L-Proline-Catalyzed Knoevenagel Condensation: A Facile,Green Synthesis of (E)-Ethyl 2-Cyano-3-(1H-indol-3-yl)acrylates and (E)-3-(1H-Indol-3-yl)acrylonitriles

L-Proline has been utilized as a novel and ecofriendly catalyst in ethanol medium for the Knoevenagel condensation of indole-3-carboxyaldehydes and their N-methyl derivatives 1(a–e) and 4(a–e) with the active methylene compound, ethyl cyanoacetate (2) to afford substituted (E)-ethyl 2-cyano-3-(1H-indol-3-yl)acrylates 3(a–e) and 5(a–e) respectively. These products were reacted with dimethyl sulfate in the presence of PEG-600 as an efficient and green solvent to afford the corresponding N-mthylated derivatives 5(a–e). These Knoevenagel products react with 5% NaOH, yielding (E)-3-(1H-indol-3-yl)acrylonitriles 6(a–e) and 7(a–e).     

Asymmetric Synthesis of （R）- and （S）-Moprolol

A simple and effective procedure for the enantioselective synthesis of （R）- and （S）-moprolol was described. The key step was the asymmetric synthesis of enantiopure （R）- and （S）-guaifenesin, which were synthesized from enantioenriched （R）-3-chloro-l,2-propanediol and （S）-epichlorohydrin via kinetics of hydrolysis resolution of racemic epichlorohydrin by chiral Salen-Co^Ⅲ complex. The e.e. values of both the optical compounds were above 98%, and the chemical structures of the target compounds were confirmed by ^1H NMR, ^13C NMR, IR, and MS.     

Tin(II) aminoalkoxides and heterobimetallic derivatives: the structures of Sn6(O)4(dmae)4, Sn6(O)4(OEt)4 and [Sn(dmae)2Cd(acac)2]2

Tin(II) methoxide reacts with N,N′‐dimethylaminoethanol (dmaeH) to yield Sn(dmae)₂ ( 1 ) along with small amounts of the hydrolysis product Sn₆(O)₄(dmae)₄ ( 2 ). The geometrically more regular iso‐structural cage Sn₆(O)₄(OEt)₄ ( 3 ) was obtained as the only tractable product isolated from reaction of 2 and Sb(OEt)₃, while 1 reacted with CdX₂ (X = acac, I) to afford Sn(dmae)₂Cd(acac)₂ ( 4 ) and Sn(dmae)₂CdI₂ ( 5 ). The X‐ray structures of 2, 3 and 4 are reported. Decomposition of 4 under aerosol‐assisted chemical vapour deposition conditions leads to amorphous tin oxide films with no detectable cadmium (i.e. ca < 2% cadmium), rather than a stoichiometric Sn:Cd oxide. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis of(+)-(2S, 6S)-trans-α-Irone and of(-)-(2S, 6S)-trans-γ-Irone

A 3:1 mixture of (+)-(2S, 6S)-trans-α-irone ((+)-1) and (?)-(2S, 6S)-trans-γ-irone (?)-2) has been synthesized with ca. 70% e. e. by the ene reaction of (?)-(S)-3 and but-3-yn-2-one.     

The relaxation spectra of nickel(II) and cobalt(II) arginine complexes

The temperature-jump method has been used to determine the nickel(II)- and cobalt(II)-arginine complexation kinetics. In the pH range studied, the neutral form of the ligand, HL, is the attacking, as well as the complexed, ligand species. The reactions reported on are of the type where n = 1, 2, 3 and M is Ni or Co. At 25° and ionic strength 0.1M the association rate constants are: for nickel(II) k₁ = 2.3 × 10³(±20%), k₂ = 2.4 × 10⁴(±20%), k₃ = 3.5 × 10⁴(±40%) M^?1 sec^?1; for cobalt(II) k₁ = 1.5 × 10⁵(±20%), k₂ = 8.7 × 10⁵(±20%), k₃ = 2.0 × 10⁵(±40%) M^?1 sec^?1. Arginine binds to metal ions less well than homologous chelating agents due to the electrostatic repulsion arising from the positively charged terminus of the zwitterion. Kinetically, the effect appears in the association rate constants with nickel reactions more strongly influenced than cobalt.     

Synthese der Stannatetraphospholane (tBuP)4SnR2 (R = tBu,nBu, C6H5) und (tBuP)4Sn(Cl)nBu Molekül- und Kristallstruktur von (tBuP)4Sn(tBu)2

Synthesis of the Stannatetraphospholanes (tBuP)₄SnR₂ (R = tBu, nBu, C₆H₅) and (tBuP)₄Sn(Cl)nBu Molecular and Crystal Structure of (tBuP)₄Sn(tBu)₂ The reaction of the diphosphide K₂[tBuP-(tBuP)₂-PtBu] 4 with the halogenostannanes (tBu)₂SnCl₂, (nBu)₂SnCl₂, (C₆H₅)₂SnCl₂ or nBuSnCl₃ in a molar ratio of 1 : 1 leads via a [4 + 1]-cyclocondensation reaction to the stannatetraphospholanes (tBuP)₄SnR₂ 3 b–3 d and (tBuP)₄Sn(Cl)nBu 3 e , respectively, with the binary 5-membered P₄Sn ring system. 3 b was characterized by a single crystal structure analysis; the 5-membered ring exists in a planar conformation. The compounds 3 b–3 e were identified by NMR and also by mass spectroscopy; the ³¹P{¹H}-NMR spectra of 3 b–3 d showed an AA′MM′ (AA′MM′X), 3 e on the other hand an ABCD (ABCDX) spin system.     

Enantioselective epoxidations of alkenes catalyzed by (salen)Mn(III) in aqueous surfactant systems

An aqueous reaction medium, based on a surfactant solution of diethyltetradecylamine N-oxide (AOE-14), was developed for the enantioselective epoxidation of 1,2-dihydronaphthalene and of various cis-β-alkyl styrenes with increasing hydrophobicity, using bleach as oxidant and the Jacobsen chiral (salen)Mn(III) as catalyst. AOE-14 is able to both solubilize all reactants in water and bind the metal of the salen complex acting as coligand. Its use leads to good yields (>75%) and to ee values ranging from 75% up to 91% even in the case of cis-β-alkyl styrenes where lower cis/trans epoxide ratios are observed. The ratio of surfactant/substrate used is 1:1 or 4:1, much lower than those generally used in the literature.     

The Neutral Complex (NH3)Ag(NCO)

Dissolution of solid AgNCO (silver isocyanate) in aqueous ammonia (25 %) and subsequent crystal growth at T = –9 °C furnished the new ammoniate (NH₃)Ag(NCO) as colorless crystals [P2₁/c (no. 14); a = 4.1817(3) Å, b = 14.445(1) Å, c = 6.1988(5) Å, β = 102.0(4)°, V = 365,6(2) ų; Z = 4]. In the molecular monammine complex, which is only stable at temperatures below T = 0 °C, silver is in a twofold, however, asymmetrical coordination by the isocyanate anion and ammonia. At the reaction conditions applied, AgNCO does not form an ionic diammine species (e.g. [Ag(NH₃)₂]⁺) as known from related silver salts. In this sense, the solvation chemistry of AgNCO exhibits a rarely observed feature.     

Characterization of the functionalization reaction product of poly(styryl)lithium with ethylene oxide

The functionalization reaction of poly(styryl)lithiums (M_n = 1.3–9.9 × 10³) with ethylene oxide in benzene proceeds quantitatively ( > 99%) to produce the corresponding hydroxyethylated polymer as determined by vapor phase osmometry, size exclusion chromatography, end-group titration, thin layer chromatography, and ¹H- and ¹³C-NMR spectroscopy. ¹³C-NMR spectral analysis of the functionalized polystyrene with M_n = 1.3 × 10³ was consistent with addition of only one ethylene oxide unit to poly(styryl)lithium, i.e., no evidence for ethylene oxide oligomerization was observed.     

Synthesis and characterization of soluble,fluorescent poly(arylene ether)s,poly(arylene thioether)s,and poly(arylene sulfone)s containing 1,3,5‐triphenylbenzene segments

The bisphenol 4,4″‐dihydroxy‐5′‐phenyl‐m‐terphenyl ( 4 ), containing a 1,3,5‐triphenylbenzene moiety, was synthesized from a pyrylium salt obtained by the reaction of benzaldehyde with p‐methoxyacetophenone with boron trifluoride etherate as a condensing agent. Polymers were obtained from 4 by a nucleophilic displacement reaction with various activated difluoro monomers and with K₂CO₃ as a base. A series of new poly(arylene ether)s ( 8a – 8f ) were obtained that contained phenyl‐substituted m‐terphenyl segments in the polymer chain. Polymers with inherent viscosities of 0.41–0.99 dL/g were obtained in yields greater than 96%. The polymers were soluble in a variety of organic solvents, including nonpolar solvents such as toluene. Clear, transparent, and flexible films cast from CHCl₃ showed high glass‐transition temperatures (T_g = 198–270 °C) and had excellent thermal stability, as shown by temperatures of 5% weight loss greater than 500 °C. 4 was converted via N,N‐dimethyl‐O‐thiocarbamate into the masked dithiol 4,4″‐bis(N,N′‐dimethyl‐S‐thiocarbamate)‐5′‐phenyl‐m‐terphenyl and was polymerized with activated difluoro compounds in the presence of a mixture of Cs₂CO₃ and CaCO₃ as a base in diphenyl sulfone as a solvent. A series of new poly(arylene thioether)s ( 9a – 9e ) were obtained with T_g values similar to those of 8a – 8e . 9a – 9e were further oxidized into poly(arylene sulfone)s with T_g values 40–80 °C higher than those for 8a – 8e and 9a – 9e . These polymers also had good solubility in organic solvents. A sulfonic acid group was selectively introduced onto the pendent phenyl group of polymers 8a and 8f by reaction with chlorosulfonic acid. The polymers were soluble in dipolar aprotic solvents and formed films via casting from dimethylformamide. Polymers 8a – 8f , 11a , and 11f showed blue and red fluorescence under ultraviolet–visible light with emission maxima at 380–440 nm. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 496–510, 2002; DOI 10.1002/pola.10136     

Effect of Microstructures on the Phase Transition Behavior of P(CL‐GL)‐PEG‐P(CL‐GL) Triblock Copolymer Aqueous Solutions

Amphiphilic poly[(ε‐caprolactone)‐co‐glycolide]‐block‐poly(ethylene glycol)‐block‐poly[(ε‐caprolactone)‐co‐glycolide) [P(CL‐GL)‐PEG‐P(CL‐GL)] triblock copolymers with different average lengths of caproyl sequences (L_CL) were synthesized by ring‐opening polymerization at different temperatures. A 25% aqueous solution of the copolymer with L_CL = 11.0 formed a gel, owing to strong crystallinity‐induced hydrophobicity at low temperature, and underwent a gel‐sol transition (UCST behavior) when the temperature was increased to 40 °C. In contrast, the solution of copolymer with L_CL = 6.7 underwent a sol‐gel transition (LCST behavior) due to micelle aggregation. However, a clear sol‐turbid sol phase transition was observed for the copolymer with more random microstructures (L_CL = 5.2).

     

Synthesis and First Applications of a New Chiral Auxiliary (tert-butyl 2-(tert-butyl)-5,5-dimethyl-4-oxoimidazolidine-1-carboxylate)

Both enantiomers of tert-butyl 2-(tert-butyl)-5,5-dimethyl-4-oxoimidazolidine-1-carboxylate ( 11 ; Bbdmoic) were prepared from L -alanine (Schemes 1 and 2). The parent heterocycle, 2-tert-butyl-5,5-dimethylimidazolidin-4-one ( 12 ; from 2-aminoisobutyramide, H-Aib-NH₂, and pivalaldehyde) was also available in both enantiomeric forms by resolution with O,O′-dibenzoyltartaric acid. The compound (R)- or (S)- 11 was used as an auxiliary, but also as a chiral Aib building block in a dipeptide synthesis. The 3-propanoyl derivative 13 of (R)- 11 was used for the preparation of enantiomerically pure 2-methyl-3-phenylpropanoic acid (enantiomer ratio (e.r.) 99.5:0.5), by benzylation of the Zn-enolate (→ 14 ; Scheme 3). Oxidative coupling of the bis-enolate derived from heptanedioic acid and (S)- 11 (→ 23 ) and methanolysis of the auxiliary gave dimethyl trans-cyclopentane-1,2-dicarboxylate ( 26 ) with an e.r. of 93:7 (Scheme 5, Fig. 5). The 3-(Boc-Gly)-Bbdmoic derivative 29 was doubly deprotonated and, after addition of ZnBr₂ alkylated with alkyl, benzyl, or allyl halides to give the higher amino-acid derivatives with excellent selectivities (e.r. > 99.5:0.5, Schemes 6 and 7). Michael additions of cuprates to [(E)-MeCH?CHCO]-Bbdmoic 36 occurred in high yields, but high diastereoselectivities were only observed with aryl cuprates (diastereoisomer ratio (d.r.) 99:1 for R = Ph, Scheme 8). Finally, 3-(Boc-CH₂)-Bbdmoic 17 was alkylated through the ester Li-enolate with primary and secondary alkyl, allyl, and benzyl halides with diastereoselectivities (ds) ranging from 91 to 98%, giving acetals of Boc-Aib-Xxx-O(t-Bu) dipeptides (Scheme 4). The effectiveness of Bbdmoic is compared with that of other chiral auxiliaries previously used for the same types of transformations.     

XPS analysis (ESCA) of the surface composition of poly(styrene/2-hydroxyethyl methacrylate) microspheres produced by emulsifier-free emulsion polymerization

Polymer microspheres composed of various compositions of styrene and 2-hydroxyethyl methacrylate (HEMA) were produced by batch emulsifier-free emulsion polymerization. The HEMA content at the surface, [HEMA] _s , of the microspheres powdered by freeze-drying was determined by both quantitativeC ^1s /O ^1s analysis andC ^1s peak shape analysis of the x-ray photoelectron spectroscopic spectra. When the HEMA content in the microsphere, [HEMA] _p , was less than about 5 mole%, the [HEMA] _s values determined by the two different methods showed good agreement. At [HEMA]_p above 5 mole %, [HEMA]_s values determined by the first method were about 15 mole % greater than those determined by the second. They both showed a similar tendency with the [HEMA] _s being higher than the [HEMA] _p , e.g., when [HEMA] _p was 1 mole %, [HEMA] _s was 11 mole %. The intensity of the satellite peak due to the ^* transition of the benzene ring of the styrene component decreased with an increase in [HEMA] _p , to zero at 5 mole % of [HEMA] _p . These results indicate that the HEMA component is localized at the surface.Part CVIII of the series Studies on Suspension and Emulsion.     

(Diisopropylamido) bis (methylcyclopentadienyl) lanthanides as single-component initiators for polymerization of methyl methacrylate

It was first found that (diisopropylamido)bis(methylcyclopentadienyl)lanthanides (MeC₅H₄)₂LnN(i-Pr)₂(THF) (Ln = Yb ( 1 ), Er ( 2 ), Y ( 3 )) exhibit extremely high catalytic activity in the polymerization of methyl methacrylate. The reactions can be carried out over a quite broad range of polymerization temperatures from -78 to 40°C. The catalytic activity of the complexes increases with an increase of ionic radii of the metal elements, i.e. Y > Er > Yb. The results of GPC (gel permeation chromatography) indicate that the number-average molecular weights (M_n) of polymers obtained exceed 100 × 10³ and the molecular weight distribution (M_w/M_n) becomes broad with the increase of temperature. Furthermore highly syndiotactic PMMA (87.7%) can be obtained by lowering the reaction temperature to −78°C. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1593–1597, 1998     

Enantiomeric Purities of (R)- and (S)-Camphors from the Chiral Pool and High Enantiomeric Purities in General

The commercially available camphor enantiomers are extensively used in several important areas of chemical research, and it seems that they are often considered to be enantiomerically pure (the meaning of the term is discussed); there are certainly no enantiomeric purities (e.p.) on record. By standard GLC on a modified cyclodextrin column, we have now found five commercial (R)-camphors to have the same high but imperfect e.p., (99.62 ± 0.02)% (R), a sixth a slightly higher e.p., (99.76 ± 0.06) % (R), and three (S)-camphors to have different and lower e.p. Nailing down these e.p. is useful by itself and puts into focus the sensitivity of present day GLC, and how little is know about high e.p. in general.     

Linear free energy relationships between stability of complex and basicity of ligands: V. The stability of complex formed from 1,10-phenanthroline,N-(p-substituted phenyl) glycines with copper(II), nickel(II), cobalt(II) and zinc(II)

The formation constants (log K ) of ternary mixed ligand complex formed from 1,10-phenanthroline (A, phen) and N-(p-substituted phenyl) glycines,R NHCH₂COOH (B, p RPhG, CH₃, H, CL), with copper (II), nickel (II), cobalt (II) and zinc (II) were determined by pH method at 25°C in 30% (V/V) ethanol solution in presence of 0.1 M NaClO₄. It was found that linear free energy relationships exist between the stability of M(II)-phen-p-RPhG ternary complex and the base strengths of the ligands p-RPhG, conforming to the equation log K = α pK_B +C. The factors influencing the stability of the ternary complex have been discussed. The enhancement of stability of ternary complex was explained in terms of formation of π back bonding between metal ion and the ligand phen. In contrast to the binary system, the ternary ni (II) and zn (II) complexes showed higher stability which could be accounted for by the formation of π back bonding and by intramolecular ligand-ligand interaction, possibly aromatic-ring stacking.     

Stress relaxation and dynamic viscoelastic properties of end-linked poly(dimethyl siloxane) networks containing unattached poly(dimethyl siloxane)

Stress relaxation in uniaxial extension and dynamic shear moduli G′ and G″ have been studied in networks of vinyl-terminated poly(dimethyl siloxane) (PDMS) of five different molecular weights (M _n from 1800 to 29,200) crosslinked with cis-dichlorobis (diethyl sulfide) platinum (II) and containing 10 and 15 wt % of two samples of high-molecular-weight unattached linear hydroxyl-terminated PDMS (M _w 700,000 and 950,000). The M _w/M _n ratio of both the network prepolymers and the unattached linear species was approximately 2. In stress relaxation the stretch ratio was 1.25 or less and the shear relaxation modulus was calculated from the neo-Hookean stress-strain relation. In the dynamic measurements, the strain amplitude was 15% or less; after conversion to the timedependent shear relaxation modulus G(t) the two sets of measurements were combined and the contribution of the unattached species G₁(t) was calculated by difference. After multiplication by (1 − v)⁻¹G/G_e, where v₂ is the volume fraction of network, G is the plateau modulus of the uncrosslinked polymer, and G_e is the equilibrium modulus of the network containing unattached molecules, G₁(t) was compared with G₁₁(t), the relaxation modulus was essentially the same in both environments. The relaxation was slower in the networks than in the uncrosslinked polymer by 1 to 2 orders of magnitude, and it increased gradually with increasing G_e, which is a measure of total to pological obstacles represented by crosslinks plus trapped entanglements. A similar but less striking difference between relaxation in a network and in the homologous environment of a linear polymer was previously observed in end-linked polybutadiene networks and the butadiene phase of a styrene-butadiene-styrene block copolymer. It appears that, in these systems where the topology of the obstacles is fixed, the reptation is severely restricted or else alternative modes of configurational rearrangement which contribute to relaxation in the uncrosslinked polymer are suppressed.     

Photofluorescence of hyperbranched poly(phenylene sulfide)

We synthesized hyperbranched poly(phenylene sulfide) (HPPS) in a simple “one‐pot” way by condensation of potassium 2,4‐dichlorlbenzenthiol. The molecular masses (M_w) of the polymers obtained under the conditions of this work were from 6 × 10³ to 1 × 10⁵. XRD pattern indicated substantial loss in crystallinity in HPPS. There was a minimum in the relation of intrinsic viscosity of HPPS in tetrahydrofuran (THF), determined by Ubbelohde viscometer, to molecular mass. Thermal analysis revealed that the HPPSs were very stable with the onset degradation temperature above 400 °C, and remaining weight of about 60% at 800 °C in nitrogen. The maximum emission wavelength of HPPS in THF was about 460 nm, which would red‐shift with the increase of molecular mass or concentration. The quenching behavior of the fluorescence in HPPS quenched by Cu²⁺ obeyed the Stern–Volmer equation, , where F₀ and F are the fluorescence intensity at the reference condition free of quencher and at condition with a quencher concentration of C_Cu²⁺, respectively, and k is a constant. The quenching efficiency was still as high as about 20% at Cu²⁺ concentration of about 10 ppm. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 826–831, 2006     

Organocatalytic enantioselective synthesis of β-blockers: (S)-propranolol and (S)-naftopidil

An efficient enantioselective synthesis of β-adrenergic blockers (S)-propranolol and (S)-naftopidil with >98% ee using an l-proline-catalyzed α-aminoxylation of an aldehyde as a key step is described.     

Diels-alder reaction of (E)-4-(2-nitroethenyl)-1H-imidazoles and methyl (E)-3-(1-imidazol-4-yl)propenoates

Diels-Alder reaction of methyl (E)-3-(1H-imidazol-4-yl)propenoates 2, 3a-c and (E)4-(2-nitroethenyl)-1H-imidazoles 3d,e with 2,3-dimethyl-1,3-butadiene, cyclopentadiene, and cyclohexa-1,3-diene gave the corresponding cycloadducts 6–9 .