Benzylic triflates prepared in‐situ: novel initiators for mono‐, bi‐ and trifunctional living poly(THF)s

Mono‐, bis‐, and tris(trifluoromethanesulfonate ester)s ((triflate ester)s) were prepared by the reaction of benzyl alcohol ( 1 ), 1,4‐bis(hydroxymethyl)benzene ( 2 ) and 1,3,5‐tris(hydroxymethyl)benzene ( 3 ) with trifluoromethanesulfonic anhydride in the presence of 2,6‐di‐tert‐butylpyridine. These benzylic triflate esters were applied in‐situ for the living polymerization of tetrahydrofuran (THF). The subsequent end‐capping reaction with a suitable nucleophile proceeded quantitatively to produce mono, bi‐ and, in particular, novel trifunctional telechelic poly(THF)s, respectively.     

CZE study on adsorption processes of aliphatic and aromatic amines on PMMA chip

Adsorption processes on a PMMA chip linked with CZE separations of a group of 13 aliphatic and aromatic mono‐ and di‐amines were studied. Due to the lack of chromophores within aliphatic amines, contact conductivity detection implemented directly onto the chip was used for monitoring of cationic CZE separations. To prevent an adsorption of studied amines to the chip channels, the surface of PMMA chip was modified by dynamic coating. Different surface modifiers, such as aliphatic oligoamines (diethylenetriamine and triethylenetetramine), were added to the BGE solutions filling the chip channels. The effect of various concentrations of surface modifiers on peak profiles and separation parameters of amines was monitored. Of these, mainly, aliphatic di‐amines and aromatic mono‐amines adversely affected the CZE resolution of a whole group of analytes by their strong adsorption to the chip channels. A propionate BGE with pH 3.2 containing 100 μM triethylenetetramine and 25 mM 18‐crown‐6‐ether was found suitable for CZE resolution of 12 from a total of 13 amines studied. Simple dynamic modification of the surface of PMMA chip enabled fast (analysis time lasted 9 min), sensitive (sub‐μM LODs reached) and reproducible (1–3% RSD of the peak areas) CZE analysis of the aliphatic and aromatic amines.     

Palladium‐Catalyzed Ligand‐Free C‐N Coupling Reactions: Selective Diheteroarylation of Amines with 2‐Halobenzimidazoles

2‐Aminobenzimidazoles are widely present in a number of bioactive molecules. Generally, the preparation of these molecules could be realized by the mono‐substitution of 2‐halobenzimidazoles with amines. However, rare examples were reported for the di‐substituted products and the selectivity of mono‐ vs. di‐substitution was relatively low. Considering the potential values of the di‐substituted products, we accomplished the first selective diheteroarylation of amines with 2‐halobenzimidazoles. Notably, this Pd‐catalyzed transformation was realized under ligand‐free conditions. Accordingly, numerous target products were efficiently produced from various aromatic or aliphatic amines and 2‐halobenzimidazoles. It was worth noting that two representative products were further confirmed by X‐ray crystallography. More significantly, this catalytic process could be applied to the synthesis and discovery of new bioactive compounds, which demonstrated the synthetic usefulness of this newly developed approach.     

One‐Pot Synthesis of Some Dynamic 2‐Substituted Benzoxazinones and Their Corresponding Qinazolinones of Anticipated Biological Activity

Reactions of 6‐bromo‐2‐isopropyl‐4(3H)‐3,1‐benzoxazin‐4‐one toward mono‐ and di‐dentate nitrogen nucleophiles, e.g. primary aliphatic and aromatic amines, 1,2‐phenylenediamine, hydrazine hydrate, and formamide, have been investigated and afford the corresponding quinazolinones which are expected to have some interesting biological activity. The behavior of 3, 1‐benzoxazin‐4‐one toward active methylene compounds, namely, acetylacetone in basic medium has been studied and gave 3‐acetylquinoline. The last reaction is considered as an illustrative model of heterocyclic transformation reactions.     

Synthesis of Stereoisomers of Cryptofolione 6'-Mono- and 4', 6'-Di-O-benzyl Ethers

Synthesis of stereoisomers of 6′‐mono‐ and 4′,6′‐di‐O‐benzyl cryptofolione is described through a key intermediate 6 , which was prepared by coupling of iodobenzene 8 with chiral propargyl alcohol 9 under Cosford protocol conditions. Monobenzyl ether 4 is obtained via epoxide 6 opening with vinyl Grignard, followed by cross‐metathesis reaction with a vinyl lactone 11 . Whereas, dibenzyl ether 5 is prepared by epoxide 6 opening with chiral propargyl alcohol 7 followed by simple transformations and finally cis‐Wittig olefination.     

Chemical alteration of poly(tetrafluoroethylene) Teflon induced by exposure to vacuum ultraviolet radiation and comparison with exposure to hyperthermal atomic oxygen

The chemical alteration of poly(tetrafluoroethylene) Teflon by vacuum ultraviolet radiation (VUV) (115–400 nm) has been examined with X‐ray photoelectron spectroscopy (XPS). The initial F/C atom ratio of 1.98 decreases to 1.65 after a 2‐h exposure. The F/C atom ratio is further reduced to a steady‐state value of 1.60 after a 74‐h exposure. The high‐resolution XPS C1s data indicate that new chemical states of carbon form as F is removed and that the relative amounts of these states depend on the F content of the near‐surface region. The states are most likely due to C bonded only to one F atom, C bonded only to other C atoms, and C that has lost a pair of electrons through the emission of F^?. The exposure of the VUV‐damaged surface to research‐grade O₂ results in the chemisorption of a very small amount of O, and this indicates that large quantities of reactive sites are not formed during the chemical erosion by VUV. Further exposure to VUV removes this chemisorbed oxygen. A comparison of the XPS data indicates that the mechanisms of chemical alteration by VUV radiation and hyperthermal (～5 eV) atomic oxygen are different, as expected, because the excitation sources are quite different. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 552–561, 2005     

The More Gold—The More Enantioselective: Cyclohydroaminations of γ‐Allenyl Sulfonamides with Mono‐, Bis‐, and Trisphospholane Gold(I) Catalysts

A series of chiral mono‐, di‐, and trinuclear gold(I) complexes have been prepared and used as precatalysts in the asymmetric cyclohydroamination of N‐protected γ‐allenyl sulfonamides. The stereodirecting ligands were mono‐, di‐, and tridentate 2,5‐diphenylphospholanes, which possessed C₁, C₂, and C₃ symmetry, respectively, thereby rendering the catalytic sites in the di‐ and trinuclear complexes symmetry equivalent. The C₃‐symmetric trinuclear complex displayed the highest activity and enantioselectivity (up to 95 % ee), whilst its mono‐ and dinuclear counterparts exhibited considerably lower enantioselectivities and activities. A similar trend was observed in a series of mono‐, di‐, and trinuclear 2,5‐dimethylphospholane gold(I) complexes. Aurophilic interactions were established from the solid‐state structures of the trinuclear gold(I) complexes, thereby raising the question as to whether these secondary forces were responsible for the different catalytic behavior observed.     

Nickel Nanoparticle Catalyzed Mono‐ and Di‐Reductions of gem‐Dibromocyclopropanes Under Mild,Aqueous Micellar Conditions

Mild mono‐ and di‐hydrodehalogenative reductions of gem‐dibromocyclopropanes are described, providing an easy and green approach towards the synthesis of cyclopropanes. The methodology utilizes 0.5–5 mol % TMPhen‐nickel as the catalyst, which, when activated with a hydride source such as sodium borohydride, cleanly and selectively dehalogenates dibromocyclopropanes. Double reduction proceeds in a single operation at temperatures between 20–45 °C and at atmospheric pressure in an aqueous designer surfactant medium. At lower loading and either in the absence of ligand or in the presence of 2,2′‐bipyridine, this new technology can also be used to gain access to not only monobrominated cyclopropanes, interesting building blocks for further use in synthesis, but also mono‐ or di‐deuterated analogues. Taken together, this base‐metal‐catalyzed process provides access to cyclopropyl‐containing products and is achieved under environmentally responsible conditions.     

Controllable Activation of Pd‐G3 Palladacycle Precatalyst in the Presence of Thiosugars: Rapid Access to 1‐Aminobiphenyl Thioglycoside Atropoisomers at Room Temperature

A controllable method for the functionalization of XantPhos Pd‐G3 precatalyst with thiosugars and thiols has been established. Under mild and operationally simple reaction conditions through just mixing of precatalyst and thiosugars (α‐ or β‐mono‐, di‐ and poly‐thiosugar derivatives) in water at 25 °C for 20 min, a series of 1‐aminobiphenyl thioglycosides that are difficult to synthesize by classical methods has been synthesized in very high yields.     

Separation of acetins by counter-current chromatography

In this work we report the purification of a crude acetin mixture into mono‐, di‐ and triacetin by countercurrent chromatography. The process was initially tested on a small, semi‐preparative scale (0.5 g) to determine its efficiency. The process was then scaled up to accommodate 2.5 g of crude reaction products containing a mixture of the acetins. The solvent system ethyl acetate/n‐butanol/water 1:0.2:1 was used in all separation procedures. Mono‐, di‐ and triacetins were separated similarly in the semi‐preparative and preparative runs.     

Iron‐Catalyzed Friedel–Crafts Benzylation with Benzyl TMS Ethers at Room Temperature

Friedel–Crafts benzylations between unactivated arenes and benzyl alcohol derivatives are clean and straightforward processes to construct biologically useful di‐ and tri‐arylmethanes. We have established an efficient iron‐catalyzed Friedel–Crafts benzylation method at room temperature that uses benzyl TMS ethers as substrates, which are poorly reactive under common nucleophilic substitution conditions. The reaction seems to progress through iron‐catalyzed self‐condensation of the benzyl TMS ether to the corresponding dibenzylic ether. The use of excess arene relative to benzyl TMS ether produced mono‐benzylated arene (di‐ and tri‐arylmethane products), whereas the use of excess benzyl TMS ether versus arene provided bis‐benzylated arene (polyarylated products) in high yields and regioselectivities. In previous methods, the latter double Friedel–Crafts benzylations hardly proceed.     

Synthesis and Bioactivity of Novel N,N'-Diacylhydrazine Derivatives Containing Furan (Ⅱ)

Diacylhydrazines have been found as molting hormone analogs since RH‐5849 was reported as the first nonsteroidal ecdysone agonist in 1988. Optimizations on diacylhydrizines with benzoheterocycle containing oxygen were widely explored in recent years. In order to find novel compounds with high bioactivity, a series of mono‐ ( I ) and di‐acylhydrazine ( II ) derivatives containing furan were designed and synthesized. Their structures were confirmed by ¹H NMR, IR, elemental analyses and single crystal X‐ray diffraction analyses ( II ₇). The bioassay results showed that some of the mono‐acylhydrazine ( I ) derivatives exhibited good larvicidal activity against Culex pipiens pallens at 10 mg/L and better than those of di‐acylhydrazines ( II ). Generally, the anti‐tumor activity of di‐acylhydrazines ( II ) was better than that of mono‐acylhydrazines ( I ).     

Synthesis and characterization of diphenylmethyltin(IV) mono‐, di‐, and trichloroacetate

Diphenylmethyltin(IV) mono‐, di‐, and trichloroacetate have been synthesized and characterized by infrared, ¹H, ¹³C, ¹¹⁹Sn NMR, and mass spectroscopy. Infrared spectroscopy indicates that the prepared organotin carboxylates possess chain polymer structures. NMR data show that the mono‐ and dichloro derivatives do not retain the solid state structure in solution. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:18–22, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10059     

Functionalization of Quinoxalines by Using TMP Bases: Preparation of Tetracyclic Heterocycles with High Photoluminescene Quantum Yields

Tetracyclic heterocycles that exhibit high photoluminescence quantum yields were synthesized by anellation reactions of mono‐, di‐, and trifunctionalized 2,3‐dichloroquinoxalines. Thus, treatment of 2,3‐dichloroquinoxaline with TMPLi (TMP=2,2,6,6‐tetramethylpiperidyl) allows a regioselective lithiation in position 5. Quenching with various electrophiles (iodine, (BrCl₂C)₂, allylic bromide, acid chloride, aryl iodide) leads to 5‐functionalized 2,3‐dichloroquinoxalines. Further functionalization in positions 6 and 8 can be achieved by using TMPLi or TMPMgCl ? LiCl furnishing a range of new di‐ and tri‐functionalized 2,3‐dichloroquinoxalines. The chlorine atoms are readily substituted by anellation with 1,2‐diphenols or 1,2‐dithiophenols leading to a series of new tetracyclic compounds. These materials exhibit strong, tunable optical absorption and emission in the blue and green spectral region. The substituted O‐heterocyclic compounds exhibit particularly high photoluminescence quantum yields of up to 90 %, which renders them interesting candidates for fluorescence imaging applications.     

Synthesis and characterization of fluid 1,3‐benzoxazine monomers and their thermally activated curing

Novel mono‐ and difunctional aliphatic oxyalcohol‐based benzoxazines have been synthesized and characterized in detail. Molecular structures of the monomers were investigated by spectral analysis. The obtained benzoxazine monomers exhibit fluidic behavior, which makes them particularly useful for many applications compared to other traditional benzoxazines. Differential scanning calorimetry was used to monitor the thermal crosslinking behavior of synthesized monomers. Mono‐ and bifunctional benzoxazine monomers exhibited low curing exhothermic peak with the onset around 173 and 180 °C, respectively. Relatively, low ring‐opening polymerization temperature was due to the hydroxyl groups present in the structure of the monomers. The hydrogen bonding of hydroxyl groups may cause alignment of the monomers in the liquid state. Thermal stabilty of the polybenzoxazines was studied by thermogravimetric analysis. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

Chemical Functionalisation and Photoluminescence of Graphene Quantum Dots

Chemical modification of graphene quantum dots (GQDs) can influence their physical and chemical properties; hence, the investigation of the effect of organic functional groups on GQDs is of importance for developing GQD–organic hybrid materials. Three peripherally functionalised GQDs having a third‐generation dendritic wedge (GQD‐ 2 ), long alkyl chains (GQD‐ 3 ) and a polyhedral oligomeric silsesquioxane group (GQD‐ 4 ) were prepared by the Cu^I‐catalysed Huisgen cycloaddition reaction of GQD‐ 1 with organic azides. Cyclic voltammetry indicated that reduction occurred on the surfaces of GQD‐ 1 – 4 and on the five‐membered imide rings at the periphery, and this suggested that the functional groups distort the periphery by steric interactions between neighbouring functional groups. The HOMO–LUMO bandgaps of GQD‐ 1 – 4 were estimated to be approximately 2 eV, and their low‐lying LUMO levels (<?3.9 eV) were lower than that of phenyl‐C₆₁‐butyric acid methyl ester, an n‐type organic semiconductor. The solubility of GQD‐ 1 – 4 in organic solvents depends on the functional groups present. The functional groups likely cover the surfaces and periphery of the GQDs, and thus increase their affinity for solvent and avoid precipitation. Similar to GQD‐ 2 , both GQD‐ 3 and GQD‐ 4 emitted white light upon excitation at 360 nm. Size‐exclusion chromatography demonstrated that white‐light emission originates from the coexistence of differently sized GQDs that have different photoluminescence emission wavelengths.     

From Alkanes to Carboxylic Acids: Terminal Oxygenation by a Fungal Peroxygenase

A new heme–thiolate peroxidase catalyzes the hydroxylation of n‐alkanes at the terminal position—a challenging reaction in organic chemistry—with H₂O₂ as the only cosubstrate. Besides the primary product, 1‐dodecanol, the conversion of dodecane yielded dodecanoic, 12‐hydroxydodecanoic, and 1,12‐dodecanedioic acids, as identified by GC–MS. Dodecanal could be detected only in trace amounts, and 1,12‐dodecanediol was not observed, thus suggesting that dodecanoic acid is the branch point between mono‐ and diterminal hydroxylation. Simultaneously, oxygenation was observed at other hydrocarbon chain positions (preferentially C2 and C11). Similar results were observed in reactions of tetradecane. The pattern of products formed, together with data on the incorporation of ¹⁸O from the cosubstrate H₂¹⁸O₂, demonstrate that the enzyme acts as a peroxygenase that is able to catalyze a cascade of mono‐ and diterminal oxidation reactions of long‐chain n‐alkanes to give carboxylic acids.     

Convenient Synthesis of Pyrrole‐ and Indolecarboxylic Acid tert‐Butylesters

Abstract

The tert‐butylesters of pyrrole‐ and indolecarboxylic acids are readily accessed by reacting the appropriate carboxylic acids with N,N‐dimethylformamide di‐tert‐butyl acetal.     

Mono‐ and Binuclear Dimethylthallium(III) Complexes with o‐Benzoquinone‐TTF‐o‐Benzoquinone Ligand; Synthesis,Spectroscopy and X‐ray Study

The new mono‐ and binuclear semiquinonato dimethylthallium complexes (Q‐TTF‐SQ)TlMe₂ ( 1 ) and Me₂Tl(SQ‐TTF‐SQ)TlMe₂ ( 2 ) based on di‐o‐quinone with tetrathiafulvalene (TTF) bridge, 4,4′,7,7′‐tetra‐tert‐butyl‐2,2′‐bis‐1,3‐benzodithiol‐5,5′,6,6′‐tetraone Q‐TTF‐Q, were synthesized by the reaction between corresponding mono‐ and di‐sodium semiquinonates (Q‐TTF‐SQ)Na and Na(SQ‐TTF‐SQ)Na and one or two equivalents of Me₂TlCl, respectively. The same products could be obtained by the interaction of Q‐TTF‐Q with one or two equivalents of Me₃Tl. Complexes 1 and 2 were characterized by IR and electronic absorption spectroscopy, EPR, and magnetic measurements. The molecular structures of 1 and 2 were determined by single‐crystal X‐ray diffraction. It was found that mono‐semiquinonato derivative 1 partially disproportionates into Q‐TTF‐Q and binuclear complex 2 in THF solution. According to variable temperature magnetic susceptibility measurements and EPR data, compound 1 reveals paramagnetic behavior with an S = 1/2 state in the range 50–300 K, whereas compound 2 has an S = 0 ground state as the consequence of antiferromagnetic coupling between semiquinonato moieties realized through the TTF‐bridge.     

N‐Carboxyanhydride Polymerization of Glycopolypeptides That Activate Antigen‐Presenting Cells through Dectin‐1 and Dectin‐2

The C‐type lectins dectin‐1 and dectin‐2 contribute to innate immunity against microbial pathogens by recognizing their foreign glycan structures. These receptors are promising targets for vaccine development and cancer immunotherapy. However, currently available agonists are heterogeneous glycoconjugates and polysaccharides from natural sources. Herein, we designed and synthesized the first chemically defined ligands for dectin‐1 and dectin‐2. They comprised glycopolypeptides bearing mono‐, di‐, and trisaccharides and were built through polymerization of glycosylated N‐carboxyanhydrides. Through this approach, we achieved glycopolypeptides with high molecular weights and low dispersities. We identified structures that elicit a pro‐inflammatory response through dectin‐1 or dectin‐2 in antigen‐presenting cells. With their native proteinaceous backbones and natural glycosidic linkages, these agonists are attractive for translational applications.