Porphyrin N-Pincer Pd(II)-Complexes in Water: A Base-Free and Nature-Inspired Protocol for the Oxidative Self-Coupling of Potassium Aryltrifluoroborates in Open-Air

Metalloporphyrins (and porphyrins) are well known as pigments of life in nature, since representatives of this group include chlorophylls (Mg-porphyrins) and heme (Fe-porphyrins). Hence, the construction of chemistry based on these substances can be based on the imitation of biological systems. Inspired by nature, in this article we present the preparation of five different porphyrin, meso-tetraphenylporphyrin (TPP), meso-tetra(p-anisyl)porphyrin (TpAP), tetrasodium meso-tetra(p-sulfonatophenyl)porphyrin (TSTpSPP), meso-tetra(m-hydroxyphenyl)porphyrin (TmHPP), and meso-tetra(m-carboxyphenyl)porphyrin (TmCPP) as well as their N-pincer Pd(II)-complexes such as Pd(II)-meso-tetraphenylporphyrin (PdTPP), Pd(II)-meso-tetra(p-anisyl)porphyrin (PdTpAP), Pd(II)-tetrasodium meso-tetra(p-sulfonatophenyl)porphyrin (PdTSTpSPP), Pd(II)-meso-tetra(m-hydroxyphenyl)porphyrin (PdTmHPP), and Pd(II)-meso-tetra(m-carboxyphenyl)porphyrin (PdTmCPP). These porphyrin N-pincer Pd(II)-complexes were studied and found to be effective in the base-free self-coupling reactions of potassium aryltrifluoroborates (PATFBs) in water at ambient conditions. The catalysts and the products (symmetrical biaryls) were characterized using their spectral data. The high yields of the biaryls, the bio-mimicking conditions, good substrate feasibility, evading the use of base, easy preparation and handling of catalysts, and the application of aqueous media, all make this protocol very attractive from a sustainability and cost-effective standpoint.     

Microwave-assisted synthesis of N,N-bis-(2-pyridylmethyl)amine derivatives. Useful ligands in coordination chemistry

Microwave-assisted synthesis of the ligands N,N-bis-(2-pyridylmethyl)amine (BMPA), N-(methylpropanoate)-N,N-bis-(2-pyridylmethyl)amine (MPBMPA), N-(propanamide)-N,N-bis-(2-pyridylmethyl)amine (PABMPA), PNBMPA (N-(3-propionitrile)-N,N-bis-(2-pyridylmethyl)amine), N-(3-aminopropyl)-N,N-bis-(2-pyridylmethyl)amine (APBMPA), and lithium N-(proponoate)-N,N-bis-(2-pyridylmethyl)amine (LiPBMPA) are reported. High yields and short reaction time were obtained for condensation and Michael addition.     

Antibacterial activity of N-quaternary chitosan derivatives: Synthesis, characterization and structure activity relationship (SAR) investigations

Quaternary N-(2-(N,N,N-tri-alkyl ammoniumyl and 2-pyridiniumyl) acetyl) derivatives of chitosan polymer, chitooligomer, and glucosamine (monomer) were synthesized for the purpose of investigating the structure activity relationship (SAR) for the antibacterial effect. Novel methods were used in the synthesis. The final chitosan and chitooligomer derivatives could thus be obtained in two steps without prior protection of the hydroxyl groups. However, in order to obtain chitosan derivatives with the bulky N,N-dimethyl-N-dodecyl- and N,N-dimethyl-N-butyl side chains three steps were needed, starting from 3,6-O-di-tert-butyldimethylsilyl chitosan (3,6-O-di-TBDMS chitosan) as the key intermediate. The quaternary ammoniumyl acetyl derivatives of glucosamine were synthesized from glucosamine or tetra-O-acetylglucosamine. N,N,N-trimethyl chitosan (TMC) was used as reference compound for investigation of antibacterial activity. Clinical Laboratory Standard Institute (CLSI) protocols were used to determine MIC and MLC for activity against clinically important Gram-positive strains Staphylococcus aureus (ATCC 25923), and S. aureus (MRSA) (ATCC 43300), and Gram-negative strains of Escherichia coli (ATCC 25922), P. aeriginosa (ATCC 27853) and Enterococcus facialis (ATCC 29212). The MIC values for the compounds ranged from 8 to ?8192 mg/L. In general the N-(2-(N,N-dimethyl-N-dodecyl ammoniumyl) acetyl) derivatives of chitooligomer and glucosamine monomer were more active against bacteria than derivatives with shorter alkyl chains. In contrast the N-(2-(N,N-dimethyl-N-dodecyl ammoniumyl) acetyl) derivatives of chitosan were less active than derivatives with N-(2-N,N,N-trimetylammoniumyl) acetyl or N-(2-(N-pyridiniumyl) acetyl) quaternary moiety. N,N,N-trimethyl chitosan (TMC) was the most active compound in this study.     

An efficient and stereodivergent synthesis of threo- and erythro-β-methylphenylalanine. Resolution of each racemic pair by semipreparative HPLC

threo and erythro diastereoisomers of the constrained amino acid (βMe)Phe can be obtained separately on a multigram scale through a three-step synthesis from the corresponding Z and E isomers of 2-phenyl-4(α-phenylethylidene)-5(4H)-oxazolone. The 5(4H)-oxazolones are readily available from acetophenone and hippuric acid. The four enantiomerically pure isomers of β-methylphenylalanine, (2R,3R)-(βMe)Phe, (2S,3S)-(βMe)Phe, (2R,3S)-(βMe)Phe and (2S,3R)-(βMe)Phe, have been prepared by HPLC resolution of the racemic precursors methyl threo (or erythro)-2-benzamide-3-phenylbutanoates.     

Molecular structure and conformation of gaseous bromoacetyl chloride and bromoacetyl bromide as determined by electron diffraction

Bromoacetyl chloride and bromoacetyl bromide are studied by gas phase electron diffraction at nozzle-tip temperatures of 70°C and 77°C, respectively. Both compounds exist as mixtures of anti and gauche conformers. The mole fraction anti, with uncertainties estimated at 2σ, was found to be 0.474(0.080) for bromoacetyl chloride and 0.615(0.069) for bromoacetyl bromide. The results for the distance (r_a)and angle (∠α) parameters, with parenthesized uncertainties of 2σ including estimated uncertainty in the electron wave length and correlation effects are as follows: (1) bromoacetyl chloride, r(C-H) = 1.086(0.062) Å, r(CO) = 1.188(0.009) Å, r(C-C) = 1.519(0.018) Å, r(C-Cl) = 1.789(0.011) Å, r(C-Br) = 1.935(0.012) Å, ∠C-CO = 127.6(1.3)°, ∠C-C-Cl = 111.3(1.1)°, ∠C-C-Br = 111.0(1.5)°, ∠H-C-H = 109.5°(assumed), $\text{}\text{?}$/o (gauche torsion angle relative to 0° for the anti form) = 110.0°(assumed); (2) bromoacetyl bromide, r(C-H) =1.110(0.088) Å, r(C=O) = 1.175(0.013) Å, r(C-C) = 1.513(0.020) Å, r(CO-Br) = 1.987(0.020) Å, r(CH₂-Br) = 1.915(0.020) Å, ∠C-CO = 129.4(1.7)°, ∠CH₂-CO-Br = 110.7(1.5)°, ∠CO-CH₂-Br = 111.7(1.8)°, ∠H-C-H = 109.5°(assumed), ∠ø (gauche torsion angle relative to 0° for the anti form) = 105.0°(assumed). The structural results are discussed in connection with the structures of related molecules.     

Fluorsilylsubstituierte N,N- und N,O-bis(trimethylsilyl)-hydroxylamine

Fluoro- und aminofluoro-silanes react with the lithium salt of N,O-bis(trimethylsilyl)hydroxylamine under LiF elimination and substitution. Alkyl- and amino-fluorosilanes give O-fluorosilyl-N,N-bis(trimethylsilyl)hydroxylamines, arylfluorosilanes give N-fluorosilyl-N,O-bis(trimethylsilyl)hydroxylamines. By the further reaction of O-difluorosilyl-N,N-bis(trimethylsilyl)hydroxylamine with the lithiated hydroxylamine, O,O′-fluoromethylsilyldi[N,N-bis(trimethylsilyl)hydroxylamine] is formed. On heating N-difluorophenylsilyl-N,O-bis(trimethylsilyl)hydroxylamine di[fluorophenylsilyl(methyl)amino]pentamethylsiloxane is formed by methyl group migration. The NMR and mass spectra of the compounds are reported.     

Synthesis of new thietanylpyrimidine and thietanylimidazole derivatives

New thietanyl-substituted derivatives of pyrimidine-2,4(1H,3H)-dione and imidazole were synthesized. The alkylation of 6-methylpyrimidine-2,4(1H,3H)-diones with 2-chloromethylthiirane in water involved the N¹ atom of the pyrimidine ring and afforded 6-methyl-1-(thietan-3-yl)-pyrimidine-2,4(1H,3H)-diones. Under analogous conditions 6-aminopyrimidine-2,4(1H,3H)-dione gave rise to 6-(thietan-3-ylamino)pyrimidine-2,4(1H,3H)-dione. Unsymmetrically substituted 2-methyl-4(5)-nitro- and 5(4)-bromo-2-methyl-4(5)-nitro-1H-imidazoles reacted with 2-chloromethylthiirane to produce mixtures of isomeric 2-methyl-4(5)-nitro-1-(thietan-3-yl)-1H-imidazoles and 5(4)-bromo-2-methyl-4(5)-nitro-1-(thietan-3-yl)-1H-imidazoles.     

Preparation and Crystal Structures of 4-(4′-Pyridylthio)-1-methylpyridinium Salts: Assembly of a Donor-Acceptor-Type Molecule Containing a Sulfide Bridge

A series of ionic 4-(4′-pyridylthio)-1-methylpyridinium salts with different counteranions (1, I⁻; 2, BF⁻₄; 3, PF⁻₆; and 4, OTf⁻, where OTf=trifluoromethanesulfonate) have been prepared. Structural analysis reveals that the cation exhibits a variety of stacking structures dependent on the anion. Compound 1 crystallizes in space group P2_1/n (#14), with a=10.764(3) Å, b=9.601(5) Å, c=13.105(3) Å, β=108.35(2), V=1285.4(8) ų, and Z=4. In this compound, each cation moiety is stacked in a helical arrangement along the c-axis. Compound 2, which is isomorphous to 1, has space group P2_1/n (#14), with a=11.647(2) Å, b=9.203(3) Å, c=13.232(2) Å, β=108.42(2), V=1345.6(5) ų, and Z=4. Compound 3 crystallizes in space group P2_1/n (#14), with a=8.06(1) Å, b=17.43(1) Å, c=10.30(1) Å, β=103.0(1), V=1410(3) ų, and Z=4. In this salt, the cation molecules assume a head-to-tail stacking arrangement, forming a polar pseudo 1-D chain. Compound 4 crystallizes in space group Pb? (#2), with a=7.585(4) Å, b=15.443(7) Å, c=6.775(4) Å, α=99.33(4), β=108.35(2)^o, γ=98.37(4), V=756.6(7) ų, and Z=2. The structure of 4 consists of a columnar stacking of pyridine moieties, with the cation moieties surrounded by the counteranions. Calculations show that the 4-(4′-pyridylthio)-1-methylpyridinium cation may be a good building block for second harmonic generation (SHG) materials, even though salts 1-4 crystallized in centrosymmetric structures and were SHG inactive.     

ABA triblock copolymers with pendant hydroxyl groups prepared by controlled cationic polymerization and their use as delivery carrier for paclitaxel

To improve the hydrophilicity of poly(styrene-b-isobutylene-b-styrene) (SIBS), this study focuses on the synthesis of novel functional ABA triblock copolymer thermoplastic elastomers (TPEs) with polyisobutylene (PIB) as rubbery segments. The precursor poly{(styrene-co-4-[2-(tert-butyldimethylsiloxy) ethyl]styrene)-b-isobutylene-b-(styrene-co-4-[2-(tert-butyldimethylsiloxy)ethyl]styrene)}(P(St-co-TBDMES)-PIB-P(St-co-TBDMES)) triblock copolymer was first synthesized by living sequential cationic copolymerization of isobutylene (IB) with styrene (St) and 4-[2-(tert-butyldimethylsiloxy) ethyl]styrene (TBDMES) using 1,4-di(2-chloro-2-propyl)benzene (DiCumCl)/titanium tetrachloride (TiCl₄)/2,6-di-tert-butylpyridine (DtBP) as the initiating system. Then, P(St-co-TBDMES)-PIB-P(St-co-TBDMES) was hydrolyzed in the presence of tetra-butylammonium fluoride to yield poly{[styrene-co-4-(2-hydroxyethyl)styrene]-bisobutylene-b-[styrene-co-4-(2-hydroxyethyl)styrene]} (P(St-co-HOES)-PIB-P(St-co-HOES)) with pendant hydroxyl groups. P(St-co-HOES)-PIB-P(St-co-HOES) used as the paclitaxel carrier was also investigated in this study. Comparing with SIBS, P(St-co-HOES)-PIB-P(St-co-HOES) has exhibited better compatibility with paclitaxel and higher release rate.     

New chiral phosphine-phosphonites derived from (2R,3R)-dimethyl tartrate, (S)-binaphthol and (1R,2S)-ephedrine

The reaction of 2-lithiophenyldiphenylphosphine with phosphorus trichloride afforded the new unsymmetric phosphine, dichloro(2-diphenylphosphinophenyl)phosphine (4). Condensation of 4 with (a) (2R,3R)-dimethyl tartrate or (b) (S)-binaphthol in the presence of triethylamine gave new chiral phosphine-phosphonite ligands, (2R,3R)-[2-(2′-(diphenylphosphino)phenyl)-4,5-bis(carbomethoxy)-1,3,2-dioxaphospholane] ((2R,3R)-5) and (S)-[2-(diphenylphosphino)benzene][1,1′-binaphthalen-2,2′-diyl]phosphonite] ((S)-6). The analogous reaction of 4 with (1R,2S)-ephedrine using N-methylmorpholine as the base, gave [2-(2′-(diphenylphosphino)phenyl)-3,4-dimethyl-5-phenyl-1,3,2-oxazaphospholidine] (7) as a 95:5 mixture of diastereoisomers.     

Synthesis,Characterization, and Antiproliferative Activity of Novel Chiral [QuinoxP*AuCl2]+ Complexes

Herein is reported the synthesis of two Au(III) complexes bearing the (R,R)-(–)-2,3-Bis(tert-butylmethylphosphino)quinoxaline (R,R-QuinoxP*) or (S,S)-(+)-2,3-Bis(tert-butylmethylphosphino)quinoxaline (S,S-QuinoxP*) ligands. By reacting two stoichiometric equivalents of HAuCl₄.3H₂O to one equivalent of the corresponding QuinoxP* ligand, (R,R)-(–)-2,3-Bis(tert-butylmethylphosphino)quinoxalinedichlorogold(III) tetrachloroaurates(III) (1) and (S,S)-(+)-2,3-Bis(tert-butylmethylphosphino)quinoxalinedichlorogold(III) tetrachloroaurates(III) (2) were formed, respectively, in moderate yields. The structure of (S,S)-(+)-2,3-Bis(tert-butylmethylphosphino)quinoxalinedichlorogold(III) tetrachloroaurates(III) (2) was further confirmed by X-ray crystallography. The antiproliferative activities of the two compounds were evaluated in a panel of cell lines and exhibited promising results comparable to auranofin and cisplatin with IC₅₀ values between 1.08 and 4.83 µM. It is noteworthy that in comparison to other platinum and ruthenium enantiomeric complexes, the two enantiomers (1 and 2) do not exhibit different cytotoxic effects. The compounds exhibited stability in biologically relevant media over 48 h as well as inert reactivity to excess glutathione at 37 °C. These results demonstrate that the Au(III) atom, stabilized by the QuinoxP* ligand, can provide exciting compounds for novel anticancer drugs. These complexes provide a new scaffold to further develop a robust and diverse library of chiral phosphorus Au(III) complexes.     

Structural, spectral and thermal studies of substituted N-(2-pyridyl)-N′-phenylthioureas

N-2-(3-picolyl)-N′-phenylthiourea, 3PicTuPh, monoclinic, P2₁/n, a=7.617(2) b=7.197(5), c=22.889(5) Å, β=94.63(4)°, V=1250.7(1) Å³ and Z=4; N-2-(4-picolyl)-N′-phenylthiourea, 4PicTuPh, triclinic, P-1, a=7.3960(5), b=7.9660(12), c=21.600(3) Å, α=86.401(4), β=84.899(8), γ=77.769(8)°, V=1237.5(3) Å³ and Z=4; N-2-(5-picolyl)-N′-phenylthiourea, 5PicTuPh, monoclinic, P2₁/c, a=14.201(1), b=4.905(3), c=17.689(3) Å, β=91.38(1)°, V=1231.8(7) Å³ and Z=4; N-2-(6-picolyl)-N′-phenylthiourea, 6PicTuPh, monoclinic, C2/c2, a=14.713(1), b=9.367(1), c=18.227(1) Å, β=92.88(1)°, V=2515.5(1) Å³ and Z=8 and N-2-(4,6-lutidyl)-N′-phenylthiourea, 4,6LutTuPh, monoclinic, C2/c, a=11.107(2), b=11.793(2), c=20.084(4) Å, β=96.10(3)°, V=2616(1) Å³ and Z=8. Intramolecular hydrogen bonding between N′H and the pyridyl nitrogen and intermolecular hydrogen bonding involving the thione sulfur are affected by substitution of the pyridine ring, as is the planarity of the molecule. ¹H NMR studies in CDCl₃ show the NH′ hydrogen resonance considerably downfield from other resonances in the spectrum for each thiourea.     

Fluorocyclohexanes. Part XVII. Dehydrofluorinations of the cis and the trans isomers of 2H-1-(difluoromethyl)decafluorocyclohexane

2H-1-(Difluoromethyl)octafluorocyclohex-1-ene (I) and cobalt trifluoride at 165 °C afforded 2H-1-(trifluoromethyl)octafluorocyclohex-1-ene (IV) and four decafluorocyclohexane derivatives: the cis (III), and trans (V), -2H-1-(trifluoromethyl)-; the cis (VII), and trans (VI), 2H-1-(difluoromethyl) compounds. Dehydrofluorination of VII, using aqueous potassium hydroxide, gave only one alkene, 1-(difluoromethyl)nonafluorocyclohex-1-ene (VIII). In a slower reaction VI afforded two alkenes, mainly VIII, But also an isomer, 1-(difluoromethyl)nonafluorocyclohex-2-ene (IX) (ratio 2:1).     

A practical synthesis of new S,N-disubstituted derivatives of 5-(4-methylpiperidino)methyl-2-thiouracil

5-(4-Methylpiperidino)methyl-2-thiouracil (1) has been obtained via the Mannich reaction between 2-thiouracil, paraformaldehyde, and a cyclic secondary amine such as 4-methylpiperidine (4-MP) in ethanol. New S,N(1)-di-o-(m- and p-)bromo-(nitro-) benzyl-substituted derivatives have been synthesized successfully in the reactions of 1 with the corresponding o-(m- and p-)bromobenzyl bromides or o-(m- and p-) nitrobenzyl chlorides in DMF solution in the presence of K₂CO₃. The opposite method of synthesis, that is, the reaction between 2-o-(m- and p-)bromobenzylthio-1-o-(m- and p-)bromobenzyluracils and 2-o-(m- and p-)nitrobenzylthio-1-o-(m- and p-) nitrobenzyluracils (8), with paraformaldehyde and 4-methylpiperidine in ethanol failed, indicating the important role of the enol form of 2-thiouracil for the Mannich reaction to be successful.     

Thermal decomposition of trans-chloro(2-allylphenyl)bis(triethylphospine)nickel(II)

Thermolysis of trans-chloro(2-allylphenyl)bis(triethylphosphine)nickel(II), I, in tetrachloroethylene has afforded indene as the major hydrocarbon product along with lesser amounts of allylbenzene and trans-β-methylstyrene. Organonickel products were trans-chloro(trichlorovinyl)bis(triethylphosphine)nickel(II), II, chloro[2-(trans-propenyl)phenyl]bis(triethylphosphine)nickel(II), III, and trans-dichlorobis(triethylphosphine)nickel(II). Compound III was the major product from thermolysis of I in benzene. Chloro[2-(cis-propenyl)phenyl]bis(triethylphosphine)nickel(II), IV, and III could be synthesized independently by treatment of chloro-2-(cis-propenyl)benzene and chloro-2-(trans-propenyl)benzene, respectively, with nickel acetylacetonate and triethylaluminium in the presence of triethylphosphine. Thermolysis of I in benzene containing allylbenzene led to the formation of trans-β-methylstyrene. The thermolysis of I in benzene in the presence of cis-1,4-hexadiene caused the skeletal rearrangement of the diene to trans-2-methyl-1,3-pentadiene. A catalyst derived from ethylenebis(triphenylphosphine)nickel(0) and hydrogen chloride isomerized allylbenzene to trans-β-methylstyrene.     

Synthesis, crystal structure, and magnetic properties of a cobalt(II) complex with (3,5-dichloropyridin-4-yl)(pyridin-4-yl)methanol

A novel bridging ligand, (3,5-dichloropyridin-4-yl)(pyridin-4-yl)methanol (I), and its cobalt(II) complex, [Co(I)₂(NCS)₂]_n (II), were prepared. The structures of ligand I and complex II were determined by single crystal X-ray analysis. Magnetic susceptibility measurements were performed for cobalt (II) complex II. Compound I crystallised in orthorhombic space group Pbca with a = 7.6585(14) Å, b = 12.209(2) Å, c = 23.207(4) Å, V= 2170.0(7) ų and Z=8. Complex II crystallised in monoclinic space group P2₁/n with a = 13.223(8) Å, b = 16.959(10) Å, c = 13.948(8) Å, β = 115.395(10)°, V= 2826(3) ų and Z = 4. Each cobalt(II) ion is surrounded by two NCS^? anions and four pyridyl moieties from two bridging ligands. Each bridging ligand connects two neighbouring Co(II) ions to form a 2-dimensional structure. Temperature dependence of the molar magnetic susceptibilities in the temperature range of 2–300 K revealed that magnetic interactions between the cobalt ions are weak.     

Measurement and Identification of (R)- and (S)-6-O-Desmethylnaproxen Enantiomers as Diastereomeric O-Ethoxycarbonyl/(R)-(+)-1-Phenylethylamides in Urine by GC and GC-MS

Enantioseparations of (R)- and (S)-6-O-desmethylnaproxens as O-ethoxycarbonyl/(R)-(+)-1-phenylethylamides and (R)- and (S)-naproxens as (R)-(+)-1-phenylethylamides were achieved by achiral gas chromatography in a single run within 11 min. The characteristic mass spectral patterns facilitated easier peak identification. The method for determinations of (R)-naproxen (1.0 to 50 ng) and (S)-naproxen (100 to 2000 ng) was linear with acceptable repeatability and accuracy. The enantiomeric composition ratios between (R)- and (S)-6-O-desmethylnaproxens and between (R)- and (S)-naproxens in urine sample collected six hours after oral administration of (S)-naproxen tablets were measured to be 2.2 (± 0.2):97.8 (± 0.2) and 2.1 (± 0.1):97.9 (± 0.1), respectively.     

Michael addition of phenylacetonitrile to the acrylonitrile group leading to diphenylpentanedinitrile. Structural data and theoretical calculations

Knoevenagel condensation of phenylacetonitrile with 4-diphenylaminophenylacetonitrile in the presence of piperidine was carried out to obtain a novel conjugated compound. In addition to the expected compound 2-(phenyl)-3-(4-diphenylaminophenyl)acrylonitrile (I), the 3-((4-diphenylamino)phenyl)-2,4-diphenylpentanedinitrile (II) was also obtained with a good yield. Compound II was obtained as a result of the Michael addition of phenylacetonitrile with 2-(phenyl)-3-(4-diphenylaminophenyl)acrylonitrile (I). Conversely, when the same reaction was performed in the presence of KOH as catalyst, only the α,β-unsaturated nitrile (I) was afforded with a 92 % yield. The structures were confirmed with IR, EI-MS and NMR spectroscopy. Single crystals I and II were formed and their structures were determined by X-ray single-crystal diffraction analysis. Crystal I belongs to the monoclinic system with space group P2₁/n having unit cell parameters of a = 16.8589(5) Å, b = 6.68223(17) Å, c = 19.8289(7) Å, β = 111.133(4)○ and Z = 4. Crystal II belongs to the same monoclinic system with space group P2₁/c, having unit cell parameters of a = 10.8597(4) Å, b = 24.7533(10) Å, c = 9.7832(4) Å, β = 91.297(3)○ and Z = 4. In addition to the structural data analysis, some theoretical calculations that reveal the nature of relevant structure-property relationships are also reported.     

Novel (E)- and (Z)-3(5)-(2-hydroxyphenyl)-4-styrylpyrazoles from (E)- and (Z)-3-styrylchromones: the unexpected case of (E)-3(5)-(2-hydroxyphenyl)-4-(4-nitrostyryl)pyrazoles

An efficient synthetic method for the preparation of (E)- and (Z)-3(5)-(2-hydroxyphenyl)-4-styrylpyrazoles has been developed. The reaction of (E)- and (Z)-3-styrylchromones with hydrazine hydrate afforded the corresponding (E)- and (Z)-4-styrylpyrazoles, respectively, saved 4′-nitro-derivatives where both (E)- and (Z)-4′-nitro-3-styrylchromones afforded (E)-3(5)-(2-hydroxyphenyl)-4-(4-nitrostyryl)pyrazoles. The reaction mechanism for these transformations was discussed and the stereochemistry of all products was assigned by NMR experiments.     

A mild and efficient cyanosilylation of ketones catalyzed by a Lewis acid-Lewis base bifunctional catalyst

A new family of bifunctional catalysts (N-oxides-Ti(OⁱPr)₄ (2:1)) containing a Lewis acid and a Lewis base was developed and applied to the catalytic cyanosilylation of ketones. Utilizing rac((1R,2S) and (1S,2R))-1-(2′-pyridylmethyl)-2-diphenylhydroxymethylpyrrolidine N-oxide-titanium (2:1) complex and N-benzyl-diethanolamine N-oxide-titanium (2:1) complex as catalysts, the cyanosilylation products were obtained in 42-97% yield. Based on experimental phenomena and kinetic studies, a catalytic cycle was proposed to explain the remarkable activities of these catalysts. Investigations indicated that rac((1R,2S) and (1S,2R))-1-(2′-pyridylmethyl)-2-diphenylhydroxymethylpyrrolidine N-oxide-titanium (2:1) complex and N-benzyl-diethanolamine N-oxide-titanium (2:1) complex should promote the reaction via a dual activation of the ketone by the titanium and TMSCN by the N-oxide.