Ligand-Controlled Cobalt-Catalyzed Regiodivergent and Stereoselective Ring-Opening Isomerization of Vinyl Cyclopropanes.

A ligand-controlled regiodivergent and stereoselective ring-opening isomerization of vinylcyclopropane was developed with cobalt catalysis. Employing the commercially available Xantphos ligand, the reactions afforded exclusively linear-type 1,3-dienes as the products. Interestingly, when switching the ligand to an amido-diphosphine ligand (PNP), branched-type 1,3-dienes were obtained with high regioselectivity and stereoselectivity. Preliminary mechanistic investigations suggested that a π-allyl metal and a metal-hydride species are involved as key intermediates in the two transformations, respectively.

Cyclization Reactions of In Situ-Generated Acyl Ketene with Ynones to Form Oxacycles.

Acyl ketenes react with polar unsaturated functional groups to give unique heterocyclic rings, yet reactions with unpolarized unsaturated functional groups have not been reported. Herein, we describe two effective ring-forming reactions between acetyl ketene and electron-deficient alkynes. The first reaction involves in situ tethering between acetyl ketene and nucleophile-containing 1,3-diynones, which promotes sequential intramolecular 1,6/1,4-additions to generate 2-methylene-2H-pyrans in various yields (24-91%). The other involves a zwitterionic intermediate generated from acetyl ketene and DABCO, which undergoes a Michael addition with terminal alkynyl ketones to generate 3-acyl-4-pyrones (11-79%).

Photoredox-Catalyzed Hydroacylation of Azobenzenes with Carboxylic Acids.

Acyl hydrazides are widely found in bioactive compounds and have important applications as versatile synthetic intermediates. In the current report, a photoredox-catalyzed hydroacylation of azobenzenes was disclosed with carboxylic acids as the acylation reagent, affording a variety of N,N'-disubstituted hydrazides. The process possesses the advantages of mild reaction conditions, broad substrate scope, and high efficiency. Preliminary mechanistic investigation indicated that the addition of an acyl radical to the azo compound should be involved.

A General Protocol toward Synthesis of 3-Methylindoles Using Acenaphthoimidazolyidene-Ligated Oxazoline Palladacycle.

An efficient catalytic strategy toward the synthesis of N-substituted 3-methylindoles from inactive o-dihaloarenes and N-allylamines was developed by using a 1,3-bis(2,6-diisopropylphenyl)acenaphthoimidazol-2-ylidene (AnIPr)-ligated oxazoline palladacycle. It enabled a very broad substrate scope tolerating different functional groups, electronic properties, and steric bulkiness and afforded desired products in good to excellent yields. Importantly, it showed great potential to synthesize several bioactive compounds and key intermediates of natural products in high yields.

Study on the Dynamic Changes in Non-Volatile Metabolites of Rizhao Green Tea Based on Metabolomics.

The processing of tea leaves plays a crucial role in the formation of the taste of the resulting tea. In order to study the compositions of and changes in taste-related substances during the processing of Rizhao green tea, non-targeted metabolomics was used, based on UHPLC-Q Exactive MS. Totals of 529, 349, and 206 non-volatile metabolites were identified using three different detection modes, of which 112 secondary metabolites were significantly changed. Significant variations in secondary metabolites were observed during processing, especially during the drying stage, and the conversion intensity levels of non-volatile metabolites were consistent with the law of "Drying > Fixation > Rolling". The DOT method was used to screen tea-quality-related compounds that contributed significantly to the taste of Rizhao green tea, including (-)-epicatechin gallate, (-)-epicatechin gallate, gallic acid, L-theanine, and L-leucine, which make important contributions to taste profiles, such as umami and bitterness. Metabolic pathway analysis revealed that purine metabolism, caffeine metabolism, and tyrosine metabolism perform key roles in the processing of Rizhao green tea in different processing stages. The results of this study provide a theoretical basis for tea processing and practical advice for the food industry.

Condition-Controlled O-Acylation and N-O Bond Reduction of Hydroximic Acids with Thioacetic Acid.

Condition-dependent transformations between hydroximic acids and thioacetic acid were achieved. Using NH4HCO3 in the ethanol solvent, efficient N-O bond cleavage of hydroxamic acids occurred to afford primary amides with high functional group compatibility. The reaction was switched to O-acylation when NEt3 and H2O were used as the base and solvent, respectively. These facile transformations could be scaled up to the gram level smoothly. Preliminary mechanistic studies suggested that the N-O bond cleavage involves a cascade process of acylation/reduction.

Cobalt-Catalyzed Asymmetric Hydrosilylation of α-Oxygenated Ketones.

An asymmetric hydrosilylation of α-oxygenated ketones was developed under the catalysis of Co(OAc)2 in combination with a chiral phosphine-amido-oxazoline (PAO) ligand, providing a mild, efficient, and enantioselective access to a variety of synthetically useful 1,2-diol derivatives. This protocol can be carried out at the gram scale with a catalyst loading of 1 mol %, and its synthetic utility was demonstrated by efficient conversion of the optically enriched products into chiral α-hydroxy acid, 1,3-dioxolan-2-one, ethylene oxide, and 1,2,3-1H-triazole.

Cycloisomerization of Alkyne-Tethered N-Acyloxycarbamates to 2-(3H)Oxazolones through Nitrenoid-Mediated Carboxyamidation.

The cycloisomerization of alkyne-tethered N-benzoyloxycarbamates to 2-(3H)oxazolones is described. Two catalytic systems are tailored for intramolecular 5-exo-alkyne carboxyamidation and concomitant alkene isomerization. PtCl2 /CO (5 mol%, toluene, 100 °C) promotes both carboxyamidation and alkene isomerization but has a limited substrate scope. On the other hand, FeCl3 (5 mol%, CH3 CN, 100 °C) promotes carboxyamidation effectively but a cocatalyst is required for the exocyclic alkene isomerization. Thus, a two-step one-pot protocol has been developed for a broader reaction scope, which involves FeCl3 -catalyzed carboxyamidation and base-induced alkene isomerization. Crossover experiments suggest that these reactions proceed mainly through a mechanism involving acylnitrenoid intermediates rather than carbenoid intermediates.

Visible-Light-Promoted Hydrogenation of Azobenzenes to Hydrazobenzenes with Thioacetic Acid as the Reductant.

A catalyst- and metal-free hydrogenation of azobenzenes to hydrazobenzenes in the presence of thioacetic acid was achieved under visible light irradiation. The transformation was carried out under mild conditions in an air atmosphere at ambient temperature, generating a variety of hydrazobenzenes with yields up to 99%. The current process is compatible with a variety of substituents and is highly chemoselective for azo reduction when other unsaturated functionalities (carbonyl, alkenyl, alkynyl, etc.) are contained. Preliminary mechanistic study indicated that the transformation could be a radical process.

Covalent transfer of chemical gradients onto a graphenic surface with 2D and 3D control.

Control over the functionalization of graphenic materials is key to enable their full application in electronic and optical technologies. Covalent functionalization strategies have been proposed as an approach to tailor the interfaces' structure and properties. However, to date, none of the proposed methods allow for a covalent functionalization with control over the grafting density, layer thickness and/or morphology, which are key aspects for fine-tuning the processability and performance of graphenic materials. Here, we show that the no-slip boundary condition at the walls of a continuous flow microfluidic device offers a way to generate controlled chemical gradients onto a graphenic material with 2D and 3D control, a possibility that will allow the sophisticated functionalization of these technologically-relevant materials.

Defect-engineered surfaces to investigate the formation of self-assembled molecular networks.

Herein we report the impact of covalent modification (grafting), inducing lateral nanoconfinement conditions, on the self-assembly of a quinonoid zwitterion derivative into self-assembled molecular networks at the liquid/solid interface. At low concentrations where the compound does not show self-assembly behaviour on bare highly oriented pyrolytic graphite (HOPG), close-packed self-assembled structures are visualized by scanning tunneling microscopy on covalently modified HOPG. The size of the self-assembled domains decreases with increasing the density of grafted molecules, i.e. the molecules covalently bound to the surface. The dynamics of domains are captured with molecular resolution, revealing not only time-dependent growth and shrinkage processes but also the orientation conversion of assembled domains. Grafted pins play a key role in initiating the formation of on-surface molecular self-assembly and their stabilization, providing an elegant route to study various aspects of nucleation and growth processes of self-assembled molecular networks.

Iron(II)-Catalyzed Nitrene Transfer Reaction of Sulfoxides with N-Acyloxyamides.

An iron(II)-catalyzed nitrene transfer reaction of sulfoxides with N-acyloxyamides has been developed, leading to the efficient construction of N-acyl sulfoximines with high functional-group compatibility. The current catalytic transformation was carried out under an air atmosphere at ambient temperature and could be scaled up to gram scale with a catalyst loading of 1 mol %. Application of the methodology was demonstrated by facile C-H acetoxylation and olefination using the N-acyl sulfoximine as the directing group.

Development of an Allenyne-Alkyne [4+2] Cycloaddition and its Application to Total Synthesis of Selaginpulvilin A.

A new [4+2] cycloaddition of allenyne-alkyne is developed. The reaction is believed to proceed with forming an α,3-dehydrotoluene intermediate. This species behaves as a σπ-diradical to react with a hydrogen atom donor, whereas it displays a zwitterionic reactivity toward weak nucleophiles. The efficiency of trapping α,3-dehydrotoluene depends not only on its substituents but also the trapping agents. Notable features of the reaction are the activating role of the extra alkyne of the 1,3-diyne that reacts with the allenyne moiety and the opposite mode of trapping with oxygen and nitrogen nucleophiles. Oxygen nucleophiles result in the oxygen-end incorporation at the benzylic position of the α,3-dehydrotoluene, whereas with amine nucleophiles the nitrogen-end is incorporated into the aromatic core. Relying on the allenyne-alkyne cycloaddition as an enabling strategy, a concise total synthesis of phosphodiesterase-4 inhibitory selaginpulvilin A is realized.

Construction of N-Acyliminophosphoranes via Iron(II)-Catalyzed Imidization of Phosphines with N-Acyloxyamides.

Employing FeCl2 as a cheap and readily available catalyst, a facile imidization of phosphines with N-acyloxyamides is described, affording synthetically useful N-acyliminophosphoranes with high functional group tolerance. The transformation is easily performed under an air atmosphere at room temperature and could be scaled up to gram scale with a catalyst loading of 1 mol %. The iminophosphoranyl moiety in the product was further utilized as an effective directing group for controllable ortho C(sp2)-H bond amidations under Rh(III) catalysis.

Grafting Ink for Direct Writing: Solvation Activated Covalent Functionalization of Graphene.

Covalent functionalization of graphene (CFG) has shown attractive advantages in tuning the electronic, mechanical, optical, and thermal properties of graphene. However, facile, large-scale, controllable, and highly efficient CFG remains challenging and often involves highly reactive and volatile compounds, requiring complex control of the reaction conditions. Here, a diazonium-based grafting ink consisting of only two components, i.e., an aryl diazonium salt and the solvent dimethyl sulfoxide (DMSO) is presented. The efficient functionalization is attributed to the combination of the solvation of the diazonium cations by DMSO and n-doping of graphene by DMSO, thereby promoting electron transfer (ET) from graphene to the diazonium cations, resulting in the generation of aryl radicals which subsequently react with the graphene. The grafting density of CFG is controlled by the reaction time and very high levels of functionalization, up to the failing of the Tuinstra-Koenig (T-K) relation, while the functionalization layer remains at monolayer height. The grafting ink, effective for days at room temperature, can be used at ambient conditions and renders the patterning CFG by direct writing as easy as writing on paper. In combination with thermal sample treatment, reversible functionalization is possible by subsequent writing/erasing cycles.

Cobalt-Catalyzed Z to E Geometrical Isomerization of 1,3-Dienes.

An efficient cobalt-catalyzed geometrical isomerization of 1,3-dienes is described. In the combination of a CoCl2 precatalyst with an amido-diphosphine-oxazoline ligand, the geometrical isomerization of E/Z mixtures of 1,3-dienes proceed in a stereoconvergent manner, affording (E) isomers in high stereoselectivity. This facile transformation features a broad substrate scope with good functional group tolerance and could be scaled up to the gram scale smoothly with a catalyst loading of 1 mol %.

Lithium and magnesium complexes by using pyridyl-pendanted unsymmetrical ß-diketiminates: syntheses and application as catalysts for the hydroboration of carbonyl compounds.

The push for environmentally benign and sustainable chemical processes has reinforced the demand to displace transition metals with cheap, nontoxic and naturally abundant metals. To fulfil this requirement, we endeavored to synthesize alkali- and alkaline earth-metal complexes and employ them as catalysts for organic transformations. Two lithium and one magnesium complexes, which are supported by pyridyl-pendanted unsymmetrical ß-diketiminates, have been synthesized and characterized. They are formulated as [Li(L1)]2 (1), [Li(L2)]2 (2) and [Mg(L2)2]·0.5C6H14 (3) (HL1 = N{-4-[(2,6-diisopropylphenylamino)pent-3-en-2-ylidene]-6-methyl}pyridin-2-amine and HL2 = N-{4-[(2,6-diisopropylphenyl)imino]pent-2-en-2-yl}pyridin-2-amine). Complex 1 features two inequivalent Li(I) sites. One Li(I) center exhibits tetrahedral geometry, while the other Li(I) ion adopts a triangular coordination sphere. The catalytic activities of 1-3 toward the hydroboration of aldehydes and ketones by pinacolborane (HBpin) were investigated. Both dinuclear lithium complexes and homoleptic magnesium compound were found to be highly efficient catalysts for the hydroboration of aldehydes and ketones, affording the corresponding borate esters in good yields within a very short time. Synthetic application of the complexes was demonstrated by the gram-scale reduction of ketones via a one-pot two step reaction with only 0.2 mol% loading of 2. Mechanistic details for the hydroboration were revealed by DFT calculations.

A Unified Catalytic Asymmetric (4+1) and (5+1) Annulation Strategy to Access Chiral Spirooxindole-Fused Oxacycles.

A unified catalytic asymmetric (N+1) (N=4, 5) annulation reaction of oxindoles with bifunctional peroxides has been achieved in the presence of a chiral phase-transfer catalyst (PTC). This general strategy utilizes peroxides as unique bielectrophilic four- or five-atom synthons to participate in the C-C and the subsequent umpolung C-O bond-forming reactions with one-carbon unit nucleophiles, thus providing a distinct method to access the valuable chiral spirooxindole-tetrahydrofurans and -tetrahydropyrans with good yields and high enantioselectivities under mild conditions. DFT calculations were performed to rationalize the origin of high enantioselectivity. The gram-scale syntheses and synthetic utility of the resultant products were also demonstrated.

Amide/Ester Cross-Coupling via C-N/C-H Bond Cleavage: Synthesis of ß-Ketoesters.

Activated primary, secondary, and tertiary amides were coupled with enolizable esters in the presence of LiHMDS to obtain good yields of ß-ketoesters at room temperature. Notably, this protocol provides an efficient, mild, and high chemoselectivity method to synthesis of ß-alkylketoesters using the cross-coupling between aliphatic amides and esters. Meanwhile, gram-scale secondary and primary amides reacted via in situ generated activated tertiary amides and exhibited good reactivity when coupled with esters.