Synthesis of acridinedione derived mono spiro-pyrrolidine/pyrrolizidine derivatives—a facile approach via intermolecular [3+2] cycloaddition reaction

A facile synthesis of acridinedione derived mono spiro-pyrrolidine and pyrrolizidine derivatives has been accomplished by 1,3-dipolar cycloaddition reaction. The O-acryloylacridinediones, as dipolarophiles reacted with azomethine ylide derived from di-/tri-ketones and sec-amino acids to give acridinedione derived mono spiropyrrolidine/pyrrolizidine derivatives in good yield.     

Asymmetric synthesis of chiral bisoxazolines and their use as ligands in metal catalysis

Novel C₂- and C₁-symmetric chiral bisoxazolines with a cyclic backbone have been synthesized in an asymmetric manner starting from meso anhydrides. All synthetic steps are easy to perform and lead to the desired products in good overall yields. Preliminary investigations revealed the applicability of these new compounds as ligands in transfer hydrogenations and various metal-catalyzed enantioselective C–C-bond forming reactions such as cyclopropanations and Diels–Alder reactions.     

Synthesis and application of a new pseudo C2-symmetric tertiary diamine for the enantioselective addition of MeLi to aromatic imines

A new tertiary pseudo C₂-symmetric diamine derived from (1S,2S)-(+)-pseudoephedrine was synthesized and tested in the enantioselective addition of methyllithium on different aromatic imines. A comparative study with a similar C₂-symmetric ligand derived from the cyclohexane diamine showed better reactivity and enantioselectivity up to 91%.     

Comparing propene polymerization with 1-butene polymerization catalyzed by MAO-activated C2- and C1-symmetric zirconocenes: An experimental and computational study on the influence of olefin size on stereoselectivity

Polypropene and poly(1-butene) have been synthesized under very similar experimental conditions with a series of MAO-activated C₂-symmetric and C₁-symmetric ansa-zirconocenes. The C₁-symmetric zirconocenes bearing the bilaterally symmetric fluorenyl or bis(2-methylthieno)cyclopentadienyl ligand connected through a dimethylsilyl bridge to substituted indenyl ligands produce isotactic polybutene of similar or higher molecular mass and with noticeably higher isotacticity, compared to isotactic polypropene prepared with the same catalysts under comparable conditions. Structural and mechanistic reasons for such behavior are discussed on the basis of QM/MM calculations.     

Synthesis by Stille cross-coupling procedure and electrochemical properties of C3-symmetric oligoarylobenzenes

A series of various C3-symmetric molecules were synthesized by Stille cross-coupling procedure. Monomers have been characterized by ¹H NMR, ¹³C NMR. Received oligomers in the process of electropolymerization, containing thienyl, furyl, and EDOT groups provide good conductivity and show stability in common organic solvents such as CHCl₃, toluene, and CH₂Cl₂ and exhibit thermal stability. Electrochemical results suggest that obtained materials can be successfully used in wide scale of organic-electronic devices such as organic light-emitting diodes (OLEDs), organic field-effect transitors (OFETs), and organic solar cells.     

Doubly [SiMe2]-bridged Cs- and C2v-symmetric zirconocene catalysts for propylene polymerization. Synthesis and polymerization characteristics

The C_s- and C_2v-symmetric doubly dimethylsilylene-bridged zirconocene complexes (Me₂Si)₂{η⁵-C₅H₂-4-CHMe₂}{η⁵-C₅H-3,5-(SiMe₃)₂}ZrCl₂, 6a, and (Me₂Si)₂{η⁵-C₅H-3,5-(CHMe₂)₂}₂ZrCl₂, 6b, have been synthesized by reaction of corresponding dilithio ligand salts with ZrCl₄ in CH₂Cl₂. When activated with methyl aluminoxane, C_s-symmetric zirconocene 6a catalyzes the polymerization of propylene (liquid propylene, 0°C) to yield a syndiotactic polymer of Mw=1,000,000 and rrrr%=75.4. By contrast, C_2v-symmetric zirconocene 6b displays a low activity and affords an atactic polymer.     

Synthesis of liquid crystalline materials based on 1,3,5-triphenylbenzene and 2,4,6-triphenyl-1,3,5-s-triazine

C₃-symmetric alkyloxy/aryloxy polyether dendrimers have been synthesized from 1,3,5-triphenylbenzene and 2,4,6-triphenyl-1,3,5-s-triazine and their liquid crystalline properties have been studied. C₃-symmetric derivatives with n-hexyl and n-dodecyl chains at the periphery show mesophase properties when they are complexed with trinitrofluorenone at different temperatures.     

Cerium ammonium nitrate (CAN) for mild and efficient reagent to remove hydroxyethyl units from 2-hydroxyethyl ethers and 2-hydroxyethyl amines

Cerium ammonium nitrate (CAN) removed hydroxyethyl units from 2-hydroxyethyl ethers and 2-hydroxyethyl amines to produce alcohols and amines in good yields. Especially, removal of the 2-hydroxyethyl ethers from C₂-symmetric diols, chiral 2,3-butanediol and chiral hydrobenzoin, was very useful for asymmetric syntheses using C₂-symmetric diols. The reactions using dual abilities of CAN, i.e., the ability for removal of the 2-hydroxyethyl unit and the ability for acetal hydrolysis by a single electron transfer, were also achieved successfully. The reaction conditions were very mild and efficient, and many functional groups, which can be affected under normal conditions, were unaffected during the reaction.     

Olefination of ketenes for the enantioselective synthesis of allenes via an ylide route

Pseudo-C₂-symmetric chiral phosphorus ylide is designed and synthesized for the enantioselective preparation of allenic esters, amides, ketone, and nitrile. Up to 92% ee is achieved.     

Enantioselective copper-catalyzed cyclopropanation of styrene by means of chiral bispidine ligands

Enantiopure C₁- and C₂-symmetric bispidine ligands have been synthesized and screened in the asymmetric copper-catalyzed cyclopropanation of styrene. In order to improve the enantiomeric excesses (ee) of the cyclopropane derivatives, the best performing C₁-symmetric diamine ligand was selected for studies on the reaction conditions. The optimized procedure allowed us to obtain up to 91% ee for the cis-cyclopropane derivative and up to 79% ee for the trans one.     

A simple, novel and convenient method for the synthesis of 1-aminophosphinic acids: synthesis of a novel C2-symmetric phosphinic acid pseudodipeptide

A simple, efficient and novel method has been developed for the synthesis of 1-aminophosphinic acids from simple starting materials. Treatment of aromatic aldehydes with ammonia and hypophosphorus acid gives novel C₂-symmetric 1-aminoarylmethylphosphinic acids. The synthesis of novel C₂-symmetric phosphinic acid pseudodipeptides is also discussed.     

A new pseudo C2-symmetric tertiary diamine for the enantioselective addition of MeLi to aromatic imines

A new tertiary pseudo C₂-symmetric 1,2-diamine derived from (1S,2S)-(+)-pseudoephedrine was synthesized and tested in the enantioselective addition of MeLi to aromatic imines. A comparative study with the analogous C₂-symmetric ligand successfully used previously in the same reaction showed comparable selectivity and better reactivity for this novel diamine.     

Synthesis of novel C2-symmetric and enantiomerically pure bisbenzoxazoles and bisbenzothiazoles derived from l- and d-tartaric acids

Five pairs of novel C₂-symmetric and enantiomerically pure bisbenzoxazoles and a pair of bisbenzothiazoles derived from l- and d-tartaric acids have been synthesized from l- and d-2,3-O-isopropylidenetartaric dichlorides and o-aminophenol derivatives or o-aminothiophenol, respectively, in two- or one-step reactions. The mechanism for the formation of bisbenzoxazoles and bisbenzothiazoles was suggested. The UV and ¹H NMR spectra showed that no coordination between the bisbenzoheterazoles and Cu(I) or Ni(II) cations occurred due to the lack of a sufficiently basic nitrogen donor atom in the benzoheterazole moiety.     

Chiral thiophosphoramide and selenophosphoramide ligands in the Cu(I)-promoted catalytic enantioselective 1,3-dipolar cycloaddition reactions of azomethine ylides and pyrrole-2,5-dione derivatives

Chiral C₂-symmetric diphenylthiophosphoramide ligand L1 prepared from C₂-symmetric (1S,2S)-(−)-1,2-diphenylethylenediamine was found to be a fairly effective chiral ligand for Cu(I)-promoted 1,3-dipolar cycloaddition of imines and pyrrole-2,5-dione derivatives to give the corresponding adducts in moderate enantioselectivities and good yields.     

New C2-symmetric bis(sulfonamide)-cyclohexane-1,2-diamine-RhCp complex and its application in the asymmetric transfer hydrogenation (ATH) of ketones in water

C₂-symmetric bis(sulfonamide) ligands derived from trans-(1R,2R)-cyclohexane-1,2-diamine were synthesized and complexed with [Cp^∗RhCl₂]₂ in situ and used in the ATH of aromatic ketones with aqueous sodium formate as the hydrogen source. The chiral secondary alcohols were obtained with 90-99% enantioselectivity and in 50-100% yield. Reductions in water were faster than those in isopropanol/KOH.     

Enantiospecific synthesis of (−)-muricatacin from l-(+)-tartaric acid

Enantiospecific synthesis of (−)-muricatacin, a bio-active lactone comprising of a 5-hydroxyalkylbutan-4-olide structural component has been achieved from l-(+)-tartaric acid. The key step involves a disteroselective reduction of a C₂-symmetric 1,4-diketone derived from tartaric acid followed by a selective Grignard reagent addition.     

Synthesis of C2-symmetric and unsymmetrically substituted 2,2′-dipyridylamines and crystal structure of a chiral 2,2′-dipyridylamine copper(II) complex

C₂-symmetric and unsymmetrically substituted 2,2′-dipyridylamines have been synthesized by sequential Buchwald-Hartwig aminations of halo-pyridines. The X-ray crystal structure of a copper dichloride complex bearing a C₂-symmetric 2,2′-dipyridylamine reveals details of the binding properties of the ligand and the coordination geometry at the metal center. In preliminary experiments the use of the new nitrogen chelates in asymmetric catalysis has been demonstrated.     

Easily accessible chiral dicyclopentadiene ligands for rhodium-catalyzed enantioselective 1,4-addition reactions

A variety of novel C₁-symmetric chiral diene ligands based on the dicyclopentadiene (DCP) skeleton were easily prepared from commercially available DCP. The application of these diene ligands in the rhodium-catalyzed asymmetric 1,4-addition of arylboronic acids to α,β-unsaturated carbonyl compounds has been examined and excellent enantioselectivities (up to 97% ee) as well as good yields were achieved under mild reaction conditions.     

Synthesis of bis(N-heterocyclic carbene) palladium complexes derived from (S,S)-1,2-bis(1-hydroxypropyl)benzene

New o-xylylene-linked bis(benzimidazolium) salts were synthesized in six-steps from C₂-symmetric chiral 1,4-diol, 1,2-bis(1-hydroxypropyl)benzene, as a starting material. The silver complex of bis(benzimidazol-2-ylidene) was obtained on treatment of bis(benzimidazolium) salt with silver oxide. The reaction of the silver bis-NHC with [PdCl₂(PhCN)₂] afforded the bis-NHC complex of palladium. The X-ray diffraction studies on Pd complexes revealed that these complexes have distorted square planar geometry around the Pd center coordinating the NHC ligand in mutually cis-position. The arene ring of o-xylylene unit hanged over the Pd center and thus these complexes showed C₁-symmetric structures. The variable temperature NMR spectroscopy revealed that these Pd complexes showed fluxional behavior between C₁- and C₂-symmetric structures in solution state.     

Novel chiral C2-symmetric multidentate aminophosphine ligands for use in catalytic asymmetric reduction of ketones

A series of novel chiral C₂-symmetric multidentate aminophosphine ligands have been successfully synthesized by Schiff-base condensation of bis（o-formylphenyl）phenylphosphane and easily available monoprotected（1R,2R）-diaminocyclohexane.The catalytic properties of these ligands were investigated in Ir-catalyzed asymmetric transfer hydrogenation of various aromatic ketones,giving the corresponding optical active alcohols with up to 98%conversion and good ee under mild reaction conditions.