催化量的氧化钙-硅胶对Sharpless烯丙醇不对称环氧化的影响

当在Sharpless试剂中加入催化量的金属氢化物和硅胶后, 烯丙醇的不对称环氧化反应时间大为缩短, 而化学和光学产率不受影响。着重讨论了氢化钙和硅胶对Sharpless烯丙醇不对称环氧化的作用。     

催化量的氢化钙-硅胶对Sharpless烯丙醇不对称环氧化的影响

1980年,Sharpless发现用他的试剂[Ti-(OiPr)_4,(+)-或(-)-酒石酸和叔丁基过氧化氢]可对烯丙醇进行不对称环氧化。以后该反应广泛地应用于许多光学活性天然产物的     

烯丙醇不对称环氧化新方法

一个新的金属催化的烯丙醇不对称环氧化(asymmetric epoxidation A.E)似比以前所有烯丙醇不对称环氧化方法为好。这个比较简单的新方法引人注意的一个方面是对映选择性非常之高而且所需试剂(+)-或(-)-酒石酸二酯,四异丙氧钛和叔丁基过氧化氢都容易得到。自从 1980年 Sharpless等发现这个方法以     

钼、钨系过氧化物在Sharpless烯烃环氧化反应中的应用*

钼、钨系过氧化物是非常重要的Sharpless烯烃环氧化催化剂,有着非常广泛的工业发展前景。本文综述了钼、钨系过氧化物的种类,结构,合成方法及催化活性,分析了各种钼、钨系过氧化物的特点以及在催化环氧化领域的发展现状。同时,本文还讨论了钼、钨系过氧化物催化烯烃环氧化反应的机理。评述了在催化环氧化领域中两种主要理论——Mimoun机理与Sharpless机理的争论焦点及发展现状,以及计算化学对两种理论中间过渡态的研究进展,并且重点分析了Sharpless机理的过渡态结构。此外,本文还综述了影响钼、钨系过氧化物催化剂反应活性的各种因素以及质子所产生的副反应。最后,本文对应用于催化环氧化领域的钼、钨系过氧化物未来的研究方向提出了建议。     

Ti(OR)4类化合物与一些醇及其衍生物交换反应的规律

我们在探讨Sharpless不对称环氧化反应机理,提高水溶性环氧醇产率,以及改进杂氮钛三环化合物合成方法的工作中,遇到了Ti(OR)_4类化合物与一些醇及其衍生物的配体交换反应。找出这类反应的规律,将有助手以上问题的研究。     

Sharpless试剂的改良及应用

本文总结了最近改良 Sharpless 烯丙醇不对称环氧化试剂[Ti(OiPr)_4,酒石酸酯]的几种方法,通过在试剂中加入几种催化剂,改变试剂组成或相对含量,优化了反应条件,扩大了试剂的使用范围。     

可溶性钼催化的氧转移反应I.1,5-顺，顺-环辛二烯分步环氧化反应的动力学研究

研究了以可溶住钼为催化剂,叔丁基过氧化氢环氧化1,5-顺,顺-环辛二烯的反应动力学。主要产物为单环氧和双环氧化合物,按照一组动力学公式使用计算机模拟分析处理了实验数据,得出环氧化反应是分步进行的,首先产生单环氧产物然后进行第二步环氧化。从40—90℃温度范围内的速度常数求出两步反应的活化焓基本相同,使第二步反应明显减慢的原因在于两步的活化熵上的差别,这可归结于由于环氧基团的导人引起空间阻碍致使六价钼络合物难于与烯烃进一步配位。这是因为双烯是取顺,顺构型,从而使两个双键之间的空间更为拥挤,用体积较大的氧化剂过氧化羟基异丙苯溶液代替叔丁基过氧化氢不能得到双环氧产物也证实了这个推论。     

血癌调节剂—（4S,5R）—5—羟基—4—癸内酯的合成

(4S,5R)-5-羟基-4-癸内酯1对血癌具有调节作用。本文首先利用Sharpless动力学拆分反应制得光学活性的环氧化合物,然后再通过其它反应合成具有生理活性的化合物1。     

槐尺蠖性信息素的不对称合成

本文以丙炔醇和正溴庚烷为起始原料经过炔烃偶联,格氏试剂偶联反应,用Sharpless不对称环氧化反应合成了槐尺蠖性信息素cis-3,4-环氧-(Z,Z)-6,9-十七碳二烯的两个光学异构体.     

ICP—AES法测定钢铁及高温合金中痕量硒

测定钢铁及合金中较高含量的硒.国家(?)(?)(?)(?)采用品酸胫胺-碘量法.而对于钢中原量硒的测定.国 家(?)(?)尚(?)建立方法,(?)(?)业标准大都采用(?)剂(?)取吸光光度法如:(?)氨基联苯胺-甲苯萃取吸光(?)(?)(?)或2.3(?)氨基萘(?)氯甲烷萃取吸光光度法(?)(?)与采用氢化物分离原子吸收光谱法(?)测定我们根据硒在盐酸(?)夜中容易被还原剂还原为(?)素状态析出的特性.配以适当的吸附剂吸附元素硒,息(?)使具与基体元素分离.然后(?)ICP AES法进行测定(?)(?)法已经参与(?)(?)国家级高温合金(?)(?)标准(?)中(?)量硒的定值工作.所得数据与参(?)定值工作的各(?)数据的平均值吻合本方法最低检出限量为(?)(?)(?)     

Evidence for involvement of cationic intermediate in epoxidation of chiral allylic alcohols and unfunctionalised alkenes catalysed by MnIII(quinazolinone) complexes

A pair of Mn^III(quinazolinone) complexes was prepared and evaluated in the catalytic epoxidation of the chiral allylic alcohols and unfunctionalised alkenes with iodosylbenzene. Epoxidation of chiral allylic alcohols with 1,3-allylic strain proceeded chemo- and diastereoselectively to give threo-epoxy alcohol (up to 99% d.r). Epoxidation of unfunctionalised alkenes by the proposed catalyst system proceeded nonselectively, as evidenced by the formation of isomerization and rearrangement products in the epoxidation of (Z)-stilbene. A three-step pathway involving a cationic intermediate is proposed for the formation of isomerization and rearrangement products. The fact that only products resulting from the cationic intermediate were detected in the oxidation of a mechanistic probe, (2-methoxy-3-vinylcyclopropyl)benzene, with Mn^III(quinazolinone) and PhIO substantiated the cationic oxygen transfer mechanism.     

Highly enantio- and diastereoselective one-pot synthesis of acyclic epoxy alcohols with three contiguous stereocenters

Two highly enantio- and diastereoselective one-pot procedures for the synthesis of epoxy alcohols with up to three contiguous stereocenters are reported. Route one involves asymmetric addition of an alkylzinc reagent to an enal followed by diastereoselective epoxidation. Route two entails asymmetric vinylation of an aldehyde with divinylzinc reagents and subsequent diastereoselective epoxidation. The oxidant for the epoxidation is generated by exposure of the allylic alkoxide intermediate and the remaining organozinc reagent to dioxygen. Upon addition of catalytic titanium tetraisopropoxide, the directed epoxidation yields the epoxy alcohols with good to excellent yields.     

Catalytic asymmetric allylation of ketones and a tandem asymmetric allylation/diastereoselective epoxidation of cyclic enones

A simple procedure is reported for the catalytic asymmetric allylation of ketones, utilizing titanium tetraisopropoxide, BINOL, 2-propanol additive, and tetraallylstannane as allylating agent. A variety of ketone substrates, including acetophenone derivatives and alpha,beta-unsaturated cyclic enones, reacted to form tertiary homoallylic alcohols in good yields (67-99%) and with high levels of enantioselectivity (generally >80%). A novel one-pot enantioselective allylation/diastereoselective epoxidation has also been introduced. Thus, upon completion of the allyl addition to conjugated cyclic enones, 1 equiv of tert-butyl hydroperoxide is added and the directed epoxidation of the allylic double bond ensues to afford the epoxy alcohol with high diastereoselectivity.     

Highly selective, recyclable epoxidation of allylic alcohols with hydrogen peroxide in water catalyzed by dinuclear peroxotungstate

The highly chemo-, regio-, and diastereoselective and stereospecific epoxidation of various allylic alcohols with only one equivalent of hydrogen peroxide in water can be efficiently catalyzed by the dinuclear peroxotungstate, K2[[W(=O)(O2)2(H2O)]2(mu-O)].2H2O (I). The catalyst is easily recycled while maintaining its catalytic performance. The catalytic reaction mechanism including the exchange of the water ligand to form the tungsten-alcoholate species followed by the insertion of oxygen to the carbon-carbon double bond, and the regeneration of the dinuclear peroxotungstate with hydrogen peroxide is proposed. The reaction rate shows first-order dependence on the concentrations of allylic alcohol and dinuclear peroxotungstate and zero-order dependence on the concentration of hydrogen peroxide. These results, the kinetic data, the comparison of the catalytic rates with those for the stoichiometric reactions, and kinetic isotope effects indicate that the oxygen transfer from a dinuclear peroxotungstate to the double bond is the rate-limiting step for terminal allylic alcohols such as 2-propen-1-ol (1a).     

Asymmetric addition of alkylzinc reagents to cyclic alpha,beta-unsaturated ketones and a tandem enantioselective addition/diastereoselective epoxidation with dioxygen

Although over 100 catalysts have been reported to catalyze the asymmetric addition of alkyl groups to aldehydes, these catalysts fail to promote additions to ketones with >90% enantioselectivity. This paper describes the asymmetric 1,2-addition of alkyl groups to conjugated cyclic enones to give allylic alcohols with chiral quaternary centers. The resultant allylic alcohols are converted into epoxy alcohols with excellent diastereoselectivities. Treatment of the epoxy alcohols with BF3.OEt2 induces a semipinacol rearrangement to provide alpha,alpha-dialkyl-beta-hydroxy ketones with all-carbon chiral quaternary centers. We also report a one-pot procedure for the asymmetric addition/diastereoselective epoxidation reaction. Simply exposing the reaction mixture to dioxygen after the asymmetric addition reaction is complete results in epoxidation of the allylic alcohol with high diastereoselectivity.     

离子液体在不对称催化反应中的应用进展

综述了近年来离子液体在不对称催化反应中的应用,包括不对称Aldol反应、不对称氟化反应、酶催化的不对称还原反应、不对称催化氢化反应、不对称硅腈化反应、不对称环丙烷化反应、烯丙基的不对称取代反应、环氧化物的不对称开环反应、不对称环氧化反应、烯烃的不对称双羟基化反应、酶催化的醇的动力学拆分。参考文献43篇。     

Highly efficient catalytic asymmetric epoxidation of allylic alcohols by an oxovanadium-substituted polyoxometalate with a regenerative TADDOL-derived hydroperoxide

The oxovanadium(IV) sandwich-type POM catalyzes the chemo-, regio-, and stereoselective epoxidation of allylic alcohols by chiral hydroperoxides with very high catalytic efficiency (up to 42 000 TON), a potentially valuable oxidation for the development of sustainable processes. By using the sterically demanding, TADDOL-derived hydroperoxide TADOOH as the chiral oxygen source, enantiomeric ratios (er) of up to 95:5 have been achieved.     

Selective Aerobic Oxygenation of Tertiary Allylic Alcohols with Molecular Oxygen

Aerobic epoxidation of tertiary allylic alcohols remains a significant challenge. Reported here is an efficient and highly chemoselective copper‐catalyzed epoxidation and semipinacol rearrangement reaction of tertiary allylic alcohols with molecular oxygen. The solvent 1,4‐dioxane activates dioxygen, thereby precluding the addition of a sacrificial reductant.     

An investigation into oxo analogues of molybdenum olefin metathesis complexes as epoxidation catalysts for alkenes

The oxo-imido molybdenum complex 2a is an effective catalyst at low catalyst loadings (0.5 mol % or below) for the epoxidation of a range of alkenes with ^tBuOOH in PhMe at 90 °C. Reactions are complete in less than 4 h and the products are isolated in high yields. The catalytic system is chemoselective for the epoxidation of electron-rich alkenes and allylic alcohols.     

Catalytic asymmetric generation of (Z)-disubstituted allylic alcohols

A one-pot method for the direct preparation of enantioenriched (Z)-disubstituted allylic alcohols is introduced. Hydroboration of 1-halo-1-alkynes with dicyclohexylborane, reaction with t-BuLi, and transmetalation with dialkylzinc reagents generate (Z)-disubstituted vinylzinc intermediates. In situ reaction of these reagents with aldehydes in the presence of a catalyst derived from (-)-MIB generates (Z)-disubstituted allylic alcohols. It was found that the resulting allylic alcohols were racemic, most likely due to a rapid addition reaction promoted by LiX (X = Br and Cl). To suppress the LiX-promoted reaction, a series of inhibitors were screened. It was found that 20-30 mol % tetraethylethylenediamine inhibited LiCl without inhibiting the chiral zinc-based Lewis acid. In this fashion, (Z)-disubstituted allylic alcohols were obtained with up to 98% ee. The asymmetric (Z)-vinylation could be coupled with tandem diastereoselective epoxidation reactions to provide epoxy alcohols and allylic epoxy alcohols with up to three contiguous stereogenic centers, enabling the rapid construction of complex building blocks with high levels of enantio- and diastereoselectivity.