Synthesis of 2-thioxo-3-benzothiazolineacetonitrile and related products

Attempts to thermally rearrange 2-benzothiazolylthioacetonitrile ( 1) to the titled compound 8 failed. The reaction of 3-chloromethyl-2-benzothiazolinethione with potassium cyanide in dimethylformamide (DMF) or dimethylsulfoxide (DMSO) at 25-30° afforded 8 in 98% yield. Whereas replacing the DMF or DMSO solvent with acetone furnished the unexpected sulfide 9 in 92% yield. Substituting 3-chloromethyl-2-benzoxazoline-thione as the electrophile in the same reaction gave the sulfide 10 in 95% yield. Possible mechanisms and supporting nmr data are discussed.     

脂肪酶直接与硅胶混合催化无溶剂酯化反应的研究

用硅胶作为载体，以癸酸与己醇的酯化反应作为模型，将脂肪酶和底物直接与硅胶混合，用于无溶剂体系催化酯化反应．结果表明体系中水的含量、底物用量比以及反应时间均对酯化反应有较大影响．在该体系中，脂肪酶催化酯合成反应的速度显著增加，反应2h后．转化率可以达到90％以上．而且沉积在硅胶上的脂肪酶可以反复使用多次．     

Copper-free click chemistry with the short-lived positron emitter fluorine-18

The copper-free strain-promoted click chemistry between (18)F-labeled aza-dibenzocyclooctyne [(18)F]FB-DBCO and various azides is described. [(18)F]FB-DBCO was prepared in 85% isolated radiochemical yield (decay-corrected) through acylation of amino aza-dibenzocyclooctyne 1 with N-succinimidyl 4-[(18)F]fluorobenzoate ([(18)F]SFB). [(18)F]FB-DBCO showed promising radiopharmacological profil with fast blood clearance as assessed with dynamic small animal PET studies. Metabolic stability of [(18)F]FB-DBCO was 60% of intact compound after 60 min post injection in normal Balb/C mice and blood clearance half-life was determined to be 53 s based on the time-activity-curve (TAC). Copper-free click chemistry was performed with various azides at low concentrations (1-2 μM) which differed in their structural complexity in different solvents (methanol, water, phosphate buffer and in bovine serum albumin (BSA) solution). Reaction proceeded best in methanol (>95% yield after 15 min at room temperature), whereas reaction in BSA required longer reaction times of 60 min and 40 °C upon completion.     

Studies on regioselective acylation of cellulose with bulky acid chlorides

The regioselective esterification of cellulose by reaction with bulky acyl halides including pivaloyl chloride, adamantoyl chloride and 2,4,6-trimethylbenzoyl chloride was studied. Functionalization conditions to achieve a given degree of substitution (DS) and the resulting ester substitution pattern were described in detail. One- and two-dimensional NMR spectroscopy techniques were used to confirm the structure of the esters obtained. We compared the effects on substitution of using different esterifying reagents and solvent systems including DMAc/LiCl, DMSO/TBAF, and ionic liquids (ILs).     

蔗糖酯的合成研究进展

综述了蔗糖酯的合成方法及工艺的研究进展,并对其反应机理进行了阐述.蔗糖酯的合成方法主要有四种:溶剂法、微乳化法、无溶剂法以及酶催化法.溶剂法采用DMF或DMSO为溶剂,但是这两种溶剂均有毒,限制了蔗糖酯在食品等行业的应用.微乳化法采用丙二醇或水代替溶剂法所使用的有毒溶剂,并加入乳化剂,使反应体系近似为均相体系.无溶剂法则是通过在反应体系中加入乳化剂或表面活性剂等使熔融相成均一相,反应平稳.但是一般无溶剂法反应温度较高,反应不易进行,产率低,且产品质量得不到保证.酶催化合成法是一种新的生物合成方法,采用生物酶代替传统的催化剂合成蔗糖酯,该法催化活性高、反应条件温和、选择性强、产物易分离等优点.文中还对蔗糖酯粗品的纯化工艺进行了介绍.     

Microwave assisted mild, rapid, solvent-less, and catalyst-free chemoselective N-tert-butyloxycarbonylation of amines

Microwave assisted simple, rapid, solventless, and catalyst-free chemoselective method for the protection of amino group in aromatic, aliphatic, heterocyclic, aralkyl amines, phenyl hydrazine, and amino acid esters in good to excellent isolated yield (83-98%) in short reaction time (2-12 min) has been reported.     

Separation of the insecticidal pyrethrin esters by capillary electrochromatography

A simple, rapid technique for the direct separation and quantification of the six insecticidally active pyrethrin esters in typical extracts and commercial formulations by capillary electrochromatography (CEC) has been described. The separation of the pyrethrin esters was achieved by optimizing several parameters including the length of stationary phase, the mobile phase composition and column temperature. The mobile phase composition had the most pronounced effect toward resolving these structurally similar compounds. A ternary mobile phase composed of acetonitrile-aqueous buffer-tetrahydrofuran (55:35:10) provided the elutropic solvent strength needed to resolve the six esters from an extract mixture in under 16 min. A 25 cm packed bed of Hypersil 3 microm C18 stationary phase was used with the ternary mobile phase at 25 degrees C and 30 kV voltage. These conditions also yielded excellent separation of the pyrethrin esters in two different commercially available insecticidal formulations. In addition, the developed CEC method was shown to be a fast and easy way of quantifying the amount of these esters in typical pyrethrin formulations.     

Preparation of 5-Hydroxymethylfurfural from Cellulose via Fast Depolymerization and Consecutively Catalytic Conversion

The conversion of cellulose to 5-hydroxymethylfurfural (HMF) has been investigated by a one-pot consecutive reaction. At first, cellulose was depolymerised into glucose via a fast degradation of cellulose in molten ZnCl2 in the presence of hydrochloric acid, and the yield of glucose is 75% in 120 s at reaction temperature of 95 oC. Then, DMSO was used as solvent and different kinds of metal chloride were added as catalysts, and the conversion was carried out continuously at 110-130 oC for 0.5-4 h. The yield of HMF was 53% when CrCl3 were used as catalyst. The one-pot two steps conversion was carried out at atmosphere pressure, and it is a simple route to prepare HMF from lignocellulosic feedstock on a large scale.     

Metal-free catalytic C-Si bond formation in an aqueous medium. Enantioselective NHC-catalyzed silyl conjugate additions to cyclic and acyclic α,β-unsaturated carbonyls

A metal-free method for enantioselective conjugate addition of a dimethylphenylsilyl group to α,β-unsaturated carbonyls is reported. Transformations are catalyzed by a chiral N-heterocyclic carbene (NHC), performed in an aqueous solution (3:1 mixture of water and tetrahydrofuran) and are operationally simpler to perform than the NHC-Cu-catalyzed variant. The chiral catalyst is generated from an enantiomerically pure imidazolinium salt (prepared in three steps) and a common organic amine base (dbu). NHC-catalyzed processes proceed with 5.0-12.5 mol % catalyst loading at 22 °C within 1-12 h, affording the desired β-silyl carbonyls in 85:15 to >98:2 enantiomeric ratio and in 50% to >98% yield. Cyclic enones or lactones and acyclic α,β-unsaturated ketones, esters, and aldehydes can be used as substrates.     

Oxidative dimerization of primary alcohols to esters catalyzed by iridium complexes

Primary alcohols undergo efficiently oxidative dimerization by iridium complexes under air without any solvent to form esters in fair to good yields. For instance, the reaction of 1-dodecanol in the presence of [IrCl(coe)₂]₂ (3 mol %) at 95 °C for 15 h produced dodecyl dodecanoate in 91% isolated yield. This is the first successful Ir-catalyzed oxidative dimerization of primary alcohols to esters using air as an oxidant. Various primary alcohols are converted to the corresponding esters in fair to good yields.     

Formation of vinyl-, vinylhalide- or acyl-substituted quaternary carbon stereogenic centers through NHC-Cu-catalyzed enantioselective conjugate additions of Si-containing vinylaluminums to β-substituted cyclic enones

A catalytic method for enantioselective conjugate addition (ECA) of Si-containing vinylaluminum reagents to β-substituted cyclopentenones and cyclohexenones is described. Reactions are promoted by 1.0-5.0 mol % of a bidentate NHC-Cu complex, which is prepared from air-stable CuCl(2)?2H(2)O and used in situ, and typically proceed to completion within 15-20 min. The requisite vinylmetals are generated efficiently by a site-selective hydroalumination of an alkyne with dibal-H. The desired products, containing a quaternary carbon stereogenic center, are obtained in 48-95% yield after purification and in 89:11 to >98:2 enantiomer ratio (er). The vinylsilane moiety within the products can be functionalized to afford acyl, vinyliodide, or desilylated alkenes in 67% to >98% yield and with >90% retention of the alkene's stereochemical identity. The utility of the catalytic process is illustrated in the context of a concise enantioselective synthesis of riccardiphenol B.     

Polymer-supported O-methylisourea: a new reagent for the O-methylation of carboxylic acids

[reaction: see text] A solid-supported O-methylisourea reagent has been prepared in one step starting from commercially available solid-supported carbodiimide. The isourea reagent has been successfully used for the preparation of methyl esters from the corresponding carboxylic acids. The crude products obtained after resin filtration and solvent evaporation are generally obtained in >98% purity.     

Novel,efficient,and green procedure for the synthesis of 1,5-benzodiazepines catalyzed by MgBr_2 in aqueous media

MgBr_2 performs as a novel catalyst for the synthesis of various 1,5-benzodiazepine derivatives from wide range of substituted ophenylenediamines and various ketones in good to excellent isolated yields(93-98%)using water as solvent at ambient temperature.Several solvents were examined for this reaction;however,in terms of reaction yield and time,water was found to be the optimum solvent.The remarkable advantages offered by this method are easily and inexpensive available catalyst,simple procedure,mild c...     

离子液体中磺化无定形炭催化菊糖制备5-羟甲基糠醛

研究了以1-丁基-3-甲基咪唑氯盐([Bmim]Cl)离子液体作溶剂,磺化无定形炭为催化剂催化菊糖脱水制5-羟甲基糠醛(HMF)的反应.考察了溶剂、水量、反应温度、反应时间和催化剂用量对HMF收率的影响.实验结果表明,反应温度为100°C,反应时间60min,R=5(R为水的物质的量与菊糖中所含果糖单位的物质的量的比值),m(催化剂):m(菊糖)=1:3时,HMF的收率可达50%.     

An efficient and solvent-free one-pot synthesis of 1,4-dihydropyridines under microwave irradiation

An efficient synthesis of 1,4-dihydropyridines using lanthanum oxide as a catalyst from aldehydes,β-ketoester and ammonium acetate without solvent under the irradiation of microwave is described.Compared with the classical Hantzsch reaction,this new method has the advantage of good yield(90-98%) and short reaction time(40-80 s).     

Rhodium-catalyzed 1,4-addition of alkenylzirconocene chlorides to electron deficient alkenes

The 1,4-conjugated addition of alkenylzirconocene chloride complexes to α,β-enones, α,β-enoic acid esters, and α,β-enoic acid amides can be efficiently achieved by the use of [RhCl(cod)]₂ catalyst. A high diastereoselectivity (95% yield, 90% de) was obtained through the reaction of α,β-enoic acid amide derived from Oppolzer's sultam and 2-butenoyl chloride, while the use of Evans' chiral oxazolidinone as a chiral auxiliary in place of Oppolzer's sultam gave a poor diastereoselectivity (98% yield, 26% de).     

Development of a new Lewis acid-catalyzed [3,3]-sigmatropic rearrangement: the allenoate-Claisen rearrangement

A new Lewis acid-catalyzed Claisen rearrangement has been developed that allows the stereoselective construction of beta-amino-alpha,beta,epsilon,zeta-unsaturated-gamma,delta-disubstituted esters from simple allylic amines and allenoate esters. This reaction, which is contingent upon the use of Lewis acid, can be conducted with a range of metal salts (Yb(OTf)3, AlCl3, Sn(OTf)2, Cu(OTf)2, MgBr2.Et2O, FeCl3, Zn(OTf)2) with catalyst loadings as low as 5 mol %. This catalytic process provides access to a diverse range of beta-amino-alpha,beta,epsilon,zeta-unsaturated-gamma,delta-disubstituted esters in high yield and with excellent levels of diastereoselectivity for a series of allyl pyrrolidines (R1 = H, Me, i-Pr, Ph, NR2 = pyrrolidine, piperidine, NMe2; >/=81% yield, >/=94:6 syn:anti) and allenoate esters (R2 = H, Me, i-Pr, Ph, allyl, NPht, Cl; >/=75% yield, >/=91:9 syn:anti). The capacity of this new Claisen rearrangement to provide catalytic access to elusive structural motifs has also been demonstrated in the stereospecific formation of quaternary carbon bearing frameworks arising from geranyl- and neryl pyrrolidine (>/=93% yield, >98:2 dr).     

Enzymatic synthesis and analytical monitoring of terpene ester by <Superscript>1</Superscript>H NMR spectroscopy

Terpene esters of fatty acids have potential applications in food, cosmetic, and pharmaceutical industries. The present study focuses on the synthesis of terpene esters of long chain fatty acids catalyzed by Candida antarctica lipase B. Different parameters like temperature, solvent, and enzyme concentration for the esterification of terpene alcohols (geraniol and citronellol) with oleic acid were studied. Maximum conversion (98 %) was found for both terpene esters at 60°C in 2,2,4-trimethylpentane as well as in dry hexane and around 95–97 % in other tested solvents. The reaction was also carried out using stearic and linoleic acid in hexane to study the effects of unsaturation in the substrate in which stearic acid showed the maximum conversion. The reaction was monitored by ¹H nuclear magnetic resonance spectroscopy. Using the peak integration values of methylene protons of terpene and terpene ester of δ = 3.6 and 4.0 for citronellol and δ = 4.2 and 4.6 for geraniol, respectively, percentage conversions of each of the esters were calculated.     

Acid-induced dimerization of imidates derived from glycine: Synthesis of methyl N-(1,2,5-trisubstituted-4-imidazoyl)glycinates

A number of N-(1,2,5-trisubstituted-4-imidazoyl)-glycinates 4 were prepared in 60–95% yield from imidates 1 derived from α-amino esters by cyclodimerization without solvent at 70°C in acetic acid medium. According to this process, the reaction of imidate 1a as a 1,3-dipole generated in situ by thermal 1,2-prototropy with the free ethyl benzimidate as the dipolarophile has been investigated for the first time and gave directly the methyl imidazole-4-carboxylate in moderate yield by regioselective [3 + 2] cycloaddition. © 1996 John Wiley & Sons, Inc.     

微波辐射法合成2-(4-取代苯乙烯基)苯并噻唑

甲基苯并噻唑;芳香醛;微波辐射法合成2-(4-取代苯乙烯基)苯并噻唑