Nickel-Catalyzed Chemoselective Carbomagnesiation for Atroposelective Ring-Opening Difunctionalization.

There is a pressing need for methods that can connect enantioenriched organic compounds with readily accessible building blocks via asymmetric functionalization of unreactive chemical bonds in organic synthesis and medicinal chemistry. Herein, the asymmetric chemoselective cleavage of two unactivated C(Ar)-O bonds in the same molecule is disclosed for the first time through an unusual nickel-catalyzed carbomagnesiation. This reaction facilitates the evolution of a novel atroposelective ring-opening difunctionalization.

Nickel-Catalyzed Enantioconvergent Transformation of Anisole Derivatives via Cleavage of C-OMe Bond.

Herein, a protocol for enantioconvergent transformation of anisole derivatives is disclosed via nickel-catalyzed dynamic kinetic asymmetric cross-coupling of the C(Ar)-OMe bond. Versatile axially chiral heterobiaryls are successfully assembled. Synthetic transformations demonstrate the application potential of this method.

Enantioselective alkylative cross-coupling of unactivated aromatic C-O electrophiles.

Nonpolar alkyl moieties, especially methyl group, are frequently used to modify bioactive molecules during lead optimization in medicinal chemistry. Thus transition-metal catalyzed alkylative cross-coupling reactions by using readily available and environmentally benign C-O electrophiles have been established as powerful tools to install alkyl groups, however, the C(sp)-C(sp) cross-coupling via asymmetric activation of aromatic C-O bond for the synthesis of alkylated chiral compounds remains elusive. Here, we unlock a C(sp)-C(sp) cross-coupling via enantioselective activation of aromatic C-O bond for the efficient synthesis of versatile axially chiral 2-alkyl-2'-hydroxyl-biaryl compounds.

Nickel-Catalyzed Enantioselective Arylative Activation of Aromatic C-O Bond.

The pioneering nickel-catalyzed cross-coupling of C-O electrophiles was unlocked by Wenkert in the 1970s; however, the transition-metal-catalyzed asymmetric activation of aromatic C-O bonds has never been reported. Herein the first enantioselective activation of an aromatic C-O bond is demonstrated via the catalytic arylative ring-opening cross-coupling of diarylfurans. This transformation is facilitated via nickel catalysis in the presence of chiral -heterocyclic carbene ligands, and chiral 2-aryl-2'-hydroxy-1,1'-binaphthyl (ArOBIN) skeletons are delivered axially in high yields with high ee.

Ni-Catalyzed Cross-Coupling of Dimethyl Aryl Amines with Arylboronic Esters under Reductive Conditions.

Herein, we reported a successful Suzuki-Miyaura coupling of dimethyl aryl amines to forge biaryl skeleton via Ni catalysis in the absence of directing groups and preactivation. This transformation proceeded with high efficiency in the presence of magnesium. Preliminary mechanism studies demonstrated dual roles of magnesium: (i) a reductant that reduced Ni(II) species to active Ni(I) catalyst; (ii) a unique promoter that facilitated the Ni(I)/Ni(III) catalytic cycle.

Direct Borylation of Tertiary Anilines via C-N Bond Activation.

The first successful catalytic borylation of unactivated aromatic C-N bonds of tertiary anilines without the preactivation or any directing groups is demonstrated. The reactivity of both N,N-dialkylarylamines and N-arylpyrroles were investigated systematically, and the targeted products were furnished in moderate to good yields. The DFT calculation results indicated that the catalytic cycle is furnished via a five-membered cyclic transition-state due to the steric hindrance of the Ni/NHC catalytic system.

Deoxygenation of Ethers To Form Carbon-Carbon Bonds via Nickel Catalysis.

In this article a successful protocol was developed to construct carbon-carbon bonds by the extrusion of the O atom of ethers via nickel catalysis in the presence of reductants. This methodology is featured as a highly economic route to construct sp-sp C-C bonds through dual C-O activation of ethers with good functional group tolerance.

Practical Cross-Coupling between O-Based Electrophiles and Aryl Bromides via Ni Catalysis.

Cross-coupling of various O-based electrophiles with aryl bromides was developed through Ni-catalyzed C-O activation in the presence of magnesium. Beside carboxylates, carbamates, and ethers, phenols exhibited excellent reactivity under modified conditions. This chemistry was featured as a simple and environmentally benign process with low catalyst loading and easy manipulations.

Cu-Catalyzed Alkynylation of Unactivated C(sp(3))-X Bonds with Terminal Alkynes through Directing Strategy.

In this letter, we report an efficient and concise protocol for Cu-catalyzed cross-coupling of unactivated alkyl halides/peusudohalides with terminal alkynes to afford internal alkynes with the assistance of various amides as directing groups. Different alkyl halides/pseudohalides exhibited excellent reactivities, and the inactivated alkyl chlorides and sulfonates showed better reactivity than bromides/iodides. This is the first successful example to apply alkyl chlorides and sulfonates directly in cross-coupling with terminal alkynes in the absence of any additives.

Exploration of earth-abundant transition metals (Fe, Co, and Ni) as catalysts in unreactive chemical bond activations.

Activation of inert chemical bonds, such as C-H, C-O, C-C, and so on, is a very important area, to which has been drawn much attention by chemists for a long time and which is viewed as one of the most ideal ways to produce valuable chemicals. Under modern chemical bond activation logic, many conventionally viewed "inert" chemical bonds that were intact under traditional conditions can be reconsidered as novel functionalities, which not only avoids the tedious synthetic procedures for prefunctionalizations and the emission of undesirable wastes but also inspires chemists to create novel synthetic strategies in completely different manners. Although activation of "inert" chemical bonds using stoichiometric amounts of transition metals has been reported in the past, much more attractive and challenging catalytic transformations began to blossom decades ago.

Direct cross-coupling of benzyl alcohols to construct diarylmethanes via palladium catalysis.

A direct arylation to furnish diarylmethanes from benzyl alcohols was realized through Pd(PPh3)4-catalyzed Suzuki-Miyaura coupling via benzylic C-O activation in the absence of any additives. The arylation is compatible with various functional groups. This development provides an atom- and step-economic way to approach a diarylmethane scaffold under mild and environmentally benign conditions.

[The response characteristics of TM image reflectance to the arid region of soil moisture].

The response characteristics of TM image to the soil moisture in the Tarim River are the research object. Selected the image spectrum (R), spectrum reciprocal (1/R), the logarithm of reciprocal spectrum lg(1/R) and removal normalized difference vegetation index (R(c)) of four spectral index were selected to establish the soil moisture content prediction model, the variance test was used to validate the model significance, the model accuracy level was divided by the posterior variance examination. The results showed that: the model accuracy of the logarithm of reciprocal spectrum lg(1/R) prediction of soil moisture is the highest, and achieved a good level for the monitoring of soil moisture content (0 - 30 cm).