Transition-metal-free coupling reactions involving gem‑diborylalkanes

Due to the increasing demand for the sustainability of modern organic chemistry, the development of green and powerful methods for C-C and C-B bond formation is highly desired. Among them, the transition-metal-free coupling reactions of gem‑diborylalkanes emerge as one valuable tool for organic chemists in the last decade. The review covers selected representative examples. A comparison of these reactions with transition-metal-catalyzed reactions is provided. The recent example of α-boryl radical formation from gem‑diborylalkanes is also briefly discussed.     

Stereospecific formation of 7,8β-dihydroanalogs at the reduction of ponasterone acetonide with lithium in liquid ammonia

The reduction of ponasterone A diacetonide with lithium in liquid ammonia stereospecifically led to 7,8β-dihydroanalogs of 5α- and 5β-epimers of ponasterone A and 7,8β-dihydro-6α-hydroxy derivative. 7,8β-Dihydroponasterone A, phytoecdysteroid from the needles of Japanise yew Taxus cuspidata, and its 5α-epimer were synthesized.     

Correction to: Research progress of nano‑silicon‑based materials and silicon‑carbon composite anode materials for lithium‑ion batteries

Journal of Solid State Electrochemistry - In order to solve the energy crisis, energy storage technology needs to be continuously developed. As an energy storage device, the battery is more widely...     

Quasiemulsion-templated formation of α-Fe2O3 hollow spheres with enhanced lithium storage properties

α-Fe(2)O(3) hollow spheres with sheet-like subunits are synthesized by a facile quasiemulsion-templated method. Glycerol is dispersed in water to form oil-in-water quasiemulsion microdroplets, which serve as soft templates for the deposition of the α-Fe(2)O(3) shell. When tested as anode materials for lithium-ion batteries, these α-Fe(2)O(3) hollow spheres manifest greatly enhanced Li storage properties.     

Stereoselective Synthesis of C-Glycosides by Suzuki Cross-coupling Reaction

Carbohydrates and their conjugates have been recognized to play a wide variety of metabolic roles in numerous biological processes.[1] Various modified sugars and analogues have been recently synthesized for further investigation of glycosidase reactions and for the development of specific glycosidase inhibitors.[2] As one of the most important carbohydrate mimics, C-glycosides have attracted great attention due to their stability to chemical or enzymatic hydrolysis of the glycosidic linkage. A number of methodologies for the preparation of C-glycosides have been extensively investigated.[3] We have recently reported the syntheses of novel C-glycosyl amino acids and amino-C-disaccharides possessing a ketose form via the stereoselective 1,3-dipolar cycloaddition of exo-methylenesugars (1) and nitrones.[4,5] As a continuation of our research on the synthesis of C-glycosides using exo-methylenesugar as the precursor, we wish to describe here a stereoselective synthesis of C-glycosides by Suzuki cross-coupling reaction.     

Synthesis of EPR-g-styrene by anionic coupling technique

Ethylene-propylene rubber (EPR) graft copolymers were prepared successfully by anionic coupling technique between chlorinated EPR (Cl-EPR) and living anionic polystyrene chain.The EPR-g-styrene was characterized by hydrogen nuclear magnetic resonance (~1H NMR) and gel penetration chromatogram (GPC).     

Carbon-carbon bond formation by radical addition of α-trifluoromethylacrylate with cyclic ethers

The radical addition reactivity of tert-butyl α-trifluoromethylacrylate (CH₂C(CF₃)COOC(CH₃)₃) (BFMA) with cyclic ethers was investigated in order to compare to that of perfluoroisopropenyl ester. One to one addition compound of BFMA with tetrahydrofuran (THF) was produced in fairy high yields in the presence of 2,2′-azobisisobutyronitrile, benzoyl peroxide or di-tert-butyl peroxide to give 2-substituted THF derivative. Time-conversion investigation showed much higher reactivity of BFMA compared to that of 2-benzoxypentafluoropropene [CF₂C(CF₃)OCOC₆H₅]. Radical additions of BFMA with 1,4-dioxane, 1,3-dioxolane and tetrahydropyran were also examined to afford corresponding 1:1 addition products in fairly high yields by achieving carbon-carbon bond formation. It is then concluded that no interconversion of fluoroalkylcarbon radical and hydrocarbon radical may take place in the reaction system of BFMA which possesses two less fluorines in the vinyl group compared to 2-benzoxypentafluoropropene. The method may be a facile way to prepare trifluoromethyl-substituted organic compounds accompanied by the formation of carbon-carbon bonds by the aid of fluorine atoms.     

Stereoselective formation of (Z)-2-fluoroalkenoates via Julia–Kocienski reaction of aldehydes with pyrimidinyl-fluorosulfones

The selective synthesis of fluoroalkenoates is reported from a pyrimidinyl fluorosulfone. This sulfone allowed the preparation of Z-fluoroalkenoates with very high stereoselectivity from both aromatic and aliphatic aldehydes. The nature of the heterocycle on the course of the Julia–Kocienski reaction is discussed.     

Stereoselective synthesis of benzyl-protected β-galactosides by propionitrile-mediated glycosylation

β-Selective galactosylation was studied using a series of 2-O-benzylated phenyl 1-thio-galactosides and glycosyl acceptors in propionitrile with BSP-TTBP-Tf₂O. The glycosylation enabled us to synthesize useful precursors of N-acetyllactosamine and core 1 O-glycoserine derivatives in a highly convergent manner.     

Stereoselective Synthesis of 1,1′-Disaccharides by Organoboron Catalysis

The highly stereoselective synthesis of 1,1′-disaccharides was achieved by using 1,2-dihydroxyglycosyl acceptors and glycosyl donors in the presence of a tricyclic borinic acid catalyst. In this reaction, the complexation of the diols and the catalyst is crucial for the activation of glycosyl donors, as well as for the 1,2-cis-configuration of the products. The anomeric stereochemistry of the glycosyl donor depends on the employed glycosyl donor. Applications of the produced 1,1′-disaccharides are also described.     

Stereoselective Synthesis of Piperamide Alkaloids by Modified Ramberg-Baecklund Reaction

A convenient and rapid approach for the synthesis ofpiperamide alkaloids la ～ h by the recently developed one-flask Ramberg-Baecklund reaction was described. The synthesis of le was reported for the first time.     

Reaction of α-carbanions of lithium acylates with 1,2-dibromoethane

The reaction of 1,2-dibromoethane with α-carbanions of lithium acylates generated from acetic, butyric, isobutyric, and capronic acids with lithium diisopropylamide has been studied. Anion-radical and anionic pathways of the products formation have been discussed.     

Ring-opening of cyclic ethers with carbon–carbon bond formation by Grignard reagents

The ring-opening of cyclic ethers with concomitant C–C bond formation was studied with a number of Grignard reagents. The transformation was performed in a sealed vial by heating to ∼160 °C in an aluminum block or at 180 °C in a microwave oven. Good yields of the product alcohols were obtained with allyl- and benzylmagnesium halides when the ether was tetrahydrofuran or 3,3-dimethyloxetane. Lower yields were obtained with substituted tetrahydrofurans while no ring-opening was observed with tetrahydropyran. Only highly reactive allyl and benzyl Grignard reagents participated in the transformation while no reaction occurred with other alkylmagnesium halides.     

Selective formation of unsymmetric ureas by selenium-catalyzed oxidative–reductive carbonylation with CO

A series of unsymmetric ureas containing substituted groups have been synthesized via selenium-catalyzed selective oxidative–reductive carbonylation of amines and nitro compounds with CO instead of phosgene in one-pot reaction. These catalytic reactions are important from both synthetic and industrial points of view, because not only the reactions can be proceeded with high selectivity of higher than 99% towards desired unsymmetric ureas, but also there exists a phase-transfer process of the selenium catalyst in the reaction, so that the after-treatment of the catalysts and products from the reaction systems can be easily separated by simple phase separation.     

Rhodium-catalyzed coupling of α-lactams with indole derivatives

We report herein a method that allows for the formation of a C–N bond between the C–3 carbon of α-lactams and the nitrogen atom of indoles. A general procedure for the coupling of indoles and α-lactams in only 25 min with high yield is reported. The scope of the reaction was extended by the development of a method for the in situ generation of less stable phenyl-substituted α-lactams. The developed method provides an atom-economical method for the formation of substituted α-amino amides that are found in a variety of biologically-active compounds.     

Stereoselective Synthesis of δ-Selanyl Allylic Alcohols by Hydrozirconation of Propargyl Selenides

Hydrozirconation of propargyl selenides afford(E)-3-selanyl vinylzirconocenes chlorides 2.Intermediates 2 reacted with aldehydes to obtain δ-selanyl allylic alcohols.     

Enhanced lithium intercalation and conduction in LiαFeTaxOyCz films by the addition of lithium oxides with an atmospheric pressure plasma jet

Journal of Solid State Electrochemistry - An enhancement of lithium ionic intercalation and conduction performance of lithiated-organo-iron-tantalum oxide (LiαFeTaxOyCz) films has been...     

Stereoselective Synthesis of δd-Selanyl Allylic Alcohols by Hydrozirconation of Propargyl Selenides

Functionality-bearingallylicalcoholsarethevitalstructureunitsofbiologicallyactivecompounds1,2.Allylicselenidesareimportantintermediatesinorganicsynthesis3,4.Soregio-andstereoselectivesynthesisofd-selanylallylicalcoholwhichcombinetheallylicalcoholandallylicselenideunitstogetherisofinterestinorganicsynthesis.Hydrozirconationhasemergedasauniquehydrometallationwithsomeattractivefeatures5,6.Recentlywehavereportedthestereoselectivesynthesisofa-heteroatomsubstitutedallylicalcoholsbyhydrozirconationof…     

Complex formation of crown ethers with α-amino acids: Estimation by NMR spectroscopy

Complex formation of 18-crown-6 and dibenzo crowns with glycine, leucine, and norleucine was studied by NMR spectroscopy. The efficiency of non-valence interactions with participation of different active centers of the host and guest molecules is determined by solvation effects, mutual arrangement of benzene rings in dibenzo crowns, and the presence of bulky aliphatic substituents in the α-amino acid. The complexation of dibenzo crowns with α-amino acids in acid medium involves a system of different non-valence interactions, the most efficient of which are NH ₃ ⁺ ... O hydrogen bond between the ammonium group in the guest molecule and ether oxygen atoms in the host molecule and dipole-dipole interaction between the guest ammonium group and host benzene ring (NH ₃ ⁺ ... Ar). The efficiency of NH ₃ ⁺ ... O hydrogen bonding decreases in going from 18-crown-6 to dibenzo crowns due to distortion of symmetry of the macroring cavity and violation of geometric complementarity of some ether oxygen atoms. The integral efficiency of non-valence interactions in the system dibenzo crown-α-amino acid was estimated on a quantitative level by ¹H NMR relaxation technique.     

Stereochemistry of internucleotide bond formation by the H-phosphonate method. 7. Stereoselective formation of ribonucleoside (RP)- and (SP)-3′-H-phosphonothioate monoesters

Ribonucleoside 3′-H-phosphonothioate monoesters exist in the form of (R_P)- and (S_P)-diastereomers. In order to obtain them in good yields and in high stereochemical purity, stereoselective strategies for their preparation were investigated. For the synthesis of the (R_P)-isomer, a stereoselective sulfhydrolysis of an activated nucleoside H-phosphonate was developed, while the monoesters with an (S_P)-configuration were prepared by asymmetric transformation of diastereomeric mixtures of nucleoside 3′-H-phosphonothioates using either a condensation with 9-fluorenemethanol, followed by β-elimination, or via pivaloylation-hydrolysis reaction sequence. A tentative assignment of the absolute configurations of the obtained diastereomers of 3′-H-phosphonothioate esters was carried out via a stereochemical correlation analysis.