新试剂2-[2-(6-甲基苯并噻唑)偶氮]-5-二乙氨基苯甲酸与铁(Ⅱ)显色反应的研究与应用

本文研究了新试剂２－［２－（６－甲基苯并噻唑）偶氮］－５－二乙氨基苯甲酸（６－Ｍｅ－ＢＴＡＥＢ）与Ｆｅ（Ⅱ）的显色反应。结果表明，在十二烷基硫酸钠存在下新试剂与Ｆｅ（Ⅱ）在弱酸性介质中形成稳定的蓝紫色络合物，其组成为Ｆｅ（Ⅱ）∶６－Ｍｅ－ＢＴＡＥＢ＝１∶２，最大吸收波长为６３５ｎｍ，表观摩尔吸光系数为１．１０×１０５Ｌ·ｍｏｌ－１·ｃｍ－１，Ｆｅ（Ⅱ）浓度在每２５ｍＬ０～１０μｇ范围内服从比尔定律。在ＮａＦ和硫脲存在下方法具有好的选择性。并可用于直接测定铝合金中微量的铁，结果满意。     

新试剂2（2—（6—甲基苯并噻唑）偶氮）—5—二乙氨基苯甲酸与铁（Ⅱ）显色…

本文研究了新试剂２－（２－（６－甲基苯并噻唑）偶氮）－５－二乙氨基苯甲酸（６－Ｍｅ－ＢＴＡＥＢ）与Ｆｅ（Ⅱ）的显色反应，结果表明，在十二烷基硫酸钠存在下新试剂与Ｆｅ（Ⅱ）在弱酸性介质中形成稳定的蓝紫色络合物，其组成为Ｆｅ（Ⅱ）：６－Ｍｅ－ＢＴＡＥＢ＝１：２，最大吸收波长为６３５ｎｍ，表观摩尔吸光系数为１．１０×１０＾５Ｌ．ｍｏｌ＾－１．ｃｍ＾－１，Ｆｅ（Ⅱ）浓度在每２５ｍＬ０～１０μｇ范围的内服从     

Syntheses and Magnetic Properties of Cu（Ⅱ）－RE（Ⅲ） Heterobinuclear Complexes with N，N′－Bis（3－carboxyisalicylidene）－trimethylenediamine

ＳｙｎｔｈｅｓｅｓａｎｄＭａｇｎｅｔｉｃＰｒｏｐｅｒｔｉｅｓｏｆＣｕ（Ⅱ）－ＲＥ（Ⅲ）ＨｅｔｅｒｏｂｉｎｕｃｌｅａｒＣｏｍｐｌｅｘｅｓｗｉｔｈＮ，Ｎ′－Ｂｉｓ（３－ｃａｒｂｏｘｙｉｓａｌｉｃｙｌｉｄｅｎｅ）－ｔｒｉｍｅｔｈｙｌｅｎｅｄｉａｍｉｎｅＴＡ...     

活泼配盐[(μ-RE)(μ-E′)Fe_2(CO)_6][Et_3NH][E,E′=S,Se]的亲电反应研究——蝶状Fe_2SSe及Fe_2Se_2簇合物的合成及表征

本文由［（μｔＢｕＳ）（μＣＯ）Ｆｅ２（ＣＯ）６］［Ｅｔ３ＮＨ］和硒粉形成的［（μｔＢｕＳ）（μＳｅ）Ｆｅ２（ＣＯ）６］［Ｅｔ３ＮＨ］，分别与溴化苄，二碘甲烷及邻一、间一、对一双（溴甲基）苯反应，合成了蝶状Ｆｅ２ＳＳｅ单簇物（μｔＢｕＳ）（μＰｈＣＨ２Ｓｅ）Ｆｅ２（ＣＯ）６（３ａ）和双簇物［（μｔＢｕＳ）Ｆｅ２（ＣＯ）６］２（μＳｅＺＳｅμ）［Ｚ＝ＣＨ２，ｏ．ｍ．ｐ双（亚甲基）苯］（４ａｄ）。类似地，由［（μＰｈＳｅ）（μＣＯ）Ｆｅ２（ＣＯ）６］［Ｅｔ３ＮＨ］和硫粉或硒粉所形成的［（μＰｈＳｅ）（μＳ）Ｆｅ２（ＣＯ）６］［Ｅｔ３ＮＨ］或［（μＰｈＳｅ）（μＳｅ）Ｆｅ２（ＣＯ）６］［Ｅｔ３ＮＨ］分别与对一双（溴甲基）苯反应合成了蝶状Ｆｅ２ＳＳｅ和Ｆｅ２Ｓｅ２双簇物［（μＰｈＳｅ）Ｆｅ２（ＣＯ）６］２［μＳ（ｐＣＨ２Ｃ６Ｈ４ＣＨ２）Ｓμ］（５ａ）及［（μＰｈＳｅ）Ｆｅ２（ＣＯ）６］２［μＳｅ（ＰＣＨ２Ｃ６Ｈ４ＣＨ２）Ｓｅμ］（５ｂ）。所有产物均经元素分析、ＩＲ和１ＨＮＭＲ表征。     

铁（Ⅱ、Ⅲ）、钴（Ⅱ）、镍（Ⅱ）、铜（Ⅱ）－MBTAE配合物的反相高效液相色谱分离和测定

本文报道了以２－（６－甲基－２－苯并噻唑偶氮）－５－二乙氨基酚（ＭＢＴＡＥ）作柱前衍生化试剂，在ＳｐｈｅｒｉｓｏｒｂＣ＿８柱上，以甲醇：水＝８０：２０（Ｖ／Ｖ），含２ｍｍｏｌ／ＬＬｉ＿２ＳＯ＿４和１０ｍｍｏｌ／ＬｐＨ５．０醋酸盐缓冲溶液作流动相，反相高效液相色谱分离和测定了Ｆｅ￣（２＋）、Ｃｏ￣（２＋）、Ｎｉ￣（２＋）和Ｃｕ￣（２＋）。各金属离子的检出限（Ｓ／Ｎ＝３）分别为（ｐｇ）：Ｆｅ￣（２＋）６．４０，Ｃｏ￣（２－）１．３８，Ｎｉ￣（２＋）４．４７，Ｃｕ￣（２＋）７．２８。方法用于欧洲标准局，黑麦草标样的分析，所得结果与标准值相符。     

用Mo（Ⅲ）络合物分裂N_2分子

用Ｍｏ（Ⅲ）络合物分裂Ｎ_２分子麻省理工学院的Ｃ．Ｅ．Ｌａｐｌａｚａ和Ｃ．Ｃ．Ｃｕｍｍｉｎｓ用配位数为３的Ｍｏｔ（Ⅲ）络合物Ｍｏ（ＮＲＡｒ）３［Ｒ＝Ｃ（ＣＤ３）２ＣＨ３；Ａｒ＝３，５－Ｃ６Ｈ３Ｍｅ２（Ｍｅ，－ＣＨ３）与Ｎ２反应，实现了将Ｎ２分子裂开还?..     

金属键有机化合物的研究──非对称型η~5－取代环戊二烯基三羰基钼（钨）金属单键化合物的合成及表征

通过η５－Ｒ~１Ｃ＿５Ｈ＿４（ＣＯ）＿３ＭＮａ与η~５－Ｒ~２Ｃ＿５Ｈ＿４（ＣＯ）＿３ＭＮａ（Ｍ＝Ｍｏ，Ｗ）以及η~５－Ｒ~１Ｃ＿５Ｈ＿４（ＣＯ）＿３ＭｏＮａ与η~５－Ｒ~２Ｃ＿５Ｈ＿４（ＣＯ）＿３ＷＮａ在Ｆｅ＿２（ＳＯ＿４）＿３醋酸水溶液作用下的交叉氧化偶联反应，合成了７个新的非对称型金属单键化合物η~５－Ｒ~１Ｃ＿５Ｈ＿４（ＣＯ）－３Ｍｏ─Ｍｏ（ＣＯ）＿３Ｃ＿５Ｈ＿４Ｒ~２－η~５（Ｒ~１，Ｒ~２：Ｃ（Ｏ）Ｍｅ，ＣＯ２Ｅｔ），η５－Ｒ１Ｃ５Ｎ４（ＣＯ）３Ｗ─Ｗ（ＣＯ）３Ｃ５Ｈ４Ｒ２－η５（Ｒ１，Ｒ２：Ｃ（Ｏ）Ｍｅ，ＣＯ２Ｅｔ；Ｈ，ＣＯ２Ｅｔ）和η５－Ｒ１Ｃ５Ｈ４（ＣＯ）３Ｍｏ─Ｗ（ＣＯ）３Ｃ５Ｈ４Ｒ２－η５（Ｒ１，Ｒ２：Ｃ（Ｏ）Ｍｅ，Ｈ；Ｅｔ，Ｃ（Ｏ）Ｍｅ；Ｃ（Ｏ）Ｍｅ，ｎ－Ｂｕ；ＣＯ２Ｍｅ，ｎ－Ｂｕ）．用Ｃ／Ｎ分析、ＩＲ、１ＨＮＭＲ和ＭＳ表征了它们的结构，并对该氧化偶联反应的特点进行了讨论．     

双缓血氨二乙三胺五乙酸酰胺钆,镱螯合物的合成及其弛豫性能

缓血氨（Ｔｒｉｓ，三羟甲基氨基甲烷）修饰多氨多羧酸（二乙三胺五乙酸，ＤＴＰＡ和乙二胺四乙酸，ＥＤＴＡ）得到两种新的双酰胺型氨羧衍生物配体ＤＴＰＡВＴｒｉｓ和ＥＤＴＡＢＴｒｉｓ，并合成了它们的Ｇｄ３＋，Ｙｂ３＋，Ｍｎ２＋，Ｆｅ３＋等顺磁性金属螯合物，研究了Ｇｄ３＋，Ｍｎ２＋和Ｆｅ３＋螯合物作为磁共振成像造影剂的主要性能。结果表明，ＧｄＤＴＰＡＢＴｒｉｓ，ＭｎＥＤＴＡＢＴｒｉｓ和ＦｅＥＤＴＡＢＴｒｉｓ在体外水溶液中对水质子的纵向弛豫率Ｒ１分别为５４，３．１和１．９Ｌ·ｍｍｏｌ－１·ｓ－１，均高于其相应母体螯合物在相同条件下的弛豫率。此外，这些螯合物还具有医用磁共振成像造影剂所要求的高水溶性和化学稳定性。     

2—（6—硝基—2—苯并噻唑偶氮）—5—二甲氨基苯甲酸与铜显色反应的研…

本研究了２－（６－硝基－２－苯并噻唑偶氮）－５－二甲氨基苯甲酸（６－ＮＯ２－ＢＴＡＭＢ）与铜的显色反应。结果表明，在ｐＨ２．０￣４．５的乙醇水溶液中６－ＮＯ２－ＢＴＡＭＢ与铜形成一种稳定的蓝绿色络合物，其最大吸收波长位于６５０ｎｍ处，表观摩尔吸收系数为７．７５×１０＾４Ｌ·ｍｏｌ＾－１·ｃｍ＾－１，络合物的组成为６－ＮＯ２－ＢＴＡＭＢ∶Ｃｕ＝１∶１，铜浓度在０￣１０μｇ／１０ｍｌ范围内服从比尔定     

A NOVEL REACTION BETWEEN Ge－Ge AND Fe－Fe BONDS IN COMPLEX （Me_2GeGeMe_2）［（η~5－C_5H_4）Fe（CO）］_2（μ－CO）_2 AND CRYSTAL STRUCTURE OF THE PRODUCT

ＡＮＯＶＥＬＲＥＡＣＴＩＯＮＢＥＴＷＥＥＮＧｅ－ＧｅＡＮＤＦｅ－ＦｅＢＯＮＤＳＩＮＣＯＭＰＬＥＸ（Ｍｅ_２ＧｅＧｅＭｅ_２）［（η~５－Ｃ_５Ｈ_４）Ｆｅ（ＣＯ）］_２（μ－ＣＯ）_２ＡＮＤＣＲＹＳＴＡＬＳＴＲＵＣＴＵＲＥＯＦＴＨＥＰＲＯＤＵＣＴ￥ＸｉｕＴ?..     

四甲基二硅桥连双(四甲基环戊二烯基)四羰基二铁的反应性

标题化合物1与HgCl~2反应, 除生成希望的产物2外, 还分离到2的歧化产物3和4。1经Na-Hg还原, 生成Fe-Fe键断裂的双铁负离子5, 5分别与多种氯化物反应, 生成在铁原子上引入取代基的衍生物6, 7和8。以元素分析、IR及^1H NMR谱表征了化合物2-4及6-8的分子结构。     

Chemical functionality of poly(methylenephosphine): phosphine-borane adducts and methylphosphonium ionomers

The chemical functionality of poly(methylenephosphine) n-Bu[MesP-CPh(2)](n)H () is examined in reactions with two isoelectronic species, namely BH(3) and CH(3)(+). The potential reactivity of polymer is modelled by examining the reactivity of molecular phosphines bearing similar substituents as the polymer. In particular, the phosphine-borane adducts Mes(Me)P(BH(3))-CPh(2)H () and Mes(Me)P(BH(3))-CPh(2)SiMe(2)H () are prepared from the reaction of BH(3).SMe(2) with Mes(Me)P-CPh(2)H () or Mes(Me)P-CPh(2)SiMe(2)H (), respectively. Treating with MeOTf affords the methylated model compound, [Mes(Me)(2)P-CPh(2)H]OTf (). X-Ray crystal structures are reported for each model compound. The reaction of n-Bu[MesP-CPh(2)](n)H (M(n) = 3.89 x 10(4), PDI = 1.34) with BH(3).SMe(2) affords the phosphine-borane polymer n-Bu[MesP(BH(3))-CPh(2)](n)H () (M(n) = 4.13 x 10(4), PDI = 1.26). In contrast, methylation of phosphine polymer gives n-Bu[MesP-CPh(2)](x)-/-[MesP(Me)-CPh(2)](y)H.(OTf)(y) () where approximately 50% of the phosphine moieties are methylated (from (31)P NMR).     

Nickel and iron complexes with N,P,N-type ligands: synthesis, structure and catalytic oligomerization of ethylene

The N,P,N-type ligands bis(2-picolyl)phenylphosphine (), bis(4,5-dihydro-2-oxazolylmethyl)phenylphosphine (), bis(4,4-dimethyl-2-oxazolylmethyl)phenylphosphine () and bis(2-picolyloxy)phenylphosphine () were used to synthesize the corresponding pentacoordinated Ni(ii) complexes [Ni{bis(2-picolyl)phenylphosphine}Cl(2)] (), [Ni{bis(4,5-dihydro-2-oxazolylmethyl)phenylphosphine}Cl(2)] (), [Ni{bis(4,4-dimethyl-2-oxazolylmethyl)phenylphosphine}Cl(2)] () and [Ni{bis(2-picolyloxy)phenylphosphine}Cl(2)] (), respectively. The hexacoordinated iron complexes [Fe{bis(2-picolyl)phenylphosphine}(2)][Cl(3)FeOFeCl(3)] (), [Fe{bis(4,5-dihydro-2-oxazolylmethyl)phenylphosphine}(2)][Cl(3)FeOFeCl(3)] () and the tetracoordinated complex [Fe{bis(4,4-dimethyl-2-oxazolylmethyl)phenylphosphine}Cl(2)] (abbreviated [FeCl(2)(NPN(Me2)-N,N)]) were prepared by reaction of FeCl(2).4H(2)O with ligands , respectively. The crystal structures of the octahedral complexes and , determined by X-ray diffraction, showed that two tridentate ligands are facially coordinated to the metal centre with a cis-arrangement of the P atoms and the dianion (mu-oxo)bis[trichloroferrate(iii)] compensates the doubly positive charge of the complex. The cyclic voltammograms of and showed two reversible redox couples attributed to the reduction of the dianion (Fe(2)OCl(6))(2-) (-0.24 V for and -0.20 V for vs. SCE) and to the oxidation of the Fe(ii) ion of the complex (0.67 V for and 0.52 V for vs. SCE). The cyclic voltammogram of [FeCl(2)(NPN(Me2)-N,N)] showed a reversible redox couple at -0.17 V vs. SCE assigned to the oxidation of the Fe(ii) atom and an irreversible process at 0.65 V. The complexes , and [FeCl(2)(NPN(Me2)-N,N)] have been evaluated in the catalytic oligomerization of ethylene with AlEtCl(2) or MAO as cocatalyst. The nickel complex proved to be the most active precatalyst in the series, with a turnover frequency (TOF) of 61 800 mol(C(2)H(4)) mol(Ni)(-1) h(-1) with 10 equiv. of AlEtCl(2) and 12 200 mol(C(2)H(4)) mol(Ni)(-1) h(-1) with 200 equiv. of MAO. Precatalysts and were the most selective in butenes, up to 90% with 6 equiv. of AlEtCl(2) and 89% with 2 equiv. of AlEtCl(2), respectively, and up to 92% butenes with 400 equiv. of MAO and 91% butenes with 200 equiv. MAO, respectively. The best selectivities for 1-butene were provided by and AlEtCl(2) (up to 31% with 6 equiv.) and with MAO (up to 72% with 200 equiv.). The iron complexes were not significantly active with AlEtCl(2) or MAO as cocatalyst.     

Haloacetylated enol ethers: 18 : Synthesis of alkyl 6-[azol-3(5)-yl]hexanoates

A convenient method for the synthesis of eight alkyl 6-[4,5-dihydroisoxazol-3-yl(-pyrazol-3(5)-yl)]hexanoates from the cyclocondensation of methyl 10,10,10-trifluoro[chloro]-9-oxo-7-methoxydec-7-enoates and hydroxylamine hydrochloride or hydrazine hydrochloride, respectively, in ethanol as solvent is reported. The reaction of methyl 10,10,10-trichloro-9-oxo-7-methoxydec-7-enoates with hydrazines furnished the pyrazole derivatives with the simultaneous transformation of trichloromethyl to carboxyl group.     

Sterically variable dizinc complexes bearing bis(iminopyridyl)phenolate ligands: synthesis, structures and reactivity studies

A series of chiral dizinc complexes of the type [(2,6-{ArN=C(Me)C5H3N}2C6H3O)Zn2(micro-Cl)Cl2] [Ar=2,6-i-Pr2C6H3 (), 2,6-Me2C6H3 (), 2,4,6-Me3-C6H2 (), 2,4-Me2C6H3 ()] can be conveniently prepared in good yield by the template reaction of 2,6-{O=C(Me)C5H3N}2C6H3OH with an excess of the corresponding aniline and two equivalents of zinc dichloride in n-BuOH at elevated temperature. Alternatively, the pro-ligands, 2,6-{(ArN=C(Me)C5H3N}2C6H3OH [Ar=2,6-i-Pr2C6H3 (L1-H), 2,6-Me2C6H3 (L2-H), 2,4,6-Me3C6H2 (L3-H), 2,4-Me2C6H3 (L4-H)], can be isolated and then treated with two equivalents of zinc dichloride to afford . Interaction of with two equivalents of NaOAc in the presence of TlBF4 gives the diacetate-bridged salt [(L1)Zn2(micro-OAc)2](BF4) () while with Nadbm (dbm=dibenzoylmethanato) the bis(dbm)-chelated salt [(L1)Zn2(dbm)2](BF4) () is obtained. Hydrolysis occurs on reaction of with TlOEt to furnish [(L1)Zn2(micro-OH)Cl2] () as the only isolable product. Conversely, reaction of with Tlhp (hp=2-pyridonate) affords the neutral bis(pyridonate)-bridged trimetallic complex [(L1)Zn3(micro-hp)2Cl3] () as the major product along with as the minor one. Complex and mixtures of / act as modest activators for the ring-opening polymerisation of epsilon-caprolactone. Single crystal X-ray diffraction studies have been performed on , , , , and reveal Zn...Zn separations in the range: 3.069(4)-4.649(6) A.     

紫尿酸–Fe(Ⅲ)分光光度法测定盐酸羟胺

在碱性介质及溴化十六烷基吡啶存在条件下,盐酸羟胺与Fe(Ⅲ)–紫尿酸体系发生显色反应形成离子缔合物,该离子缔合物在635 nm波长处有一个吸收峰,其表观摩尔吸光系数ε=2.05×104 L/(mol·cm),据此建立了测定盐酸羟胺的间接分光光度法。盐酸羟胺的质量浓度在0~2.4 mg/L范围内与吸光度与呈良好的线性,线性相关系数r=0.999 8,方法的检出限为0.01 mg/L。将该方法用于盐酸羟胺的测定,其测定结果与国标法测定结果相吻合,加标回收率为95.0%~104.0%,测定结果的相对标准偏差为0.51%~1.29%(n=5)。该方法灵敏度高,操作简便,可用于盐酸羟胺含量测定。     

Some reactions of 4-[(2′,3′-diphenyl-6′-methoxy-5′-benzofuranyl)-methylene]- and 4-[(2′,3′-diphenyl-5′-methoxy-6′-benzofuranyl)-methylene]-2-phenyloxazolin-5-one

2,3-Diphenyl-5-formyl-6-methoxybenzofuran was reacted with hippuric acid to give 4-[(2′,3′-diphenyl-6′-methoxy-5′-benzofuranyl)methylene]-2-phenyloxazolin-5-one. The above mentioned oxazolone yielded 2,3-diphenyl-6-methoxybenzofuranylacetic acid by reaction with hydrazine hydrate, nitrous acid, benzene followed by acid hydrolysis. The reactions of the oxazolone with hydroxylamine hydrochloride and primary or secondary amines were also investigated.     

Mono- and dinuclear cobalt complexes with chelating or bridging bidentate P,N phosphino- and phosphinito-oxazoline ligands: synthesis, structures and catalytic ethylene oligomerisation

Cobalt(ii) complexes of the type [CoCl(2)(P,N)], where P,N represents a heterobidentate phosphino- or phosphinito-oxazoline-type ligand, have been synthesised and characterised by infrared spectroscopy and elemental analysis. Their molecular structures were established by single-crystal X-ray diffraction in the solid state. Whereas the phosphino-oxazoline complex [CoCl(2){Ph(2)PCH(2)ox(Me2)}] (Ph(2)PCH(2)ox(Me2) = 2-[(diphenylphosphanyl)-methyl]-4,4-dimethyl-4,5-dihydro-oxazole) () and the phosphinito-oxazoline complexes [CoCl(2){Ph(2)POCH(2)ox(Me2)}] (Ph(2)POCH(2)ox(Me2) = 1-[4,4-dimethyl-2{1-oxy(diphenylphosphino)-1-methyl}]-4,5-dihydro-oxazole) () and [CoCl(2){Ph(2)POCMe(2)ox(Me2)}] (Ph(2)POCMe(2)ox(Me2) = 1-[4,4-dimethyl-2- [1-oxy(diphenylphosphino)-1-methylethyl]]-4,5-dihydrooxazole) () are mononuclear, the phosphino-oxazoline complexes [CoCl(2){micro-i-Pr(2)PCH(2)ox}](2) (i-Pr(2)PCH(2)ox = 2-[(diisopropyl-phosphanyl)-methyl]-4,5-dihydro-oxazole) () and [CoCl(2){micro-Ph(2)PCH(2)ox}](2) (Ph(2)PCH(2)ox = 2-[(diphenyl-phosphanyl)-methyl]-4,5-dihydro-oxazole) () are dinuclear compounds and contain two bridging phosphino-oxazoline ligands which form a 10-membered ring. In the course of this work, the zwitterionic complex [CoCl(3){Ph(2)PCH(2)C(O)OCH(2)CMe(2)NH(3)] () was obtained and characterised by X-ray diffraction in which the oxazoline ring has been opened. Air-oxidation of the phosphine function of the mononuclear P,N chelate complex yielded the blue N,O-bridged, centrosymmetric dinuclear complex [[upper bond 1 start]CoCl(2){micro-OPPh(2)CH(2)[lower bond 1 start]C[double bond, length as m-dash]N[upper bond 1 end]CMe(2)CH(2)O[lower bond 1 end]}](2) () which contains a 12-membered ring. All these complexes are paramagnetic and their magnetic moments in solution were measured by the Evans method. Complexes were evaluated in the catalytic oligomerisation of ethylene with AlEtCl(2) or methylaluminoxane (MAO) as cocatalysts and provided moderate activities. In the presence of AlEtCl(2) (6-14 equiv.), the selectivities for ethylene dimers were higher than 92% and complex showed the highest turnover frequency with 14 equiv. of AlEtCl(2). When MAO was used as cocatalyst, the catalytic activities were similar to those with AlEtCl(2) but significant amounts of C(6)-C(12) oligomers were produced.     

Haloacetylated enol ethers. 7 . Synthesis of 3-aryl-5-trihalomethylisoxazoles and 3-aryl-5-hydroxy-5-trihalomethyl-4,5-dihydroisoxazoles

β-Aryl-β-methoxyvinyl trihalomethyl ketones 1a-g, 2a-g [aryl = p-YC₆H₄ where Y= H, Me, OMe, F, Cl, Br, NO₂] are cyclocondensed with hydroxylamine hydrochloride to afford the 3-aryl-5-hydroxy-5-trihalomethyl-4,5-dihydroisoxazoles 3a-g, 4a-f in good yield. The dehydratation of compounds 3a-g with concentrated sulfuric acid, led the corresponding 3-aryl-5-trichloromethylisoxazoles 5a-g . An alternative one-pot procedure yields 3-aryl-5-trihalomethylisoxazoles 5,6a-g directly by cyclocondesation of 1,2a-g with hydroxylamine hydrochloride in the presence of an excess of concentrated hydrochloric acid.     

Critical assessment of two classical synthetic methods for preparation of thiophene-substituted isoxazoles

Formation of thiophene-substituted isoxazoles by reaction of chalcone dibromides and 1,3-diketones with hydroxylamine hydrochloride has been examined under different conditions. Use of KOH as base in the reaction of dibromide chalcone analogs with hydroxylamine hydrochloride yields mixtures of isomeric isoxazoles in modest yields. Replacement of KOH with pyridine affords negligible amounts of isoxazoles only, the intermediate 2-bromoprop-2-en-1-one being isolated from the reaction as the major product. Substitution of the β-bromine atom from a chalcone dibromides with a methoxy group by solvolysis occurred when no base was used. Mixtures of isomeric isoxazoles in which the isoxazole that had a 2-thienyl group at position 5 were always major components, were obtained in good yields from reaction of thiophene-containing 1,3-diketones with hydroxylamine hydrochloride, irrespective of reaction pH. At low pH, regioselectivity was poorer than that observed for reaction of chalcone dibromides with hydroxylamine hydrochloride, but yields were substantially better. At high pH, yields were comparable with those at low pH and regioselectivity for 3-aryl-5-(2-thiophenyl)isoxazole was slightly enhanced, but the dioxime corresponding to the initial 1,3-diketone was also produced in low yields as a mixture of stereoisomers.