sulfur Source.

A novel molecular iodine-catalyzed protocol for the construction of thiocarbamates from readily available sodium sulfinates, isocyanides, and water has been described. The present methodology offers a facile and practical route to a variety of thiocarbamates in moderate to good yields with favorable functional group tolerance by use odorless sodium sulfinates as the sulfur source. The mechanistic studies suggest the present transformation involves a radical process.

Intermolecular Regio- and Stereoselective Hetero-[5+2] Cycloaddition of Oxidopyrylium Ylides and Cyclic Imines.

We have developed the first intermolecular hetero-[5+2] cycloaddition reaction between oxidopyrylium ylides and cyclic imines with excellent control of regio- and stereoselectivity. Surprisingly, divergent stereochemistry was observed depending on the substitution pattern of the oxidopyrylium ylide. This new reaction provides quick access to highly substituted nitrogen-containing seven-membered rings-azepanes. Notably, a broad range of oxidopyrylium ylides and cyclic imines participate in this novel hetero-[5+2] cycloaddition reaction and the cycloadducts can be readily transformed into the core skeletons of bioactive natural products. DFT calculations revealed that the cycloaddition proceeds through a stepwise pathway and the imine nitrogen atom serves as the nucleophile to initiate the cycloaddition.

Copper-Catalyzed Regioselective Cleavage of C-X and C-H Bonds: A Strategy for Sulfur Dioxide Fixation.

The first example of direct fixation of sulfur dioxide between heteroaryls and aryl halides has been developed via copper-catalyzed regioselective cleavage of C-X and C-H bonds under base-free and ligand-free conditions by using DABSO (1,4-diazabicyclo[2.2.2]octane bis(sulfur dioxide)) as a solid and bench-stable sulfur dioxide surrogate. This mild protocol results in double C-S bond-forming reactions from simple precursors in the absence of prefunctionalized organometallic reagents, arenediazonium salts, and iodonium salts which extends the still limited number of sulfur dioxide fixation strategies.

Catalyst-free synthesis of α-thioacrylic acids via cascade thiolation and 1,4-aryl migration of aryl alkynoates at room temperature.

A simple and facile catalyst-free method for the construction of α-thioacrylic acids has been developed from readily-available aryl alkynoates and thiols at room temperature. Various α-thioacrylic acids could be conveniently and efficiently obtained in moderate to good yields via cascade thiolation and 1,4-aryl migration of aryl alkynoates in the absence of any catalyst and additive.

Transition-metal-free KI-catalyzed regioselective sulfenylation of 4-anilinocoumarins using Bunte salts.

An efficient and eco-friendly protocol for the KI-catalyzed regioselective sulfenylation of 4-anilinocoumarins with Bunte salts was established. The reaction worked smoothly under metal-free conditions and afforded a wide range of sulfenylated 4-anilinocoumarins with potential bioactivity in moderate to excellent yields. This method would expand the still limited scope of synthesis methods for C-S bond formation using Bunte salts.

Copper-Catalyzed Selenylation of Imidazo[1,2-a]pyridines with Selenium Powder via a Radical Pathway.

A convenient and efficient approach for the formation of nitrogen heterocycle-fused imidazo[1,2-a]pyridine and benzo[b]selenophenes has been developed through copper-catalyzed direct selenylation of readily available 2-(2-bromophenyl)imidazo[1,2-a]pyridines via regioselective cleavage of C(sp2)-Br and C(sp2)-H bonds using readily available selenium powder as the selenylating reagents under ligand- and base-free conditions in air. Preliminary mechanistic investigations indicated that radical species were involved in the present transformation.

Metal-free Oxidative Coupling of Aromatic Alkenes with Thiols Leading to (E)-Vinyl Sulfones.

A facile I2O5-mediated direct oxidative coupling of aromatic alkenes with thiols toward vinyl sulfones has been developed under metal-free conditions. This methodology provides a convenient and efficient approach to various (E)-vinyl sulfones from readily available starting materials with excellent regioselectivity. The present oxidative coupling reaction, not only expands the scope of functionalization of alkenes with thiols, but also makes it a practical and powerful complement to traditional methods for the synthesis of (E)-vinyl sulfones.

Metal-free I2O5-mediated direct construction of sulfonamides from thiols and amines.

A simple and convenient method has been developed for the construction of sulfonamides via I2O5-mediated sulfonylation of amines with arylthiols. The present protocol provides an attractive approach to sulfonamides in moderate to good yields from readily accessible and easy to handle starting materials under mild and metal-free conditions.

Label-free fluorescence turn-on aptasensor for prostate-specific antigen sensing based on aggregation-induced emission-silica nanospheres.

Fluorescent light-up probes based on aggregation-induced emission (AIE)-active molecules have recently attracted great research interest due to the intelligent fluorescence activation mechanism and high sensitivity. In this work, an AIE-silica nanosphere (SiO2 NP)-based label-free fluorescent aptasensor for the sensitive "turn-on" detection of prostate-specific antigen (PSA) is reported for the first time. The positively charged amino-functionalized SiO2 NPs were used as efficient nanocapturer to electrostatically adsorb single-stranded PSA aptamer (PA) to form SiO2 NP-PA nanocomposite as well as adsorb negatively charged tetraphenylethylene derivative 3 (TPE3) to form AIE-SiO2 NP nanocomposite. The binding of the aptamer to the target PSA could induce a rigid aptamer conformation, resulting in the release of the PA away from the surface of SiO2 NPs. This made the AIE molecules TPE3 aggregate on the SiO2 NP surface and emit high fluorescence. With the advantages of simple design and rapid responses, the proposed aptasensor showed high sensitivity and selectivity for PSA with a detection limit of 0.5 ng/mL. The aptasensor was further applied in human serum samples with satisfactory results. Given its versatility, high selectivity, and sensitivity, the proposed method could be extended to other targets by varying the recognition probes. Graphical abstract An AIE-SiO2 NP-based label-free fluorescent aptasensor for the sensitive "turn-on" detection of PSA is reported for the first time.

Molecular Iodine-Mediated Difunctionalization of Alkenes with Nitriles and Thiols Leading to ß-Acetamido Sulfides.

A direct difunctionalization protocol of alkenes with nitriles and thiols toward ß-acetamido sulfide derivatives has been proposed under metal-free synthesis conditions. The present protocol provides the facile and highly efficient synthesis of various ß-acetamido sulfides in a scaled-up manner with good to excellent yields simply using inexpensive molecular iodine as a catalyst, DMSO as a mild oxidant, and readily available thiols as thiolating reagents.

NBS/DBU mediated one-pot synthesis of α-acyloxyketones from benzylic secondary alcohols and carboxylic acids.

A simple and efficient one-pot NBS/DBU-mediated method has been developed for the synthesis of α-acyloxyketones from various benzylic secondary alcohols and carboxylic acids. Through this methodology, a series of α-acyloxyketones could be obtained in good to excellent yields under mild conditions. Importantly, this new reaction avoids the direct usage of toxic metal catalysts or potentially dangerous peroxide oxidants.

An efficient route to regioselective functionalization of benzo[b]thiophenes via palladium-catalyzed decarboxylative Heck coupling reactions: insights from experiment and computation.

Pd-catalyzed decarboxylative Heck-type coupling of 3-chlorobenzo[b]thiophene-2-carboxylic acids with styrenes have been developed as an efficient strategy for the construction of functionalized benzo[b]thiophenes. Theoretical analysis shows that AgCl generated during the reaction, instead of Pd, π-coordinates with the carboxyl O atom, making easy the rate-determining CO2 dissociation. The divergent reactivities of the Cl-substituted and H-substituted 3-benzo[b]thiophene-2-carboxylic acids are mainly due to the presence of the Cl substituent, which reduces the adjacent π-π interplay, thereby significantly contributing to decarboxylation. Therefore, the presence of both AgCl and the Cl substituent are of key importance in ensuring the occurrence of the reaction under the given conditions.

Catalyst-Free Regioselective C-3 Thiocyanation of Imidazopyridines.

A direct and straightforward approach for highly regioselective thiocyanation of imidazoheterocycles through sp(2) C-H functionalization has been realized at room temperature. Various C-3 thiocyanated imidazopyridines are formed in moderate to good yield. The present method exhibits a mild and selective access to a variety of imidazopyridine derivatives of pharmacological interest.

Metal-Free Oxidative Spirocyclization of Alkynes with Sulfonylhydrazides Leading to 3-Sulfonated Azaspiro[4,5]trienones.

A novel and direct oxidative spirocyclization of arylpropiolamides with sulfonylhydrazides leading to 3-sulfonated azaspiro[4,5]trienones has been developed under metal-free conditions. The reaction is performed in a tandem manner constituted by the sequential sulfonylation of alkynes, ipso-carbocyclization, dearomatization, hydration, and oxidation processes, providing a convenient and efficient approach to various sulfonated azaspiro[4,5] trienones of biological importance.

Metal-Free Iodine-Catalyzed Direct Arylthiation of Substituted Anilines with Thiols.

Iodine-catalyzed direct arylthiation of substituted anilines for the synthesis of various diaryl sulfides has been developed under metal- and solvent-free conditions. The present method uses readily available thiols as the arylthiation reagents, and environmentally friendly and inexpensive I2 as the catalyst. Importantly, no base or ligand was necessary. Such a simple, efficient, and economical transformation provides an attractive approach to various diaryl sulfides in good to excellent yields.