Selective monotetrahydropyranylation of symmetrical diols using P2O5/SiO2 under solvent-free conditions and their depyranylation

Selective protection of one of the hydroxyl group in 1, n-symmetrical diols is achieved by P2O5/SiO2-catalyzed reaction of the diol with dihydropyran under solvent-free conditions at room temperature. This selective protection is simple and it occurred under economically cheap conditions in high yield. The deprotected diol is simply obtained by refluxing of this compound in methanol using the same catalyst without any byproduct formation or additional purifications.     

Microwave-mediated selective monotetrahydropyranylation of symmetrical diols catalyzed by iodine

Selective protection of one hydroxyl group as its tetrahydropyranyl ether in 1,n-symmetrical diol is achieved by iodine-catalyzed reaction of the diol with dihydropyranyl ether under microwave irradiation.     

分光光度法测定钯的新显色剂 2-四唑偶氮-5-二乙氨基酚

研究了新显色剂2_四唑偶氮_5_二乙氨基酚 (TTZAPN)分光光度法测定Pd2 的条件。在 pH5.0的HAc -NaAc介质中 ,该试剂与Pd2 形成稳定的摩尔比为2∶1的紫红色络合物。其最大吸收波长在530nm处 ,表观摩尔吸光系数为4.51×104L·mol -1·cm -1 ,Pd2 质量浓度在0～1.0mg/L范围内遵守比尔定律。所拟方法直接测定钯 -碳催化剂和分子筛中微量钯 ,结果令人满意。     

Protection of the carbonyl groups in 1,2-indanedione: propellane versus acetal formation

The product resulting from the reaction between 1,2-indanedione and ethylene glycol under acidic catalysis is 2,5,7,10-tetraoxapropellane and not 1,2-dispirane as previously reported. Similar reactions also occur with 2-mercaptoethanol and 1,2-ethanedithiol, which form analogous propellanes and not corresponding thioacetals. This explains the difficulty of removing the protective groups under acidic conditions. These findings were corroborated by quantum chemical calculations. Under similar conditions, the longer-chain diol, 1,3-propyleneglycol and its thiol-analogue, 1,3-propanedithiol, form only mono-acetals, even when a 3-fold excess of the diol is applied. The nucleophilic attack, however, takes place at different positions: while propanedithiol forms the acetal at c-1, propylene glycol forms the acetal at c-2.     

A consecutive approach towards the stereoselective synthesis of trisubstituted THF domains

A highly efficient, consecutive approach for the construction of synthetically valued, enantiomerically pure, trisubstituted THF domains 3–10 in a stereoselective manner starting from glycal derived allylic alcohols 1a–1d under Sharpless asymmetric epoxidation (SAE) conditions is reported. The reaction involves the intramolecular asymmetric ring opening (ARO) of in situ formed enantiopure 2,3-epoxy alcohols followed by protection of the diol.     

TiO_2纳米管阵列的制备及其对316不锈钢光生阴极保护作用的研究

应用直接电化学阳极氧化法,于含氟电解液中,在纯钛表面制备一层整齐有序的TiO2纳米管阵列.扫描电子显微镜(SEM),X射线衍射(XRD)表征该纳米管阵列的形貌及晶体结构,光电化学联用系统研究其光电响应特性及对316L的光生阴极保护作用.结果表明:以TiO2纳米管阵列膜作为光生阳极时,在紫外光区(λ<387nm)有显著增强的光生电流响应,并对316不锈钢有较好的光生阴极保护作用.暗态下,光生电极电位仍可维持较长的一段时间,继续起到阴极保护作用.     

Asymmetric alkyldifluoroboranes and their use in secondary amine synthesis

[reaction: see text] Asymmetric diol boronic esters with potassium bifluoride form the corresponding alkyltrifluoroborate and free diol under mild conditions. Defluoridation with tetrachlorosilane produces an alkyldifluoroborane intermediate. This conversion of relatively unreactive boronic esters to derivatives that are strong Lewis acids opens new synthetic opportunities, as illustrated by the preparation of (R)-2-phenylpyrrolidine in 98% ee from a pinanediol or 1,2-dicyclohexyl-1,2-ethanediol boronic ester via potassium (2-phenyl-4-azidobutyl)trifluoroborate.     

Reactions at Only One of Two Equivalent Functional Groups

A common problem encountered by synthetic chemists is to carry out a reaction at just one of two similar functional groups in the substrate molecule. Examples include protection/deprotection of just one hydroxyl group in a diol, addition to only one carbonyl of a diketone, etc. The problem, as depicted below, is to find conditions which maximize formation of the monoproduct (XP) while minimizing the amounts of diproduct (P₂) and starting material (X₂).     

Total Synthesis of (−)-Lepadin F based on a Stereoselective Diels–Alder Reaction Controlled by a Ketolactone-type Dienophile

An efficient approach to the type III lepadin alkaloids (lepadins F and G) has been developed through a key Diels–Alder reaction, in which a novel ketolactone-type dienophile with chiral diol unit is employed to generate the desirable all-cis-trisubstituted cyclohexene with excellent regio- and stereoselectivity control. The subsequent selective sulfonylation of the diol unit followed by S_N2 cyclization under hydrogenation conditions could construct the substituted piperidine ring. By using this approach, (−)-lepadin F is synthesized from ethyl l -lactate for the first time.     

Wacker oxidation methodology for the synthesis of the benzo-fused acetal core of marticin

Methodology for the synthesis of the benzo-fused acetal core of marticin is described in this paper. Condensation of readily available 1-(2-allyl-3,6-dimethoxyphenyl)ethanone with diethyl oxalate under Claisen condensation conditions furnished (Z)-ethyl 4-(2-allyl-3,6-dimethoxyphenyl)-2-hydroxy-4-oxobut-2-enoate. Treatment of this with LiAlH₄ resulted in the formation of the diol, 1-(2-allyl-3,6-dimethoxyphenyl)-3,4-dihydroxybutan-1-one. Conversion of primary alcohol of the diol into the TBDMS ether followed by further reaction with LiAlH₄ and exposure to Wacker oxidation conditions resulted in the formation of (3,6-dimethoxy-9-methyl-10,13-dioxatricyclo[7.3.1.0^2,7]trideca-2,4,6-trien-11-yl)methanol, the core of marticin.     

超声辐射下醋酸钯催化Sonogashira偶联反应

超声辐射下无铜无胺无膦Pd(OAc)_2体系中进行Sonogashira偶联反应,建立了适用于碘代芳烃的Sonogashira芳基化反应的合成方法,此法具有反应条件温和、反应时间短、收率高的优点。     

Rapid Cleavage of Oligodeoxyribonucleotides from cis‐Diol‐Bearing Universal Polymer Support

Two sets of conditions have been proposed for the cleavage of oligodeoxyribonucleotides from cis‐diol‐bearing polymer supports and their complete deprotection. The first condition involves the use of spermine in the presence of Zn²⁺ ions in aqueous NH₃ at 60° for 1 h, while the second one employs the use of 0.5M LiOH in conjunction with 3.5M Et₃N/MeOH at 75° for 40–60 min, or under microwaves for 5–8 min, depending on the protection employed for nucleic bases.     

三氟甲基磺酸锌催化选择性合成2-苄基-4-氯苯酚

在温和条件下,Zn(OTf)2能有效催化氯化苄对对氯苯酚的C-苄基化反应,选择性合成杀菌剂2-苄基-4-氯苯酚（BCP）,合成的优化条件为n(对氯苯酚):n(氯化苄)=1.2:1,催化剂Zn(OTf)2对氯化苄摩尔分数为5%,60 ℃下反应6 h,用硝基甲烷为溶剂,氯化苄转化率和产物BCP的产率分别＞99%和94%。     

(Triisopropylsilyl)acetaldehyde acetal as a novel protective group for 1,2-diols

(Triisopropylsilyl)acetaldehyde dimethyl acetal (TIPS-ADMA) was synthesized from chlorotriisopropylsilane in three steps. Cyclic and acyclic 1,2-diols can be transformed to (triisopropylsilyl)ethylidene acetals (TIPS-AA). Removal of the acetal by LiBF₄ regenerates the starting diol in excellent yield even in the presence of an acetonide of 1,2-diol. The TIPS-AA group can survive under the deprotection conditions of the acetonide in acetic acid at 80 °C. Selective protection of 2,3- and 4,6-diols for O-methyl d-mannoside with TIPS-ADMA and selective deprotection of the acetals have been achieved.     

Carbonylation of functionalized diamine diols to cyclic ureas: application to derivatives of DMP 450

Synthesis of the cyclic urea core structure of the HIV protease inhibitor DMP 450 has been achieved via W(CO)₆/I₂-catalyzed carbonylation of diamine intermediates. Carbonylations of related functionalized diamines to derivatives of the DMP 450 core structure were also examined. Selected diamine diol substrates could be converted to the cyclic urea core structure by catalytic carbonylation without protection of the diol functionality.     

The action of bentonitic earth on natural product epoxides

The ring opening of the epoxide group in the epoxiguaianolides by commercially available bentonitic earth produces specifically the trans diol in good yield under mild conditions.     

Theoretical investigations of 1,4‐butanediol and 2‐butene‐1,4‐diol cyclodehydration using postprocessing visualization of quantum chemical calculation data

Cyclodehydration of 1,4‐butanediol and 2‐butene‐1,4‐diol to the corresponding cyclic ethers was studied using the AM1 semiempirical method. It was established that the cyclodehydration reaction of 1,4‐butenediol and 2‐butene‐1,4‐diol is effected by converting of semicyclic conformers in the presence of acidic and basic active centers. The calculation results indicate that a concerted mechanism is probably realized in the cyclodehydration of both diols, while the sequences of the predicted steps in the cyclodehydration reaction for 1,4‐butanediol and 2‐butene‐1,4‐diol are different. The calculated reaction heats for 1,4‐butanediol and 2‐butene‐1,4‐diol transformations are ?184.029 and ?308.746 kcal/mol, respectively. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

MgCl_2负载(dbm)_2Ti(OPh)_2催化乙烯聚合

烯烃聚合的新型非茂催化剂由于合成相对简便并具有一些新特点,近年来开始受到人们的关注[1,2].ＩＶＢ族金属的β二酮络合物与烷基铝或烷氧基铝形成的催化体系对烯烃聚合也显现出一定的聚合活性.在一定压力下,β二酮锆/ＭＡＯ均相催化乙烯聚合时具有较高聚合活性[3].β二酮钛催化剂对于丙烯无规聚合和苯乙烯间规聚合均有较好结果[4～6].本文将报道用ＭｇＣｌ2负载的二苯氧基二(二苯甲酰甲烷)钛络合物((ｄｂｍ)2Ｔｉ(ＯＰｈ)2),以甲基铝氧烷(ＭＡＯ)为助催化剂,常压催化乙烯聚合的结果.1　原料ＭｇＣｌ2为抚顺301厂产品.ＭＡＯ(1.4ｍｏｌ/Ｌ甲…     

包埋Ru(bpy)3Cl2的非线性光催化薄膜的制备和表征

采用溶胶－凝胶法在正硅酸乙酯水解的溶液中加入Ru(bpy)3Cl2,在非常温和 的条件下制备出具有多孔结构的薄膜,并利用FTIR,AFM,N2吸附等测试手段对其 进行了表征,验证了Ru(bpy)3Cl2在Belousov-Zhabotinsky反应中的光催化活性。 结果表明Ru(bpy)3Cl2被包埋在多孔结构中,使薄膜在BZ反应中具有了光催化性能 。     

Improved Synthesis of Tricyclo (5.2.1.04,10) Decane-2,5,8-Trione by a Pauson-Khand Intramolecular Bis-Annulation

The title compound 1 has been synthesized from diol 3a, either directly or after protection of the two hydroxy groups as benzyl ethers, by an intramolecular Pauson-Khand bis-annulation, followed by catalytic hydrogenation and oxidation in overall yields ranging from 15% (free diol) to 35% (dibenzyl ethers).