Selective Increase in CO2 Electroreduction to Ethanol Activity at Nanograin-Boundary-Rich Mixed Cu(I)/Cu(0) Sites via Enriching Co-Adsorbed CO and Hydroxyl Species.

Selective producing ethanol from CO2 electroreduction is highly demanded, yet the competing ethylene generation route is commonly more thermodynamically preferred. Herein, we reported an efficient CO2-to-ethanol conversion (53.5 % faradaic efficiency at -0.75 V versus reversible hydrogen electrode (vs. RHE)) over an oxide-derived nanocubic catalyst featured with abundant "embossment-like" structured grain-boundaries. The catalyst also attains a 23.2 % energy efficiency to ethanol within a flow cell reactor. In situ spectroscopy and electrochemical analysis identified that these dualphase Cu(I) and Cu(0) sites stabilized by grain-boundaries are very robust over the operating potential window, which maintains a high concentration of co-adsorbed *CO and hydroxyl (*OH) species. Theoretical calculations revealed that the presence of *OHad not only promote the easier dimerization of *CO to form *OCCO (ΔG~0.20 eV) at low overpotentials but also preferentially favor the key *CHCOH intermediate hydrogenation to *CHCHOH (ethanol pathway) while suppressing its dehydration to *CCH (ethylene pathway), which is believed to determine the remarkable ethanol selectivity. Such imperative intermediates associated with the bifurcation pathway were directly distinguished by isotope labelling in situ infrared spectroscopy. Our work promotes the understanding of bifurcating mechanism of CO2ER-to-hydrocarbons more deeply, providing a feasible strategy for the design of efficient ethanol-targeted catalysts.

Recognition Site Modifiable Macrocycle: Synthesis, Functional Group Variation and Structural Inspection.

Traditional macrocyclic molecules encode recognition sites in their structural backbones, which limits the variation of the recognition sites and thus, would restrict the adjustment of recognition properties. Here, we report a new oligoamide-based macrocycle capable of varying the recognition functional groups by post-synthesis modification on its structural backbone. Through six steps of common reactions, the parent macrocycle (9) can be produced in gram scale with an overall yield of 31%. The post-synthesis modification of 9 to vary the recognition sites are demonstrated by producing four different macrocycles (10-13) with distinct functional groups, 2-methoxyethoxyl (10), hydroxyl (11), carboxyl (12) and amide (13), respectively. The 1H NMR study suggests that the structure of these macrocycles is consistent with our design, i.e., forming hydrogen bonding network at both rims of the macrocyclic backbone. The 1H-1H NOESY NMR study indicates the recognition functional groups are located inside the cavity of macrocycles. At last, a preliminary molecular recognition study shows 10 can recognize n-octyl-ß-D-glucopyranoside (14) in chloroform.

Defluorinative Multi-Functionalization of Fluoroaryl Sulfoxides Enabled by Fluorine-Assisted Temporary Dearomatization.

Owing to its unique physical properties, fluorine is often used to open up new reaction channels. In this report, we establish a cooperation of [5,5]-rearrangement and fluorine-assisted temporary dearomatization for arene multi-functionalization. Specifically, the [5,5]-rearrangement of fluoroaryl sulfoxides with ß,γ-unsaturated nitriles generates an intriguing dearomatized sulfonium species which is short-lived but exhibits unusually high electrophilicity and thus can be instantly trapped by nucleophiles and dienes at a remarkably low temperature (-95 °C) to produce four types of valuable multi-functionalized benzenes, respectively, involving appealing processes of defluorination, desulfurization, and sulfur shift. Mechanistic studies indicate that the use of fluorine on arenes not only circumvents the generally inevitable [3,3]-rearrangement but also impedes the undesired rearomatization process, thus provides a precious space for constructing and elaborating the temporarily dearomatized fluorinated sulfonium species.

Efficient and Selective Electroreduction of CO2 to HCOOH over Bismuth-Based Bromide Perovskites in Acidic Electrolytes.

Metal halide perovskites, primarily used as optoelectronic devices, have not been applied for electrochemical conversion due to their insufficient stability in moisture. Herein, two bismuth-based perovskites are introduced as novel electrocatalysts to convert CO2 into HCOOH in aqueous acidic media (pH 2.5), exhibiting a high Faradaic efficiency for HCOOH of >80 % in a wide potential range from -0.75 to -1.25 V. Their structural evolution against water was dynamically monitored by in situ spectra. Theoretical calculations further reveal that the formation of intermediate OCHO* on bismuth sites of Cs3 Bi2 Br9 (111) play a pivotal role toward HCOOH production, which has a lower energy barrier than that on Cs2 AgBiBr6 (001) surfaces. Significantly, CO2 reacts with protons instead of water which can enhance CO2 reduction rate and suppress hydrogen evolution by avoiding carbonate formation in acidic electrolytes. This work paves the way for the extensive investigation of halide perovskites in aqueous systems.

Z-Selective α-Arylation of α,ß-Unsaturated Nitriles via [3,3]-Sigmatropic Rearrangement.

The Morita-Baylis-Hillman (MBH) reaction and [3, 3]-sigmatropic rearrangement are two paradigms in organic synthesis. We have merged the two types of reactions to achieve [3,3]-rearrangement of aryl sulfoxides with α,ß-unsaturated nitriles. The reaction was achieved by sequentially treating both coupling partners with electrophilic activator (Tf2 O) and base, offering an effective approach to prepare synthetically versatile α-aryl α,ß-unsaturated nitriles with Z-selectivity through direct α-C-H arylation of unmodified α,ß-unsaturated nitriles. The control experiments and DFT calculations support a four-stage reaction sequence, including the assembly of Tf2 O activated aryl sulfoxide with α,ß-unsaturated nitrile, MBH-like Lewis base addition, [3,3]-rearrangement, and E1cB-elimination. Among these stages, the Lewis base addition is diastereoselective and E1cB-elimination is cis-selective, which could account for the remarkable Z-selectivity of the reaction.

Morita-Baylis-Hillman-Type [3,3]-Rearrangement: Switching from Z- to E-Selective α-Arylation by New Rearrangement Partners.

α-aryl α,ß-unsaturated carbonyls represent an important class of derivatizable synthetic intermediates, however, the synthesis of such compounds still remains a challenge. Recently, we showcased a novel Z-selective α-arylation of α,ß-unsaturated nitriles with aryl sulfoxides via [3,3]-rearrangement involving an Morita-Baylis-Hillman (MBH) process. Herein, we demonstrate the feasibility of reversing the stereoselectivity of such MBH-type [3,3]-rearrangement by switching to a new pair of rearrangement partners consisting of aryl iodanes and α,ß-unsaturated oxazolines. As a result, the two protocols complement each other in approaching E- or Z-α-aryl α,ß-unsaturated carbonyl derivatives. Mechanistic studies reveal a possible reaction pathway and provide an explanation for the opposite stereoselectivities.

Asymmetric Iodonio-[3,3]-Sigmatropic Rearrangement to Access Chiral α-Aryl Carbonyl Compounds.

Here we describe an asymmetric [3,3]-sigmatropic rearrangement of aryl iodanes that enables the enantioselective α-arylation of chiral 2-oxazolines, thereby producing valuable chiral α-aryl carbonyl compounds. The success of this protocol hinges on the selective assembly of aryl iodanes with 2-oxazolines and the smooth deprotonation of the in situ-generated iodonium-imine species. The nearly neutral and mild conditions of the reaction allow it to tolerate a wide variety of functional groups. Moreover, the remaining iodine atom in the products not only provides a versatile platform for further elaboration of such molecules but also supplies the asymmetric hypervalent iodine chemistry with a new class of chiral scaffolds.

Selective [5,5]-Sigmatropic Rearrangement by Assembly of Aryl Sulfoxides with Allyl Nitriles.

Aromatic [5,5]-sigmatropic rearrangement is an appealing protocol for accessing 1,4-substituted arenes. However, such a protocol has not been well utilized in organic synthesis because of the difficulties in the synthesis of the substrates, selectivity issues, and limited substrate scope. Described herein is a new [5,5]-sigmatropic reaction utilizing readily available aryl sulfoxides and allyl nitriles. This reaction features mild reaction conditions, high chemo- and regioselectivity, excellent functional-group compatibility, and broad substrate scope. Computational studies suggest that the success of the reaction can be attributed to the selective electrophilic assembly of the rearrangement precursors, in which a linear -C=C=N- linkage favors [5,5]-sigmatropic rearrangement over the competitive [3,3]-sigmatropic rearrangement.

The ortho-Difluoroalkylation of Aryliodanes with Enol Silyl Ethers: Rearrangement Enabled by a Fluorine Effect.

Presented herein is an intriguing effect of fluorine, and it allows difluoroenol silyl ethers to couple with aryliodanes in a redox-neutral manner to afford ortho-iodo difluoroalkylated arenes. The remaining iodide group provides a versatile platform for converting the products into various valuable difluoroalkylated arenes. The reaction shows excellent functional-group compatibility and broad substrate scope. A DFT mechanistic study suggests that the fluorine effect facilitates a subtle nucleophilic attack of the oxygen atom of enol silyl ethers onto aryliodanes, therefore leading to a rearrangement.

Dearomative Dual Functionalization of Aryl Iodanes.

Herein we describe the dearomatization of aryl iodanes through an unprecedented "rearrangement/addition" sequence. The process consists of two stages. First, a rapid [3,3] sigmatropic rearrangement of the aryl iodane with an α-stannyl nitrile affords a highly electrophilic dearomatized intermediate at -78 °C. A low-temperature rearrangement then enables the unstable dearomatized species to be trapped in situ with various nucleophiles. As a consequence, the reaction not only breaks the aromaticity of the aryl iodane but also sequentially installs two different functional groups, thus resulting in a polysubstituted alicyclic product.

Selective ortho C-H Cyanoalkylation of (Diacetoxyiodo)arenes through [3,3]-Sigmatropic Rearrangement.

We herein report a robust catalyst-free cross-coupling between ArI(OAc)2 and α-stannyl nitriles, aided by TMSOTf. The transformation introduces a cyanoalkyl group to the ortho position of ArI(OAc)2 and simultaneously reduces the aryl iodine(III) to iodide, thus providing α-(2-iodoaryl) nitrile as the product. This transformation could be completed within 5 min at -78 °C and features superb functional-group tolerance and efficient scalability. DFT calculations indicate that the formation of a ketenimine(aryl)iodonium intermediate and subsequent [3,3]-sigmatropic rearrangement are involved as key steps.

Redox-Neutral α-Arylation of Alkyl Nitriles with Aryl Sulfoxides: A Rapid Electrophilic Rearrangement.

A facile α-arylation of nitriles has been developed by simply introducing Tf2O and DABCO to the mixture of nitriles and aryl sulfoxides. The transformation consists of two sequential steps: (i) Tf2O-initiated electrophilic assembly and and (ii) DABCO-triggered rearrangement. Each step can be tuned independently by changing the temperature and/or base. This adjustability allows the method to accommodate a wide range of substrates. Notable features of this new protocol include remarkable efficiency (20 min, -30 °C), exclusive regioselectivity, and high functional group compatibility, which can be challenging issues in traditional approaches. NMR studies not only identified a unique, highly unstable sulfonium imine complex but also demonstrated the importance of temperature in the formation and manipulation of this key intermediate. Further DFT calculations suggested that an electrophilic assembly, followed by removal of HOTf (by base), and finally [3,3]-sigmatropic rearrangement are three key stages in the reaction. The versatile transformability of the products and easy scalability of this reaction are also exhibited here.

Palladium-catalyzed tandem cyclization/sulfonylation of homoallenyl amides with sodium sulfinates.

A palladium-catalyzed cyclizative sulfonylation of homoallenyl amides using sodium sulfinates as the sulfonylation reagent and PhI(O2CCF3)2 as the oxidant has been realized. The reaction proceeds at room temperature and produces structurally diverse 2-amino-5-sulfonylmethylfurans in good to excellent yields. A Pd(ii)/Pd(iv) catalytic cycle has been proposed for the formation of sulfonylated furans. The concurrent formation of a furan moiety and a C(sp3)-sulfur bond in a single operation makes it a very attractive method for organic synthesis.

Phytotoxic, Antifungal and Immunosuppressive Metabolites from Aspergillus terreus QT122 Isolated from the Gut of Dragonfly.

Insect gut microbes have been considered as a resource for bioactive metabolites. The aim of this study was to characterize the compounds of a fungus Aspergillus terreus QT122 associated with the gut of dragonfly. Five main phytotoxic, antifungal, and immunosuppressive substances were isolated from the fungus QT122. The structures of such compounds were identified as emodin (1), 1-methyl emodin (2), terrein (3), methyl 6-acetyl-4-methoxy-7,8-dihydroxynaphthalene-2-carboxylate (4), and dihydrogeodin (5) on the basis of spectroscopic analysis and by comparison of the corresponding data to those reported in the literature previously. The compound 3 exhibited the best phytotoxic activity against the radicle growth of A. retroflexus L. and E. crusgalli L. with their IC50 values of 11.2 and 3.1 µg/mL, which were comparable to that of the positive control of 2,4-dichlorophenoxyacetic acid (2,4-D) with the IC50 values of 8.1 and 1.6 µg/mL, respectively. The compounds 2-3 showed potent antifungal activity in the growth of Alternaria solani with the IC50 value of less than 0.1 µg/mL and the compound 2 also had great inhibitory effect against the growth of Fusarium oxysporum f. sp. cucumerinum (IC50 < 0.1 µg/mL), which was comparable to that of referenced cycloheximide with IC50 value of below 0.1 µg/mL. The compounds 3-5 exhibited strong immunosuppressive activities against the T cell viability with the inhibition rates of more than 99%, which were comparable to positive cyclosporin A under the concentration of 20 µM. These results suggest that the compounds 2-5 have the potential to be used as bio-control agents in agriculture or immunosuppressive agents.

Direct access to 2-amino-5-azidomethylfurans through palladium-catalyzed azidative cycloisomerization of homoallenyl amides.

A room temperature, efficient, and palladium-catalyzed azidative cycloisomerization of homoallenyl amides using TMSN3 as the azidation reagent and PhI(O2CCF3)2 as the oxidant is described, producing a variety of 2-amino-5-azidomethylfurans in moderate to excellent yields. The products can be applied to the concise synthesis of 1,2,3-triazoles via a Cu-catalyzed azide-alkyne cycloaddition.

A regio- and stereoselective entry to (Z)-ß-halo alkenyl sulfides and their applications to access stereodefined trisubstituted alkenes.

A mild and efficient preparation of (Z)-ß-halo alkenyl sulfides via the K2CO3-promoted hydrothiolation of haloalkynes has been realized, producing (Z)-ß-bromo and (Z)-ß-chloro vinylic sulfides in high yields with excellent regio- and stereoselectivity. This approach covers a variety of substrates, including both aryl and alkyl haloalkynes. Meaningfully, it allows a facile access to stereodefined (Z)- or (E)-trisubstituted olefins featuring the iterative cross-coupling of carbon-halide and carbon-sulfur bonds of ß-halo alkenyl sulfides.

Highly Efficient One-Pot Synthesis of 2,4,5-Trisubstituted 3(2H)-Furanones Utilizing a Au(I)-Catalyzed Oxidation/Pinacol Rearrangement/anti-Michael Cascade.

A highly efficient Au(I)-catalyzed cascade reaction between bispropargylic alcohols and pyridine-N-oxides has been realized. The reaction process involved a gold(I)-catalyzed sequential oxidation/Pinacol rearrangement/oxacyclization. Moreover, 1,2-aryl, 1,2-alkyl, or 1,2-vinyl migration was favored over 1,2-alkynyl in the crucial gold(I)-catalyzed Pinacol rearrangement step. A range of 2,4,5-trisubstituted 3(2H)-furanones were synthesized in high yields (up to 88%) with excellent regioselectivities (up to >19:1) under mild reaction conditions.

Cu-catalyzed cascade difluoroalkylation/5-endo cyclization/ß-fluorine cleavage of ynones.

A copper-catalyzed, redox-neutral cascade difluoroalkylation/5-endo annulation/ß-fluorine cleavage of ynones is developed, providing a direct and stereoselective method to access synthetically important α-monofluoroalkenyl cyclopentanones. Mechanistic studies suggest an unprecedented CuII-assisted ß-fluorine fragmentation, which may be valuable for the challenging but important C-F bond activation. Moreover, the in situ generated difluorocarbene was found to serve as an effective reductant for the regeneration of copper(I) catalyst, thus avoiding the addition of external reductants.

Sulfur(iv)-mediated umpolung α-heterofunctionalization of 2-oxazolines.

The α-umpolung of carbonyl compounds significantly expands the boundaries of traditional carbonyl chemistry. Despite various umpolung methods available today, reversing the inherent reactivity of carbonyls still remains a substantial challenge. In this article, we report the first use of sulfonium salts, in lieu of well-established hypervalent iodines, for the carbonyl umpolung event. The protocol enables the incorporation of a wide variety of heteroatom nucleophiles into the α-carbon of 2-oxazolines. The success of this investigation hinges on the following factors: (1) the use of sulfoxides, which are abundant, structurally diverse and tunable, and easily accessible, ensures the identification of a superior oxidant namely phenoxathiin sulfoxide for the umpolung reaction; (2) the "assembly/deprotonation" protocol previously developed for rearrangement reactions in our laboratory was successfully applied here for the construction of α-umpoled 2-oxazolines.

Dearomative di- and trifunctionalization of aryl sulfoxides via [5,5]-rearrangement.

Aromatic [5,5]-rearrangement can in principle be an ideal protocol to access dearomative compounds. However, the lack of competent [5,5]-rearrangement impedes the advance of the protocol. In this Article, we showcase the power of [5,5]-rearrangement recently developed in our laboratory for constructing an intriguing dearomative sulfonium specie which features versatile and unique reactivities to perform nucleophilic 1,2- and 1,4-addition and cyclization, thus achieving dearomative di- and trifunctionalization of easily accessible aryl sulfoxides. Impressively, the dearomatization products can be readily converted to sulfur-removed cyclohexenones, naphthalenones, bicyclic cyclohexadienones, and multi-substituted benzenes. Mechanistic studies shed light on the key intermediates and the remarkable chemo-, regio- and stereoselectivities of the reactions.