Preparation of chiral alpha-oxy-[2H1]methyllithiums of 99% ee and determination of their configurational stability

(Tributylstannyl)methyl 2,2,6,6-tetramethylpiperidine-1-carboxylate was metalated with t-BuLi/TMEDA at -78 degrees C and borylated with the mixed borate derived from (R,R)-1,2-dicyclohexylethane-1,2-diol and t-butanol to give diastereomeric boronates 31/32 in equal amounts. Boronates 31 and 32 were reduced with LiBEt3D and then oxidized with basic H2O2 to give (S)- and (R)-tributylstannyl-[1-2H1]methanol of 99% ee, respectively. Treatment of their respective phosphates with n-BuLi at -78 and 0 degrees C gave microscopically configurationally stable phosphinyloxy-substituted [2H1]methyllithiums, which rearranged to hydroxy-[1-2H1]methylphosphonates of ee > 98% (phosphate-phosphonate rearrangement). The N,N-diisopropylcarbamates of the enantiomeric tributylstannyl-[1-2H1]methanols were transmetalated to give carbamoyloxy-substituted chiral [2H1]methyllithiums, which were macroscopically configurationally stable for prolonged periods of time (up to 3 h, ee still 99%) at -78 degrees C, deduced from trapping experiments with benzaldehyde. The chemical stability of these methyllithiums ended at -50 degrees C. The stereochemistry of the monoprotected and monodeuterated 1-phenylethane-1,2-diols obtained was secured by spectroscopic comparison of their Mosher esters with that of all four stereoisomeric 1-phenyl-[1-2H1]ethane-1,2-diols synthesized independently. Furthermore, the configurations of the boronates and the chiral methyllithiums derived from them were deduced from a single-crystal X-ray structure analysis of a carbamate in which the tributylstannyl group had been replaced by the [(1R)-menthyl]dimethylstannyl group.     

High-performance polymer solar cells with >13% efficiency

正In the last three years,polymer solar cells(PSCs)based on ntype organic semiconductor(n-OS)acceptor have become the focus of attention and made great progress.In 2017,the power conversion efficiencies(PCEs)have been boosted to~13%for PSCs with single-junction and~14%for PSCs     

High-performance polymer solar cells with >10% efficiency

<正>Polymer solar cells(PSCs)with bulky heterojunction structure have attracted considerable attention due to their advantages in making flexible,light weight and large area solar cell panels through the low cost roll-to-roll printing technologies.In the past decades,tremendous efforts have been devoted to developing new materials and device fabrication methods to improve the power conversion efficien-     

Quinoidal Azaacenes: 99 % Diradical Character

Quinoidal azaacenes with almost pure diradical character (y=0.95 to y=0.99) were synthesized. All compounds exhibit paramagnetic behavior investigated by EPR and NMR spectroscopy, and SQUID measurements, revealing thermally populated triplet states with an extremely low‐energy gap ΔE_ST′ of 0.58 to 1.0 kcal mol^?1. The species are persistent in solution (half‐life≈14–21 h) and in the solid state they are stable for weeks.     

Two-Step Synthesis of trans-2-Arylcyclopropane Carboxylates with 98–100 % ee by the Use of a Phosphazene Base

Only the axial diastereomer of sulfonium salts 2 are formed upon alkylation of 1 . Deprotonation of 2 results in ylides, which allow the highly enantioselective cyclopropanation of Michael systems. The chiral auxiliary 1 is recovered and can be reused.     

Coupling polymerization of monofunctional allene derivatives with malonates bearing aryl halides moieties via π-allylpalladium complex

A novel polymerization method of allene derivatives with nucleophiles bearing aryl halide moieties (A-B type) is described. By the polymerization of hexylallene with malonates bearing an aryl iodide part, polymers consisting both of internal and exomethylene (exo) double bonds were obtained by mean of the coupling reaction of three different components in high yields. On the other hand, a polymer obtained from phenylallene was selectively composed of internal double bonds (E and Z). By the reaction of hexylallene with a malonate bearing two aryl halide moieties (A-B₂ type), a multibranched polymer was also obtained. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2097–2103, 1997     

Active and passive transport of amino acid derivatives via metal complex carriers

A new class of carrier, lipophilic copper complex, mediated active and passive transport of a variety of amino acid derivatives as carboxylate anion.     

Rhodium‐Catalyzed Stereoselective Amination of Thioethers with N‐Mesyloxycarbamates: DMAP and Bis(DMAP)CH2Cl2 as Key Additives

A stereoselective Rh‐catalyzed intermolecular amination of thioethers using a readily available chiral N‐mesyloxycarbamate to produce sulfilimines in excellent yields and diastereomeric ratio is described. A catalytic mixture of 4‐dimethylaminopyridine (DMAP) and bis(DMAP)CH₂Cl₂ proved pivotal in achieving high selectivity. The X‐ray crystal structure of the (DMAP)₂?[Rh₂{(S)‐nttl}₄] complex was obtained and mechanistic studies suggested a Rh^II‐Rh^III complex as the catalytically active species.     

Stereoselective acylation of 20-(S)-camptothecin with amino acid derivatives using scandium triflate/DMAP

Facile esterification of the hindered 3° alcohol 20-(S)-camptothecin with Boc protected chiral amino acids or derivatives under mild conditions has been achieved in high yield using the combination of Sc(OTf)₃ and DMAP. The isomeric purity of the product was maintained under these conditions.     

Facile microwave-assisted synthesis of bis-pyrazol pyrimidine derivatives via an <Emphasis Type="Italic">N</Emphasis>-alkylation reaction

Abstract  

We present herein a new and efficient method for synthesis of bis-pyrazol pyrimidine derivatives by N-alkylation using a microwave-assisted synthetic process. Two new compounds, N-(4,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)methyl nicotinonitrile and 2,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)-4-methyl nicotinonitrile, were synthesized by the N-alkylation reaction. The novel compounds were characterized by Fourier transform infrared spectrometry, ultraviolet spectroscopy, elemental analysis, and nuclear magnetic resonance spectroscopy, etc. The microwave-assisted procedures have noteworthy advantages in terms of thermal efficiency over those carried out by conventional heating methods.     

α‐Chloroalkylmagnesium Reagents of >90 % ee by Sulfoxide/Magnesium Exchange

Not only for ligand exchange at sulfoxides can the sulfoxide/magnesium exchange reaction be used, but it also provides a possibility to generate Grignard reagents in way that avoids metallic magnesium and thus radical processes. Therefore, enantiomerically pure Grignard reagents can be obtained from the corresponding sulfoxides [Eq. (a)].     

Synthesis of latonduine derivatives via intramolecular Heck reaction

The synthesis of indole ring-fused benzazepinone series as latonduine derivatives has been developed via an intramolecular Heck reaction. The scope has been enlarged not only to indole moiety but also to pyrrolo and benzo[b]thiophene nuclei. Several derivatives prepared have been evaluated in vitro for their antiproliferative activities on breast cancer cell lines. Some of them showed promising cytotoxic activities.     

Preparation,characterization and biodistribution of the <Superscript>99m</Superscript>Tc-salicylidenediamine-N-dione complex

A tetradentate set of N₂O₂ salicylaldehyde-amine-N-dione Schiff base was prepared by condensation with salicylaldehyde, ethylenediamine, 2,4-dione and reduction with NaBH₄. The ligand system was characterized by ¹H-NMR and FT-IR spectroscopy and HPLC. Radiolabeling studies of the ^99mTc-complex were performed using stannous ions as the reducing agent. The purity of the complex was determined by ascending solvent system on paper chromatography and instant thin-layer chromatography (ITLC). The yield of the complex was >90%. Biodistribution of the ^99mTc-complex of the precursor was studied in rabbits. A significant uptake and retention of injected activity was observed in the liver and cleared through the bladder. A faint activity was also observed in kidneys. These results indicate that the proposed system may be suitable for development of a liver/spleen imaging agent for future clinical applications.     

Synthesis and characterization of quinoline derivatives via the Friedländer reaction

A rapid and efficient method for the synthesis of various poly-substituted quinolines has been developed via the Friedländer condensation of 2-aminoarylaldehyde with a carbonyl compound containing a reactive α-methylene group in the presence of sodium ethoxide (10 mol %). The new tetrahydroacridine derivatives and 11H-indeno[1,2-b]quinolines were synthesized in high yield with sodium ethoxide as a catalyst via the Friedländer reaction. The conditions of reaction were discussed and the possible reaction mechanism was proposed.