New o-methoxyphenylcyclopentadienylchromium (III) complexes: Synthesis, structures and catalytic properties for ethylene polymerization

Two new ligands 1-(2-methoxyphenyl)-3,4-diphenylcyclopentadiene (1) and 1-(2-methoxyphenyl)-2,3,4,5-tetramethylcyclopentadiene (2), as well as their corresponding cyclopentadienylchromium complexes η⁵-1-(2-methoxyphenyl)-3,4-diphenylcyclopentadienyl chromium dichloride (3) and η⁵-1-(2-methoxyphenyl)-2,3,4,5-tetramethylcyclopentadienyl chromium dichloride (4) were synthesized and characterized. Molecular structures of 3 and 4 were determined by single-crystal X-ray diffraction. Complexes 3 and 4 were tested as catalyst precursors for ethylene polymerization. When activated with Al(ⁱBu)₃ and , complex 3 shows reasonable catalytic activity while 4 exhibits high catalytic activity for ethylene polymerization. The effects of temperature and Al/Cr ratio on the catalytic activity were studied. The molecular weight and melting temperature of the produced polyethylenes were determined.     

Preparation of 1,1-disubstituted silacyclopentadienes

Several new 1,1-disubstituted siloles containing substituents on the ring carbon atoms have been synthesized. The new siloles: 1,1-dihydrido-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (5), 1,1-dihydrido-2,5-dimethyl-3,4-diphenylsilole (6), 1,1-dimethoxy-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (7), 1,1-bis(4-methoxyphenyl)-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (8), 1,1-dipropoxy-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (9), and 1,1-dibromo-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (13) were prepared from reactions originating from the previously reported, 1,1-bis(diethylamino)-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (1) or 1,1-bis(diethylamino)-2,5-dimethyl-3,4-diphenylsilole (2). In addition, three other new organosilane byproducts were observed and isolated during the current study, bis(4-methoxyphenyl)bis(phenylethynyl)silane (11), bis(4-methoxyphenyl)di(propoxy)silane (12) and 1-bromo-4-bromodi(methoxy)silyl-1,4-bis(trimethylsilyl)-3,4-diphenyl-1,3-butadiene (14). Compounds 13 and 14 were characterized by X-ray crystallography and 14 is the first 1,1-dibromosilole whose solid state structure has been determined.     

Preparation of 6-chloropyrazolo[3,4-b]pyridine-5-carbaldehydes by Vilsmeier-Haack reaction and its use in the synthesis of heterocyclic chalcones and dipyrazolopyridines

Novel 6-chloropyrazolo[3,4-b]pyridine-5-carbaldehydes 5 have been synthesized from the 4,5-dihydropyrazolo[3,4-b]pyridine-6-ones 4 via Vilsmeier-Haack reaction. Further treatment of carbaldehydes 5 with acetophenones 6 and hydrazine hydrate afforded chalcone analogues 7 and dipyrazolo[3,4-b:4′,3′-e]pyridines 8, respectively.     

Synthesis and structural chemistry of bis(pyridylimino)isoindolato-ruthenium complexes and their activity as mediators in the atom transfer radical polymerization (ATRP) of styrene

The reaction of the Bispyridyl Isoindole (BPI) type ligands L1 and L2 (L1 = 1,3-Bis(2-(4-tert-butylpyridyl)imino) isoindole, L2 = 1,3-Bis(2-(5-bromo)imino)-5,6-dimethylisoindole) with [Ru(μ-Cl)₂(cod)]_x in presence of triethylamine using coordinating solvents like acetonitrile, dimethyl sulfoxide or pyridine cleanly gave the complexes [{BPI(L1,L2)}Ru^II(Cl)(S)₂] (L1: S = acetonitrile (1), dimethyl sulfoxide (2), pyridine (3); L2: S = acetonitrile (4), dimethyl sulfoxide (5), pyridine (6)). In these complexes the BPI ligands meridionally coordinated to the ruthenium center as established by X-ray diffraction for complexes 3 and 6. The catalytic activity in the direct ATRP (Atom Transfer Radical Polymerization) of styrene was tested for complexes 1-6.     

Thieno[3,4-c]pyrrole-incorporated quinoidal terthiophene with dicyanomethylene termini: synthesis, characterization, and redox properties

Synthesis, characterization, molecular structure, and redox properties of a new quinoidal terthiophene incorporated with a thieno[3,4-c]pyrrole moiety (5) are described. Although an electrochemical reduction of 5 formally produces the non-classical thieno[3,4-c]pyrrole moiety, 5 showed a reversible reduction wave on cyclic voltammogram, indicating that the thieno[3,4-c]pyrrole moiety can be stabilized by delocalized 10π-conjugated system in the dianion state of 5. However, the reduction potential was largely affected by incorporation of the thieno[3,4-c]pyrrole and shifted cathodically by 0.4 V compared to that of the parent quinodial terthiophene (1).     

Macromolecular polyyne-containing benzoxazines for cross-linked polymerization

A Mannich condensation of 2,4-di-tert-butylphenol, p-bromophenethylamine, and formaldehyde followed by a Sonogashira coupling of the resulting 3-(4-bromophenethyl)-6,8-di-tert-butyl-3,4-dihydro-2H-benz[1,3]oxazine (1-Br) with TMSCCH gave acetylenic benzoxazine 1-C₂TMS which was a precursor for polyynic derivatives. Firstly, it was deprotected with K₂CO₃ in iPrOH/MeOH to give the terminal acetylene 1-C₂H, which was subsequently dimerized to the symmetrical diyne 1-C₄-1. Next, 1-C₂H was transformed to 1-C₄TMS via a Cadiot-Chodkiewicz coupling, and then 1-C₄TMS was homocoupled with in situ deprotection to give octatetrayne 1-C₈-1. X-ray diffraction studies of 1-C₈-1 showed distinctive chain bending and a packing analysis revealed the potential for 1,n-topochemical polymerization that implies a cross-linking opportunity.     

Dinuclear titanium complexes with methylphenylsilylene bridge between cyclopentadienyl rings. Synthesis, characterization and reactivity towards ethylene

The new ansa-titanocene dichloride [{(SiMePh)(η⁵-C₅H₄)₂}TiCl₂] (1) was prepared by one pot reaction, whereas synthesis of its methylated analogue [{(SiMePh)(η⁵-C₅Me₄)₂}TiCl₂] (3) was performed in two steps with isolation of corresponding silane intermediate SiMePh(HC₅Me₄)₂ (2). The reaction of 1 and 3 with TiCl₄ afforded the dinuclear complexes [(SiMePh){(η⁵-C₅R₄)TiCl₃}₂] (R = H (4) and R = Me (5)). The catalysts formed from 4 and 5 after their activation with excess MAO exhibited a modest activity in ethylene polymerization. The polymer products consisted of high molar mass linear polyethylenes with a broad molar mass distribution. The presence of three paramagnetic titanium species in the mixture 4/MAO was revealed by EPR spectroscopy. All new prepared compounds 1-5 were characterized by multinuclear NMR, EI-MS, IR, and solid-state structures of 1, 3 and 5 were determined by X-ray single crystal diffraction.     

Imino Diels-Alder reaction of boronates. Preparation and characterization of new 3,4-dihydroquinoline and 1,2,3,6-tetrahydropyridine derivatives

The preparation of 3,4-dihydroquinolines (2a-d and 3a,b,d), as well as 1,2,3,6-tetrahydropyridines (4a-e) by imino Diels-Alder reaction of boronates (1a-e) with 2,3-dimethylbutadiene is reported. Boronates (1a-d) containing substituents meta and para relative to the imino fragment lead to diastereomeric mixtures of 4-methyl-4-ethenyl-3,4-dihydroquinolines (2, 3) and tetrahydropyridines (4). In contrast, the presence of an electron withdrawing substituent at the para position (1e), favors the iminodienophile behavior giving 4,5-dimethyl-1,2,3,6-tetrahydropyridine (4e) as the main product. The results show that boronates derived from Schiff bases are electron deficient species which can act either as dienophiles or dienes in the reaction with 2,3-dimethylbutadiene to give 3,4-dihydroquinolines and 1,2,3,6-tetrahydropyridines. All products were characterized by NMR and X-ray diffraction analysis of 2b, 2d, 3d and 4c allowed to assign the relative configuration of the newly formed stereogenic centers.     

The first asymmetric synthesis of all four isomers of cis- and trans-3,4-dihydroxy-3,4-dihydromollugin

Asymmetric synthesis of all the four stereoisomers of cis-3,4-dihydroxy-3,4-dihydromollugins 4 and 6 and trans-3,4-dihydroxy-3,4-dihydromollugins 5 and 7 was achieved. The O-methoxymethyl mollugin derivatives were dihydroxylated to (−)- and (+)-cis-3,4-dihydroxy-3,4-dihydromollugin derivatives using both AD-mix-α and AD-mix-β. Deprotection of the MOM-ethers of cis-dihydroxy compounds resulted in the targeted stereoisomers (−)-(3R,4R)-cis-3,4-dihydroxy-3,4-dihydromollugin 4, (−)-(3R,4S)-trans-3,4-dihydroxy-3,4-dihydromollugin 5, (+)-(3S,4S)-cis-3,4-dihydroxy-3,4-dihydromollugin 6 and (+)-(3S,4R)-trans-3,4-dihydroxy-3,4-dihydromollugin 7. These routes were paved with difficulties, for example, incompatibility of the substrates with AD-mixes, the unexpected formation of trans-dihydroxy compounds and failures in deprotection protocols.     

3,4-seco-Diterpenoids from Trigonostemon flavidus

Phytochemical investigation on the stems of Trigonostemon flavidus resulted in the isolation of five new 3,4-seco-diterpenoids, trigoflavidones A-E (1-5), structurally related to the main co-occurring known 3,4-seco-sonderianic acid (6) and 3,4-seco-sonderianol (7). Compound 4 possesses new 3,4-seco rearranged ent-pimarane skeletal type, characteristic of a vinyl group at C-8, while 5 features a unique five-membered ring (C₁) fused with a cyclopropane ring (C₂). The structures of the new compounds were established by a combination of spectroscopic data and computational methods. Compounds 1-7 were tested for their cytotoxicities on HL-60, SMMC-7721, A-549, MCF-7, and SW480 human tumor cell lines.     

Substituent-induced regioselective synthesis of 1,2-teraryls and pyrano[3,4-c]pyran-4,5-diones from 2H-pyran-2-ones

Substituent-controlled regioselective synthesis of highly functionalized 1,2-teraryls 3a-k has been achieved through ring transformation of 6-aryl-4-(pyrrolidin-1-yl/piperidin-1-yl)-2H-pyran-2-one-3-carbonitriles 1a-g by aryl acetones 2a-c in the presence of powdered KOH in DMF in very good yield. Under similar reaction conditions, 6-aryl-4-methylsulfanyl-2H-pyran-2-ones 5a-f afforded 1,7-diaryl-2-methyl-4H,5H-pyrano[3,4-c]pyran-4,5-diones 6a-j as major products and 3,4-diaryl-2-methyl-6-methylsulfanylbenzonitriles as minor constituents 7a-j.     

CAN-mediated oxidative cleavage of 4-aryl-3,4-dihydroxypiperidines

A CAN-mediated oxidative cleavage of 4-aryl-3,4-dihydroxypiperidines 2Aa-Be to β-amino carbonyl compounds 3Aa-Be and 4Aa-Be in different ratios is described. This facile strategy was also used to synthesize racemic fluoxetine (5).     

Substituent dependent regioselective synthesis of pyranopyrandiones and 1,2-teraryls from 2H-pyran-2-ones

The one-pot substituent-directed regioselective synthesis of 1,7-diaryl-2-methyl-4H,5H-pyrano[3,4-c]pyran-4,5-diones 3 as the major and 3,4-diaryl-2-methyl-6-methylsulfanylbenzonitriles 4 as the minor products has been delineated through ring transformation of suitably functionalized 2H-pyran-2-ones 1 with aryl acetones 2. Under similar reaction conditions, 6-aryl-4-sec-amino-2H-pyran-2-ones 5 led, regioselectively, to 3,4-diaryl-2-methyl-6-sec-aminobenzonitriles 6.     

Study on the reactions of ethyl 4,4,4-trifluoro-3-oxobutanoate with arylidenemalononitriles

In the presence of a catalytic amount of NEt₃, ethyl 4,4,4-trifluoro-3-oxobutanoate 1 reacted readily with arylidenemalononitriles 2 in ethanol at room temperature. It gave two products 2-trifluoromethyl-3,4-dihydro-2H-pyran derivatives 3 and 2-(trifluoromethyl)piperidine derivatives 4, the ratio of 3 and 4 was depended on the substrates 2 and reaction solvents. Reflux of the ethanol solution of 4 with a catalytic amount of NEt₃ afforded 2-trifluoromethyl-1,4,5,6-tetrahydropyridine derivatives 5 in moderate to good yields. The structures of new compounds 3, 4 and 5 were determined by spectral methods, microanalysis and X-ray diffraction analysis. A possible reaction mechanism for the formation of 3, 4 and 5 was presented.     

Zirconocene complexes with a biphenyl substituted cyclopentadienyl ligand: synthesis, characterization, and olefin polymerization behavior

Novel zirconocene complexes (1-Biph-3,4-Me₂Cp)₂ZrCl₂ (3), (C₅Me₅)(1-Biph-3,4-Me₂Cp)ZrCl₂ (4), and (C₅H₅)(1-Biph-3,4-Me₂Cp)ZrCl₂ (5) containing a 1-biphenyl-3,4-dimethylcyclopentadienyl ligand (2) have been prepared and their solid state structures were characterized by X-ray diffraction method. The crystal structure of 3 revealed a racemic, C₂-symmetric nature in the solid state. In ethylene polymerization, they all afforded high-density polyethylene with very high activity. Especially, the catalytic properties of 3 were most marked in terms of both polymerization activity and molecular weight of polyethylene among them. They also showed good activity on the polymerization of propylene, but afforded nearly atactic, amorphous polypropylenes with a little higher [mmmm] methyl pentad values by 3 and 4 than that by the most active 5 under the given reaction conditions.     

1,2,5-Thiadiazole 2-oxides: selective synthesis,structural characterization,and electrochemical properties

A new general procedure for the selective synthesis of 1,2,5-thiadiazole 2-oxides (including fused derivatives) 8a,b,c,g,h from the reaction of vic-glyoximes with S₂Cl₂ and pyridine in acetonitrile was elaborated together with general procedure for the synthesis of 1,2,5-thiadiazoles 7a–i, 10, 12, and 14 from the same starting materials and reagents. Molecular structures of 3,4-dimethyl-1,2,5-thiadiazole 2-oxide 8a and [1,2,5]thiadiazolo[3,4-b]quinoxaline 10 were confirmed by single-crystal X-ray diffraction. Electrochemical properties of 1,2,5-thiadiazole 2-oxides 8 were studied by cyclic voltammetry and different behavior was observed for monocyclic and benzo-fused derivatives. With compounds 8g and 17, previously unknown deoxygenation of 2,1,3-benzothiadiazole 1-oxides was discovered by electrochemical reduction, and resulted 2,1,3-benzothiadiazoles 7g and 19 were detected in the forms of their radical anions by EPR spectroscopy combined with DFT calculations.     

New emissive fac-tricarbonylchlorobis(ligand)rhenium(I) complexes prepared from pyridine/thiophene hybrid ligands

Stille coupling between tributyl-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-5-yl)-stannane and 4-bromopyridine resulted in the preparation of the new pyridine/thiophene hybrid ligand 4-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-5-yl)-pyridine [4-py-EDOT] (1). Reaction of 1, 4-thiophen-2-yl-pyridine (2), or 4-[2,2^′]bithiophenyl-5-yl-pyridine (3) with ClRe(CO)₅ resulted in the isolation of complexes 4-6, ClRe(L)₂(CO)₃, where L=1, 2, or 3 respectively. The solid-state structure of 4 was determined by X-ray crystallography, which clearly shows the fac arrangement of the three CO ligands and the two 4-py-EDOT ligands arranged cis to one another. The metal complexes 4-6 have been characterized by ¹H and ¹³C NMR, ESI or FAB MS, FTIR, UV-Vis, fluorescence, and elemental analysis.     

Polyhydroxylated pyrrolidines. Part 4: Synthesis from d-fructose of protected 2,5-dideoxy-2,5-imino-d-galactitol derivatives

The readily available 3-O-benzoyl-4-O-benzyl-1,2-O-isopropylidene-5-O-methanesulfonyl-β-d-fructopyranose (5) was straightforwardly transformed into its d-psico epimer (8), after O-debenzoylation followed by oxidation and reduction, which caused the inversion of the configuration at C(3). Compound 8 was treated with lithium azide yielding 5-azido-4-O-benzyl-5-deoxy-1,2-O-isopropylidene-α-l-tagatopyranose (9) that was transformed into the related 3,4-di-O-benzyl derivative 10. Cleavage of the acetonide in 10 to give 11, followed by regioselective 1-O-pivaloylation to 12 and subsequent catalytic hydrogenation gave (2R,3S,4R,5S)-3,4-dibenzyloxy-2,5-bis(hydroxymethyl)-2′-O-pivaloylpyrrolidine (13). Stereochemistry of 13 could be determined after O-deacylation to the symmetric pyrrolidine 14. Total deprotection of 14 gave 2,5-imino-2,5-dideoxy-d-galactitol (15, DGADP).     

Regioselective synthesis of fused benzopyrazolo[3,4-b]quinolines under solvent-free conditions

New 6,8-dihydro-5H-benzo[f]pyrazolo[3,4-b]quinolines 6 have been obtained in a novel solvent-free three-component reaction involving β-tetralone along with 5-aminopyrazoles 1 and benzaldehydes 2. The isomeric 6,10-dihydro-5H-benzo[h]pyrazolo[3,4-b]quinolines 9 could not be prepared in a similar fashion directly from α-tetralone, but were obtained by the reaction of amines 1 with benzylidene-derivative 10 of α-tetralone in similar conditions. The yields of quinolines obtained via this novel protocol were good and the reaction times varied from few minutes to just few seconds.     

New approach to (−)-polyoxamic acid and 3,4-diepipolyoxamic acid from d-lyxono-1,4-lactone

The non-natural enantiomer of polyoxamic acid (1) and 3,4-diepipolyoxamic acid (2) was synthesized in four steps from d-lyxono-1,4-lactone (4). Regioselective bromination of unprotected d-lyxono-1,4-lactone with HBr/AcOH led to 2-bromo-2-deoxy-d-xylono-1,4-lactone (5). This intermediate was treated with NaN₃ to give 2-azido-2-deoxy-d-lyxono and xylono-1,4-lactones. Saponification of the obtained 2-azido derivatives gave the corresponding 2-azido-2-deoxyaldonic acids salt which, after neutralization followed by reduction, led to the expected compounds: (−)-polyoxamic acid (3) and 3,4-diepipolyoxamic acid (2) in 38% and 29% overall yields.