A Novel Acetyl Migration

Acetylmigrationhasbeenfoundinsteroids,glyceridesandcarbohydrateschemistry.Herewereportanovelacetylndgrationbetweentwophenolicgroupsinonenaphthalenetriol.InourattemptstowardtheasynuhetricsynthesisofopticallypureR-( )-shikonin1whichshowsabroadspectrumofsignificantbiologicalactivitiesincludingantiinflanimatory',antibacterialandantifungal',inununostimulating',anticancer4,aswelIasstronginhibitionoftopoisomeraseI',conunpound2wasthekeyintermediate.Accordingtooursyntheticroute(Scheme1),oxidationofl,…     

Fluorescence lifetimes of benzyl and deuterium-substituted benzyl radicals

Fluorescence lifetimes of C₆H₅CH₂, o-, m-, p-DC₆H₅CH₂, C₆H₅CD₂, C₆D₅CH₂, and C₆D₅CD₂ have been measured at 77 K in rigid glasses. Very long decay times are observed for all the radicals. There is a dramatic deuterium effect upon ring deuteration; alkyl deuteration lengthens the lifetime if the phenyl ring is already deuterated, but otherwise exhibits a slight inverse deuterium effect. The oscillator strength of the ²A₂ ? ²B₂ transition is calculated to be no larger than 8 × 10^?4.     

Acetyl Derivatives of 3-Quinuclidone

Methods have been developed for the synthesis of mono- and bisacetyl derivatives of 2-hydroxyarylmethylene-3-quinuclidone oximes.     

Radical polymerization of methyl acrylate by use of benzyl N,N-diethyldithiocarbamate in combination with tetraethylthiuram disulfide as a two-component iniferter

Polymerization of methyl acrylate (MA) with benzyl N, N-diethyldithiocarbamate (BDC) was carried out in bulk or in benzene under UV irradiation. The polymerization proceeded to give a high yield of polymer, however it was found that BDC did not function as an iniferter in the MA polymerization. Bimolecular termination leading to deactivation of the iniferter site was observed during the polymerization in preference to chain transfer and primary radical termination which reproduce the iniferter site. The deactivation was successfully prevented by combining BDC and tetraethylthiuram disulfide (TD) as a two-component iniferter. This two-component iniferter system was also applied to synthesis of a star polymer with 1,2,4,5-tetrakis (N,N-diethyldithocarbamylmethyl) benzene (DDC) as a tetrafunctional photoiniferter. © 1994 John Wiley & Sons, Inc.     

五羰基乙酰基锰的深度氢硅烷化

采用两步法合成(CO)₅MnCOCH₃ (1), 然后对1与Me₂PhSiH的深度氢硅烷化反应做9 h的¹H NMR连续监控, 通过将反应物和衍生物的特征峰与内标物C₆H₅(CH₂)₂C₆H₅的特征峰对照直接积分定量, 得到适时含量(mmol)随反应时间改变(h)的变化规律。期间共得到了9种中间体或最终产物, 通过核磁波谱对比, 确定了这些化合物的分子结构。除了对其中6种化合物的特征峰积分直接定量外, 对另外3个化合物采用化学计量结合特征峰积分间接定量, 并对其反应机理做出了合理的解释。最后提出了深度氢硅烷化的多步反应与双通道机理, 并且对反应原料1和Me₂PhSiH中Mn和Si进行了全程跟踪, 结果发现, 在9 h时, Mn总含量高达90.7%, 而Si总含量高达91.4%。     

新型Zhuo酚酮类糖苷化合物的合成

根据Zhuo酮的结构特点，对Zhuo酚酮类化合物与半乳糖的Kenigs-Knorr反应进 行了研究。探索出一种具有较高立体选择性的合成方法，从而制得四种具有β－构 型的单一端基异构体的Zhuo酚酮半乳糖苷新化合物。生成的新化合物不但保持了原 有的生理活性，而且降低了毒性、提高了药效，为人工合成Zhuo酚酮类增添新化合 物的同时，也扩展了此类化合物的应用领域。应用元素分析、核磁共振、红外光谱 表征了它们的结构。     

Electronic spectra of paramethoxy benzyl alcohol and parachloro benzyl cyanide

The electronic absorption spectra of paramethoxy benzyl alcohol (pmba) and parachloro benzyl cyanide (pcbc) are described. The broad features of the spectra of the molecules are consistent with allowed transition forC _2v symmetry. However, the solid state and glass matrix spectra of pmba at 77K indicate possible deviation from planarity in the structure of the molecule. In pcbc, it is pointed out that intensity borrowing may be responsible for the large intensity of the vibrationally-induced part of the spectra, in which non-totally symmetric vibrations are excited.     

Acetyl ketene aminals in Nenitzescu reaction

Nenitzescu reaction of acetyl ketene aminals (N,N-acetals) was investigated. The interaction of 2-acetyl-1-amino-1-anilinoethene with benzoquinone gave 3-acetyl-2-amino-7a-hydroxy-1-phenyl-5,7a-dihydro-1H-indol-5-one, which was then transformed into 3-acetyl-2-amino-6-chloro-5-hydroxy-1-phenylindole. The reaction of benzoquinone with 2-acetyl-1-amino-1-benzoylaminoethene led to the corresponding hydroquinone-adduct which was oxidized to 4-acetylamino-5-(2,5-dihydroxyphenyl)-2-phenyloxazole. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 160–165, January, 1999.     

五羰基乙酰基锰的深度氢硅烷化

采用两步法合成(CO)₅MnCOCH₃ (1), 然后对1与Me₂PhSiH的深度氢硅烷化反应做9 h的¹H NMR连续监控, 通过将反应物和衍生物的特征峰与内标物C₆H₅(CH₂)₂C₆H₅的特征峰对照直接积分定量, 得到适时含量(mmol)随反应时间改变(h)的变化规律。期间共得到了9种中间体或最终产物, 通过核磁波谱对比, 确定了这些化合物的分子结构。除了对其中6种化合物的特征峰积分直接定量外, 对另外3个化合物采用化学计量结合特征峰积分间接定量, 并对其反应机理做出了合理的解释。最后提出了深度氢硅烷化的多步反应与双通道机理, 并且对反应原料1和Me₂PhSiH中Mn和Si进行了全程跟踪, 结果发现, 在9 h时, Mn总含量高达90.7%, 而Si总含量高达91.4%。     

"一锅法"合成N-乙基咔唑乙酰化衍生物

以N-乙基咔唑为原料,通过“一锅法”合成了未见文献报道的单乙酰化衍生物3-乙酰基-9-乙基咔唑和双乙酰化衍生物3,6-二乙酰基-9-乙基咔唑,其结构经1H NMR,IR,MS和元素分析表征。     

Beyond benzyl grignards: facile generation of benzyl carbanions from styrenes

Benzylic functionalization is a convenient approach towards the conversion of readily available aromatic hydrocarbon feedstocks into more useful molecules. However, the formation of carbanionic benzyl species from benzyl halides or similar precursors is far from trivial. An alternative approach is the direct reaction of a styrene with a suitable coupling partner, but these reactions often involve the use of precious-metal transition-metal catalysts. Herein, we report the facile and convenient generation of reactive benzyl anionic species from styrenes. A Cu(I)-catalyzed Markovnikov hydroboration of the styrenic double bond by using a bulky pinacol borane source is followed by treatment with KOtBu to facilitate a sterically induced cleavage of the C-B bond to produce a benzylic carbanion. Quenching this intermediate with a variety of electrophiles, including CO(2), CS(2), isocyanates, and isothiocyanates, promotes C-C bond formation at the benzylic carbon atom. The utility of this methodology was demonstrated in a three-step, two-pot synthesis of the nonsteroidal anti-inflammatory drug (±)-flurbiprofen.     

Acetyl Exchange between Pyridine N-Oxides in Acetonitrile Solutions: An Attempt to Apply the Marcus Equation to Acetyl Transfer

Forty-three (including eight identical) reactions of acetyl transfer from N-acetyloxypyridinium salts to pyridine N-oxides in acetonitrile solutions were studied. The rate constants k ₂ vary in the range 10⁷-10^{- 1} l mol^{- 1} s^{- 1}; the equilibrium constants K, in the range 10⁷-10^{- 7}; the activation enthalpy H , in the range 17-30 kJ mol^{- 1}; the activation entropy -S , in the range 60-85 J mol^{- 1} K^{- 1}; and the heat of reaction -H ⁰, within ±50 kJ mol^{- 1}. All reactions occur in a single stage by the concerted SN2 mechanism with a low degree of bond cleavage in the transition state. The rate and equilibrium of the acetyl exchange are satisfactorily described by the Brönsted equation. The quality of predicting the reactivity is substantially improved by introducing into the correlation equation a second parameter, the rates of identical reactions.     

Relative rates of nucleophilic reactions of benzyl carbocation formed in photolysis of benzyl chloride and benzyl acetate in aqueous solution

Benzyl chloride and benzyl acetate were photolyzed in 30% methanol–water mixtures (V/V) at 0°C. The photolysis produces benzyl carbocations that react with nucleophiles. The reaction products were analyzed by gas chromatography or liquid chromatography. From the amounts of products the relative values of rate constants of reactions of benzyl carbocation with nucleophiles N and water k(N)/k(H₂O) were calculated. Benzyl carbocation reacts with I^?, Br^?, Cl^?, and Ac^? ions with approximately diffusion-controlled rate. A value of 2.4 × 10⁷ dm³ mol^?1 s^?1 for the rate constant k(H₂O) and a lifetime of 0.7 ns were estimated for benzyl carbocation in the aqueous solution.     

Oxidation of benzyl alcohols, benzyl halides, and alkylbenzenes with oxone

Oxidation of benzyl alcohols, benzyl halides, and alkylbenzenes to their corresponding oxidation products has been shown to be accomplished directly with oxone. The methodology that involves mere stirring/heating of the reactants and oxone in acetonitrile/water (1:1, v/v) is simple and practical, but is limited to substrates that do not contain sensitive functionalities and heteroaromatic rings.     

Dicubyl disulfide

Dicubyl disulfide (1) has been prepared in six steps from commercially available dimethyl-1,4-cubanedicarboxylate in 47% overall yield. In the final step, the previously unknown cubanethiol 2 was oxidized to disulfide 1. X-ray crystallography for 1 reveals the shortest tetragonal C-S bond on record (1.771 A). In contrast to previous generalizations, density functional theory calculations predict a low S-S rotation barrier similar to that for t-BuSSBu-t. Low-temperature (13)C NMR (600 MHz) confirms the prediction.     

含卓酚酮基团的四乙酰基半乳糖苷的合成

环庚三烯酚酮;含卓酚酮基团的四乙酰基半乳糖苷的合成;Koenigs-Knorr糖基化反应