Synthesis of enantiomerically pure vinylcyclopropylboronic esters via cross-metathesis

The potent antibiotic ambruticin caused us to investigate two new aspects of cyclopropylboronic ester chemistry: we established the analytical basics for all 1,2,3-trisubstituted diastereoisomers as well as the cross-metathesis as a tool to synthesise vinylcyclopropylboronic esters.     

Rhodium catalyzed tandem Diels-Alder/hydrolysis reactions of 2-boron-substituted 1,3-dienes

2-Boron substituted 1,3-dienes have been prepared and used in preliminary experiments to demonstrate that it is possible to effect rhodium catalyzed Diels-Alder/hydrolysis tandem reactions.     

Stereoselective construction of azepine-containing bridged scaffolds via organocata-lytic bicyclization of yne-allenone esters with nitrones

A new organocatalytic double annulation cascade involving scission/recombination of N-O bonds of nitrones is reported for the first time, and used to produce a range of hitherto unprecedented tricyclic bridged-fused benzo[d]azepines bearing three stereogenic centers with moderate to good yields and complete diastereoselectivity. A quinine-catalyzed reaction of yne?allenone esters with nitrones worked well and provided a convergent and regioselective pathway to access these three-dimensional scaffolds from the planar conjugated system. Density functional theory (DFT) calculations have been applied to understand the key process for forming diradical intermediates.     

Synthesis and reaction of secondary and primary diorganozinc reagents using a boron–zinc exchange reaction: A useful method for the stereo- and regioselective formation of new carbon---carbon bonds

Applications of the boron–zinc exchange reaction to make new carbon---carbon bonds are reviewed. Functionalized chiral secondary alkylzinc reagents can be prepared by this exchange reaction and allows to perform formal enantioselective Michael-additions with umpolung of reactivity. The scope of substrate controlled diastereoselective hydroborations can be considerably enhanced by this methodology. A chemoselective approach to difunctionalized arylsilanes is also described.     

Direct vinylation of glucose derivatives with acetylene

Vinyl ethers, promising chiral carbohydrate synthons, have been synthesized by the addition of glucose acetals (1,2:5,6-di-O-isopropylidene-α-d-glucofuranose, methyl 4,6-O-benzylidene-α-d-glucopyranoside, 1,2-O-cyclohexylidene-α-d-glucofuranose, methyl α-d-glucopyranoside) to acetylene under atmospheric and elevated pressures in an autoclave in the presence of superbase catalytic systems (KOH-DMSO, t-BuOK-DMSO). The complete vinylation of 1,2:5,6-di-O-isopropylidene-α-d-glucofuranose and methyl α-d-glucopyranoside has been realized under elevated pressure of acetylene in the system KOH-THF as well.     

A Bio-Inspired Trehalose Additive for Reversible Zinc Anodes with Improved Stability and Kinetics

The moderate reversibility of Zn anodes, as a long-standing challenge in aqueous zinc-ion batteries, promotes the exploration of suitable electrolyte additives continuously. It is crucial to establish the absolute predominance of smooth deposition within multiple interfacial reactions for stable zinc anodes, including suppressing side parasitic reactions and facilitating Zn plating process. Trehalose catches our attention due to the reported mechanisms in sustaining biological stabilization. In this work, the inter-disciplinary application of trehalose is reported in the electrolyte modification for the first time. The pivotal roles of trehalose in suppressed hydrogen evolution and accelerated Zn deposition have been investigated based on the principles of thermodynamics as well as reaction kinetics. The electrodeposit changes from random accumulation of flakes to dense bulk with (002)-plane exposure due to the unlocked crystal-face oriented deposition with trehalose addition. As a result, the highly reversible Zn anode is obtained, exhibiting a high average CE of 99.8 % in the Zn/Cu cell and stable cycling over 1500 h under 9.0 % depth of discharge in the Zn symmetric cell. The designing principles and mechanism analysis in this study could serve as a source of inspiration in exploring novel additives for advanced Zn anodes.     

Indium triflate-catalyzed vinylation of beta-ketoesters with acetylene gas

[reaction: see text]. An In(OTf)(3)-catalyzed addition of a beta-ketoester to acetylene in the presence of molecular sieves produces a alpha-vinylated ketoester in good to excellent yield. The vinylation reaction proceeds without any loss of elements in starting molecules under solvent-free conditions and allows the use of welding-grade acetylene, providing a practical method for synthetic utilization of acetylene gas.     

Synthesis of alpha-trifluoromethyl-beta-lactams and esters of beta-amino acids via 1,3-dipolar cycloaddition of nitrones to fluoroalkenes

Nitrones derived from aromatic or aliphatic aldehydes or ketones react with hexafluoropropene (HFP) or 2H-pentafluoropropene (PFP) to give the respective fluorinated isoxazolidine derivatives in good yields with complete regioselectivity and moderate diastereoselectivity. Catalytic hydrogenolysis of the N-O bond under ambient pressure and temperature leads to fluorides of beta-amino acids that undergo cyclization to alpha-trifluoromethylated beta-lactams or, under acidic conditions, form esters of alpha-trifluoromethylated beta-amino acids.     

Rhodium-catalyzed cross-coupling of allyl alcohols with aryl- and vinylboronic acids in ionic liquids

[reaction: see text] The direct coupling of aryl- and vinylboronic acids with allylic alcohols has been achieved in ionic liquids using a rhodium catalyst.     

Regioselective vinylation of kojic acid using acetylenic esters in the presence of triphenylphosphine or tert-butyl isocyanide

Abstract  

The 1:1 reactive intermediates generated by addition of tert-butyl isocyanide or triphenylphosphine to acetylenic esters were trapped by kojic acid to yield O-vinylated and C-vinylated kojic acid, respectively.     

Asymmetric 1,3-dipolar cycloaddition of nitrile oxides with optically active vinylboronic ester

Pinanyldioxy styrylboronic ester (1) was employed for asymmetric 1,3-dipolar cycloaddition with nitrile oxides, optically active △2-isoxazolines (3) or 4-hydroxy-△2-isoxazolines (4) were obtained. The effect of different bases on the selectivity of the cycloaddition reaction was studied.     

N, O-ligand accelerated zinc-catalyzed transesterification of alcohols with vinyl esters

N-Phenyldiethanolamine (1f) is an efficient ligand for zinc-catalyzed transesterification of alcohols with vinyl acetate (R³ = Me) at room temperature. In the case of using other vinyl esters (R³ = Et, n-Pr, Ph), the corresponding products were easily obtained in the presence of pyridine-type ligand 2 instead of aminoalcohol 1f.     

The cycloaddition of nitrones with homochiral cyclopropanes

The cycloaddition of nitrones and enantiomerically pure cyclopropane-1,1-dicarboxylates is examined. Transfer of optical activity to the adduct is dictated by thermal reaction conditions and nature of cyclopropane substitution. Optically active 2-substituted cyclopropane-1,1-dicarboxylates are shown to racemize under typical reaction conditions, providing evidence for a zwitterionic ring-opened intermediate.     

Reactions of nitrones with di- and tetrahydropyrans

N-(Benzylidene)- and N-(2-phenylamino-2-oxoethylidene)aniline N-oxides add stereospecifically to the double bond in 4-methylene- and 4-acryloylamino-4-methyltetrahydropyrans to give substituted isoxazolidines. The use of 4-methyl-5-arylamino- and 4-arylaminomethyl-5,6-dihydro-2H-pyrans for the synthesis of novel N-oxides has given tricyclic adducts resulting from intramolecular cyclization of the required compounds.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1113–1116, August, 1990.     

Transmetallation of Bis(6-diphenylphosphinoacenaphth-5-yl)-Mercury and -Tributyltin with Precious Metal Chlorides

The reaction of bis(6-diphenylphosphinoacenapht-5yl)mercury, (6-Ph₂P-Ace-5-)₂Hg, with [(CO)₂RhCl]₂ and PtCl₂ proceeded with extrusion of mercury / mercury(I) chloride and provided the octahedral rhodium and platinum complexes (6-Ph₂P-Ace-5-)₂Rh(CO)Cl and (6-Ph₂P-Ace-5-)₂PtCl₂, respectively. The reaction of the (6-diphenylphosphinoacenapht-5yl)stannane 6-Ph₂P-Ace-5-SnBu₃ with PdCl₂ gave rise to tributyltin chloride and a dimeric arylpalladium chloride [(6-Ph₂P-Ace-5-)PdCl]₂ with a planar Pd₂Cl₂ core. Together with the previously known gold(III) complex cis- and trans-[R₂Au][Cl], the newly prepared compounds were investigated by DFT calculations. The fully optimized gas-phase structure of [(6-Ph₂P-Ace-5-)PdCl]₂ gives rise to a bend Pd₂Cl₂ core featuring a Pd ··· Pd palladophilic interaction. The bonding situation was studied using a set of real-space bonding indicators (RSBIs) derived from the methods Atoms-In-Molecules (AIM), Electron Localizability Indicator (ELI-D) and Non-Covalent Interaction (NCI) index.     

An Improved Method for the Synthesis of N-Phenoxyacetylribonucleosides

N-phenoxyacetylribonucleosides were prepared efficiently from the reaction of ribonucleosides with phenoxyacetylchloride and 1,2,4-triazole(for adenosine and cytidine) or 1-hydroxybenzotriazole (for guanosine).     

Electroanalytical Determination of Zinc in Human Blood Facilitated by Acoustically Assisted Double Extraction

The electroanalytical determination of zinc in human blood via an acoustically assisted double extraction technique is reported. First zinc(II) is rapidly extracted from diluted blood via complexation with diphenylthiocarbazone in chloroform through acoustic emulsification of the two phases. After insonation the bulk phases reform and the metal is back extracted by emulsifying with electrochemically clean aqueous acid and the zinc quantified via anodic stripping voltammetry, giving close agreement to the blind independent AAS analysis. The double extraction method is effective since species that otherwise interfere with the direct ASV determination either remain in the initial aqueous phase, or are transferred to the organic phase, but are unlikely to be doubly transferred so producing a ‘clean’ final aqueous medium for ASV.     

Synthesis of alkyl nitrones by reaction of aldehyde and ketone oximes with α,β-unstaturated esters in the presence of Lewis acid

Reactions of pyridinecarbaldehyde oximes, methyl pyridyl ketone oximes, furfural oxime, cinnamaldehyde oxime, and crotonaldehyde oxime with acrylic and methacrylic acid esters in the presence of a Lewis acid catalyst at room temperature followed the conjugate addition pattern to give the corresponding alkyl nitrones in good yield. The best yields were obtained using a 1: 1 mixture of CdI₂ and BF₃ · Bu₂O as catalyst. Published in Russian in Zhurnal Organicheskoi Khimii, 2009, Vol. 45, No. 4, pp. 605–609. The text was submitted by the authors in English.