Recyclable ligand-free mesoporous heterogeneous Pd catalysts for Heck coupling

Ligand-free Pd-MCM41 catalysts are highly active in the Heck coupling of bromoarenes including deactivated bromo derivatives to give coupled products in high yields with high selectivities without the need to exclude air or moisture. The catalyst samples exhibit unprecedented stability among heterogeneous catalysts and can be reused at least 20 times to achieve complete conversion without any additional activation treatment.     

A novel method for bromodecarboxylation of α,β-unsaturated carboxylic acids using catalytic sodium nitrite

A first novel synthetic utility of catalytic sodium nitrite in combination with aqueous HBr, for bromo decarboxylation of α,β-unsaturated carboxylic acid is described. α,β-Unsaturated carboxylic acid compounds successfully converted into corresponding bromo compounds. The advantages of this protocol are shorter reaction time and moderate to good yields.     

Unsymmetric pyrrole, thiophene, and furan-conjugated comonomers prepared using azomethine connections: potential new monomers for alternating homocoupled products

Unsymmetric comonomers consisting of thiophene, pyrrole, and furan heterocycles were prepared using azomethine bonds. Photophysical investigation of the novel pi-donor-donor-donor segmented compounds revealed that their singlet excited state is only partially deactivated by internal conversion unlike their all-thiophene azomethine analogues. Temperature-dependent steady-state and time-resolved emission studies demonstrated that the unsymmetric compounds deactivated efficiently their singlet excited state by intersystem crossing to populate the triplet manifold. This lower energy state is rapidly deactivated by nonradiative self-quenching. The comonomers and their anodically prepared conjugated homocoupled products are both electrochemically active, resulting in new compounds that can be mutually oxidized and reduced. Meanwhile, the oxidation potentials of the coupled products are shifted by up to 400 mV to more cathodic potentials relative to their corresponding comonomers, confirming their increased degree of conjugation.     

The proton magnetic resonance spectra of some disubstituted acetophenones

An accurate measurement of the chemical shifts and the coupling constants of some disubstituted acetophenones has been made. The acetophenones studied contained nitro, bromo or amino groups substituted in either the 3,4 or 2,5 positions. For compounds with no substituent adjacent to the acetyl group, the chemical shifts and the coupling constants estimated by the simple additivity of the substituent increments were found to be in reasonable agreement with the experimental values. The two nitro, bromo derivatives substituted in positions 2 and 5 probably prefer the conformer in which the proton H-6 is adjacent to the acetyl methyl group whilst the 3,4-disubstituted bromo, nitro and bromo, amino derivatives prefer the conformer in which the H-6 proton is adjacent to the carbonyl group.     

Titanocene(III) chloride mediated radical-induced addition to Baylis-Hillman adducts: synthesis of (E)- and (Z)-trisubstituted alkenes and alpha-methylene/arylidene delta-lactones

Baylis-Hillman adduct underwent smooth radical-induced condensation with activated bromo compounds and epoxides using titanocene(III) chloride (Cp2TiCl) as the radical generator. The reactions of activated bromo compounds with 3-acetoxy-2-methylene alkanoates provided (E)-alkenes exclusively, whereas similar reactions with 3-acetoxy-2-methylenealkanenitriles led to (Z)-alkenes as the major product. The reactions of epoxides with Baylis-Hillman adduct furnished alpha-methylene/arylidene-delta-lactones in good yield via addition followed by in situ lactonization.     

Enantiopure Trioxadecalin Derived Liquid Crystals: Influence of the Nature of the Phenyl Substituent on the Mesogenic Properties

Reaction of pseudo‐glucal 1 with Grignard reagents derived from 1‐bromo‐4‐(trimethylsilyloxy)benzene, 1‐bromo‐4‐methoxybenzene, 1‐bromo‐4‐methoxymethoxybenzene, 1‐bromo‐4‐dimethylaminobenzene, in the presence of a catalytic amount of NiCl₂(dppe), gives the corresponding unsaturated β‐C‐aryl glycosides 2. Desilylation and hydrogenation of 2 leads to β‐C‐aryl glycosides 4, which can be used as chiral precursor compounds in the synthesis of chiral liquid crystals. Combination of 4 with arylaldehydes leads to compounds 5–7, whereas reaction with p‐alkoxysubstituted phenylboronic acids gives the trioxaboradecalins 8–11. The mesogenic properties of these compounds are strongly influenced by the nature of the substituent on the phenyl ring in the molecule.     

A novel and facile one‐pot synthesis of pyridylselenium compounds through selective bromine–magnesium exchange with isopropylmagnesium halide

One‐pot synthesis of various unsymmetrical 2‐bromo‐5‐pyridylselenium compounds has been carried out under non‐cryogenic conditions by selective single bromine–magnesium exchange of 2,5‐dibromopyridine using isopropylmagnesium chloride. This exchange gives 2‐bromo‐5‐pyridylmagnesium chloride, which upon the insertion of elemental selenium followed by the treatment with alkyl halide gives the title compounds in good yield. This exchange has also been extended towards bromine–magnesium exchange of 2‐bromopyridine for the improved synthesis of 2‐pyridylselenium compounds. The molecular structure of 2‐bromo‐5‐selenopyridyltribromomethane has been examined by single crystal X‐ray diffraction. This compound crystallizes in the monoclinic space group P2₁/n. From the molecular structure it was found that intermolecular BrBr, NSe and SeBr interactions control its crystal packing. Copyright © 2005 John Wiley & Sons, Ltd.     

Effect of terminal aryl rings of liquid crystal trimers on liquid crystalline properties

Liquid crystalline properties of five series of biphenyl derivatives connected with p-nitrophenyl, phenyl, 2-naphthyl, 9-phenathryl and bromo as the terminal groups via flexible spacers were studied. All the compounds exhibited nematic phase. The nematic–isotropic or isotropic–nematic transition properties resulted in an odd–even effect as the length of the spacers was varied, in which the even members exhibited higher values, for the compounds with p-nitrophenyl, phenyl, 2-naphthyl and 9-phenanthryl groups, while the transitional properties of the compounds substituted with bromo atom as the terminal group instead of the aryl groups did not show such odd–even effect. These results suggest that the aryl rings, such as p-nitrophenyl, phenyl, 2-naphthyl and 9-phenanthryl groups, play a role of mesogen while the terminal bromo atom does not. The effect of the terminal aryl rings on the liquid crystalline properties will be reported.     

Enantioselective Palladium‐Catalyzed Cross‐Coupling of α‐Bromo Carboxamides and Aryl Boronic Acids

We herein report an enantioselective palladium‐catalyzed cross‐coupling between α‐bromo carboxamides and aryl boronic acids, generating a series of chiral α‐aryl carboxamides in good yields and excellent enantioselectivities. The development of a chiral P,P=O ligand was critical in overcoming the second transmetalation issue and allows the first asymmetric palladium‐catalyzed coupling of α‐bromo carbonyl compounds.     

Applications of deactivated GC columns for analysis of nitrogen-containing chemicals related to the chemical weapons convention

Nitrogen-containing chemicals are one of the important families of compounds relevant to the purposes of the Chemical Weapons Convention (CWC). Several applications, using various injection modes, of new deactivated columns specially designed for basic compounds are presented. These columns prove remarkably well-suited to the gas chromatographic (GC) analysis of the chemicals of interest, even to underivatized amino-alcohols, whose analysis on conventional GC columns is often difficult and hindered by poor resolution and high detection limits. Such a deactivated phase can even replace the typical GC phases used for CWC verification purposes.     

Reaction of Polyfluoro-3-chloro(bromo)-1-butenes with Sodium Hypohalites and Properties of Epoxides Derived Therefrom

Epoxidation of 3-chloro(bromo)heptafluoro-1-butenes and 3,4-dichlorohexafluoro-1-butene with aqueous solutions of sodium hypohalites is accompanied by cleavage of the carbon skeleton at the double bond and formation of polyfluorocarboxylic acid sodium salts as by-products. 3-Chloro(bromo)-1,2-epoxy- heptafluoro- and 3,4-dichloro-1,2-epoxyhexafluorobutanes were synthesized and subjected to isomerization into carbonyl compounds by the action of cesium fluoride or antimony pentafluoride.     

Bromination of Anisoles Using N‐Bromophthalimide: A Synthetic and Kinetic Approach

N‐Bromophthalimide (NBP)‐triggered bromination of aromatic compounds has been studied in the presence of aqueous acetic acid. Reaction Kinetics indicated first order in [NBP] and zero order in [Anisole]. The reactions afforded very good yields of corresponding bromo derivatives under kinetic conditions. The mechanism of the reaction is explained through the formation of acetyl hypobromite due to the interaction of NBP and acetic acid, which in turn reacts with anisole to afford a bromo derivative of anisole.     

Heterocyclic silyl enol ether chemistry: Synthesis and reactivity of 3-trimethylsiloxyfuran and 3-trimethylsiloxythiophene

The preparation of the titte compounds is reported starting from the corresponding bromo derivatives.3-Trimethylsiloxyfuran gives rise easily to cycloadditions affording bicyclic tetrahydrofuranonic systems.     

Directed metalation and regioselective functionalization of 3-bromofuran and related heterocycles with NaHMDS

A mild and regioselective functionalization protocol for 3-bromofuran and analogs has been developed. Selective metalation and functionalization of C2 can be achieved as a result of the directing effect of the adjacent electron-withdrawing bromo group. In addition, the C5 position can also be selectively functionalized by blocking the C2 position via silylation or by simply controlling the reaction temperature. These functionalized compounds bearing a C3 bromo substituent may be further elaborated by utilizing a Suzuki–Miyaura cross-coupling procedure.     

Halogenated chamigrane sesquiterpenes from Laurencia okamurae

Three new halogenated chamigrane sesquiterpenes, laurokamin A (1), laurokamin B (2), and laurokamin C (3), and four known halogenated chamigrane sesquiterpenes, 10‐bromo‐α‐chamigrene (4), 10‐bromo‐β‐chamigrene (5), 2,10‐dibromo‐3‐chloro‐β‐chamigrene (6), and obtusane (7), were isolated from the marine red alga Laurencia okamurae collected from the coast of Rongcheng, China. The structures of these compounds were unambiguously identified by one‐ and two‐dimensional NMR and mass spectroscopic methods. The antimicrobial activity of compounds 1–3 was evaluated. Copyright © 2012 John Wiley & Sons, Ltd.     

Supported Tetramethylamonium Nitrate/Silicasulfuric Acid as a Useful Reagent for Nitration Aromatic Compounds Under Solvent‐Free Conditions

A variety of aromatic compounds are nitrated to the parent nitro aromatic compounds under solvent‐free conditions using supported tetramethylammonium nitrate/silicasulfuric acid as a useful reagent. This methodology is useful for nitration of activated and deactivated aromatic rings.     

Novel Synthesis and Antimicrobial Activity of 3‐Substituted 5‐bromo‐7‐methyl‐1,2,4‐triazolo‐[3,4‐b]‐benzothiazoles

4‐Methyl acetanilide ( 1 ) on treatment with bromine in acetic acid, followed by hydrolysis with dilute HCl/NaOH solution, yielded 2‐bromo‐4‐methyl aniline ( 2 ), which on treatment with sodium thiocyanate in acetic acid afforded 2‐amino‐4‐bromo‐6‐methyl benzothiazole ( 3 ). Compound 3 in ethylene glycol was heated at 150°C with 80% hydrazine hydrate to get 4‐bromo‐2‐hydrazino‐6‐methyl benzothiazole ( 4 ). This hydrazino compound 4 on heating with formic acid for 3 h yielded 4‐bromo‐2‐hydrazinoformyl‐6‐methyl benzothiazole ( 5 ). Same compound 4 when heated independently with formic acid for 6 h/urea for 3 h/carbon disulfide in alkali afforded 5‐bromo‐7‐methyl ( 6 )/5‐bromo‐3‐hydroxy‐7‐methyl ( 7 )/5‐bromo‐3‐mercapto‐7‐methyl ( 8 )‐1,2,4‐triazolo‐[3,4‐b]‐benzothiazoles, respectively. Compound 4 on heating with acetic acid/acetic anhydride gave acetyl benzothiazolyl derivative 9 , which on cyclization with orthophosphoric acid yielded 5‐bromo‐3,7‐dimethyl‐1,2,4‐triazolo‐[3,4‐b]‐benzothiazole ( 10 ). All these newly synthesized compounds were screened for antimicrobial activity against Escherichia coli (Gram ?ve), Bacillus subtilis (Gram +ve), Erwinia carotovora, and Xanthomonas citri using ampicillin, streptomycin, and penicillin as a standard for comparison.     

Highly Efficient Construction of Bisspirooxindoles Containing Vicinal Spirocenters through an Organocatalytic Modified Feist–Bénary Reaction

We have developed an organocatalytic modified Feist–Bénary reaction of cyclic dicarbonyl compounds, isatins and cyclic α‐bromo dicarbonyl compounds. This method affords bisspirooxindole‐fused dihydrofurans containing two vicinal spiro centers. To the best of our knowledge, employing cyclic α‐halo dicarbonyl compounds for the synthesis of bisspirooxindole‐fused dihydrofurans has not been previously reported.     

几种查耳酮的二阶非线性光学性质解析

合成了一系列的查耳酮衍生物,系统地测量了其ＳＨＧ（二次谐波产生）效率和截止吸以长,并用ＣＮＤＯ／Ｓ－ＣＩ方法计算了它们的二阶非线性光学系数β值。通过对这些化合物性质的分析发现：（１）取代基Ｂｒ不仅能有效地增强微观非线性能能有效地增强材料的宏观非线性效应。（２）取代基Ｂｒ有利于改善材料的透光性能的和热稳定性;（３）分子在晶体中的空间取向是影响材料宏观非线性的另一个重要因素。     

Effect of sodium naphthalenide, a key SET reagent, on trifluoroacetyl derivatives

Aromatic trifluoroacetyl derivatives on treatment with single electron transfer (SET) reagent, sodium naphthalenide, yield symmetrical defluorinated dimers, whereas for aliphatic trifluoroacetyl compounds the reaction usually fails. Investigations have been made for different substituents as well as for similar types of chloro and bromo compounds to establish the scope of the reaction.