Physiological and Cellular Ultrastructural Responses of Isatis indigotica Fort. under Salt Stress.

This study aimed to analyze the effects of salt stress on the growth physiology and plant-cell ultrastructure of Isatis indigotica Fort. (I. indigotica) to evaluate its adaptability under salt stress. The effects of different concentrations of salt (NaCl; 0, 25, and 300 mmol·L-1) on the agronomic traits, activities of related enzymes, ion balance, and mesophyll-cell ultrastructure of I. indigotica were studied in a controlled pot experiment. Results showed that compared with those of the control group, the aerial-part fresh weight, underground fresh weight, tiller number, root length, root diameter, plant height, and leaf area of salt-stressed I. indigotica increased at 25 mmol·L-1 and then decreased at 300 mmol·L-1. The changes in levels of superoxide dismutase, peroxidase, ascorbate peroxidase, and catalase showed a similar trend, with significant differences compared with control group. Salt stress altered the ion balance of I. indigotica, resulting in a significant increase in Na+ content and a significant decrease in K+ content. The contents of Ca2+ and Mg2+ changed to varying degrees. The analysis of the microstructure of the root showed that under salt treatment, the epidermal cells of the root significantly thickened and the diameter of the xylem decreased. The results of ultrastructural analysis of mesophylls showed that salt stress can cause cell-membrane contraction, cell-gap enlargement, disorder in the structures of chloroplasts and mitochondria, and an increase in the number of osmiophilic particles. These changes were aggravated by the increase in NaCl concentration. This study reveals the response of I. indigotica to salt stress and provides a basis for further study on the salt-tolerance mechanism of I. indigotica.

Iron-Catalyzed Sulfonylthiocyanation of α,ß-Unsaturated Amides/Esters via the Insertion of Sulfur Dioxide.

An iron-catalyzed four-component sulfonylthiocyanation between α,ß-unsaturated amides/esters, TMSNCS, aryldiazonium tetrafluoroborates, and sulfur dioxide (from SOgen) is demonstrated. This protocol is characterized by mild reaction conditions, good functional group compatibility, broad substrate scope, and good to excellent yields, providing a feasible method for the preparation of ß-thiocyanated sulfone compounds. The preliminary mechanism investigation shows that a radical pathway may be involved in the process.

Redox-Neutral Rhodium(III)-Catalyzed Chemospecific and Regiospecific [4+1] Annulation between Indoles and Alkenes for the Synthesis of Functionalized Imidazo[1,5-a]indoles.

Exploiting internal alkenes embedded with an oxidizing function/leaving group as a rare and unconventional one-carbon unit, a redox-neutral rhodium(III)-catalyzed chemo- and regiospecific [4+1] annulation between indoles and alkenes for the synthesis of functionalized imidazo[1,5-a]indoles has been achieved. Internal alkenes employed here can fulfill an unusual [4+1] annulation rather than normal [4+2] annulation/C-H alkenylation. This method is characterized by excellent chemo- and regioselectivity, broad substrate scope, good functional group tolerance, good to high yields, and redox-neutral conditions.

Additive-Controlled Divergent Synthesis of Tetrasubstituted 1,3-Enynes and Alkynylated 3H-Pyrrolo[1,2-a]indol-3-ones via Rhodium Catalysis.

Herein, we report the additive-controlled divergent synthesis of tetrasubstituted 1,3-enynes and alkynylated 3H-pyrrolo[1,2-a]indol-3-ones through rhodium-catalyzed C-H alkenylation/DG migration and [3+2] annulation, respectively. This protocol features rare directing group migration in 1,3-diyne-involved C-H activation, excellent regio- and stereoselectivity, excellent monofunctionalization over difunctionalization, broad substrate scope, moderate to high yields, good functional group compatibility, and mild redox-neutral conditions.

Design and Applications of a SO2 Surrogate in Palladium-Catalyzed Direct Aminosulfonylation between Aryl Iodides and Amines.

A new SO2 surrogate is reported that is cheap, bench-stable, and can be accessed in just two steps from bulk chemicals. Essentially complete SO2 release is achieved in 5 minutes. Eight established sulfonylation reactions proceeded smoothly by ex situ formation of SO2 by utilizing a two-chamber system in combination with the SO2 surrogate. Furthermore, we report the first direct aminosulfonylation between aryl iodides and amines. Broad functional group tolerance is demonstrated, and the method is applicable to pharmaceutically relevant substrates, including heterocyclic substrates.

DGT methodology is more sensitive than conventional extraction strategies in assessing amendment-induced soil cadmium availability to rice.

Using diffusive gradients in thin films (DGT) is a recently developed alternative method of rapidly evaluating the bioavailability of metals in soil. However, the method has found only limited application in systematic assessment of the bioavailability of cadmium (Cd) in red limestone paddy soils treated with different soil amendments. Of the four methods compared for estimating Cd content of rice grains from plants grown in such soils of central China treated with eleven different soil amendments in pot culture, Cd content of DGT-labile soil was significantly correlated to Cd concentrations in brown rice (R = 0.447, p < 0.01). The other three methods involved CaCl2, diethylenetriaminepentaacetic acid (DTPA), or NH4NO3. Some other properties of soil, such as pH, redox potential, content of dissolved organic matter, and cation exchange capacity were also determined. A simple algorithm developed to evaluate the sensitivity of the four methods also confirmed DGT as the most efficient method to predict the bioavailability of Cd in red limestone paddy soils.

Rhodium(III)-Catalyzed C-H Alkenylation/Directing Group Migration for the Regio- and Stereoselective Synthesis of Tetrasubstituted Alkenes.

An efficient Rh(III)-catalyzed C-H alkenylation/directing group migration cascade between indoles and alkynes for the assembly of tetrasubstituted alkenes is reported. The carbamoyl directing group migrates to the carbon of the alkene moiety of the products through rare Rh-catalyzed C-N bond cleavage after the C-H alkenylation step and thus acts as an internal amidation reagent. This protocol shows broad substrate scope, excellent regio/stereoselectivity, and good to excellent yields.

Nickel-Catalyzed Intramolecular Desulfitative C-N Coupling: A Synthesis of Aromatic Amines.

A nickel-catalyzed intramolecular C-N coupling reaction via SO2 extrusion is presented. The use of a catalytic amount of BPh3 allows the transformation to take place under much milder conditions (60 °C) than previously reported C-N coupling reactions by CO or CO2 extrusion (160-180 °C). In addition, this method displays good functional group tolerance and versatility, as it can be applied to the synthesis of dialkyl aryl amines, alkyl diaryl amines, and triaryl amines. The robustness of the desulfitative C-N coupling is demonstrated by three high-yielding gram-scale reactions.

Green and Facile Assembly of Diverse Fused N-Heterocycles Using Gold-Catalyzed Cascade Reactions in Water.

The present study describes an AuPPh3Cl/AgSbF6-catalyzed cascade reaction between amine nucleophiles and alkynoic acids in water. This process proceeds in high step economy with water as the sole coproduct, and leads to the generation of two rings, together with the formation of three new bonds in a single operation. This green cascade process exhibits valuable features such as low catalyst loading, good to excellent yields, high efficiency in bond formation, excellent selectivity, great tolerance of functional groups, and extraordinarily broad substrate scope. In addition, this is the first example of the generation of an indole/thiophene/pyrrole/pyridine/naphthalene/benzene-fused N-heterocycle library through gold catalysis in water from readily available materials. Notably, the discovery of antibacterial molecules from this library demonstrates its high quality and potential for the identification of active pharmaceutical ingredients.

Recent Advances in the Addition of Amide/Sulfonamide Bonds to Alkynes.

The addition of amide/sulfonamide bonds to alkynes is not only one of the most important strategies for the direct functionalization of carbon⁻carbon triple bonds, but also a powerful tool for the downstream transformations of amides/sulfonamides. The present review provides a comprehensive summary of amide/sulfonamide bond addition to alkynes, including direct and metal-free aminoacylation, based-promoted aminoacylation, transition-metal-catalyzed aminoacylation, organocatalytic aminoacylation and transition-metal-catalyzed aminosulfonylation of alkynes up to December 2018. The reaction conditions, regio- and stereoselectivities, and mechanisms are discussed and summarized in detail.

FeCl3∙6H2O/TMSBr-Catalyzed Rapid Synthesis of Dihydropyrimidinones and Dihydropyrimidinethiones under Microwave Irradiation.

An efficient and practical protocol has been developed to synthesize dihydropyrimidinones and dihydropyrimidinethiones through FeCl3∙6H2O/TMSBr-catalyzed three-component cyclocondensation under microwave irradiation. This approach features high yields, broad substrate scope, short reaction time, mild reaction conditions, operational simplicity and easy work-up, thus affording a versatile method for the synthesis of dihydropyrimidinones and dihydropyrimidinethiones.