DiastereoselectiveandEnantioselectiveSynthesisof(1S,2S)-2-Ethyl-1-aminocyclopropaneCarboxylicAcid

During the last decade, 1-aminocyclopropanecarboxylic acid and its derivatives (ACCS) have attracted increasing attention of organic and bioorganic chemists due to their outstanding biological properties, ranging from antimicrobial, insecticidal, plant growth and fruit ripening controls, etc.1. Moreover, the three-membered carbocycle provides building blocks of unprecedented synthetic potential because it undergoes selective ring opening, ring enlargement or cycloaddition reactions2. The mo…     

影响Snyder方程1gk′=1gk_w—Sφ中S值的因素

反相高效液相色谱的溶质保留行为与色谱体系性质的关系已经有人做过探讨。Snyder指出在1相似文献   

环丁酮光化学反应中S1/T1/S0交叉点的重要作用

势能面间的交叉在光化学反应中起着重要的作用 ,是由激发态反应物到基态产物发生无辐射跃迁的机制 .在本文中 ,我们用 CASSCF和态平均 CASSCF方法分别对环丁酮光化学反应的势能剖面及 S1,T1和 S0三个势能面间交叉进行了研究 .结果发现 ,基态和三态产物的形成是通过 S1,T1和 S0三个势能面交叉于同一区域 (称为 S1/T1/S0交叉点 )这一有效途径完成的 .　　60年代末 ,实验 [1－ 9]发现环丁酮和其它烷基酮 ,如丙酮、环戊酮的光化学反应机理很不一致 .主要体现在 ,i)环丁酮 (n,π态 )的α解离发生在 S1态势能面上 ,而其它烷基酮 (n,π态 …     

Etude des premières bandes d'absorption S0→S1 et S0→S2 du 5-méthoxyindole

The experimental and theoretical results obtained for 5-methoxyindole (5MOI) indicate a large energetic difference between the S₀ → S₁ and S₀ → S₂ transitions indicating a charge distribution very different from that of indole. A weak shoulder on the long wavelength side of the S₀ → S₁ band is attributed to a nπ* transition associated with the methoxy substituent. This feature has previously been attributed to a hot band. The effect of solvent on the molecule and the results obtained by the quantitative quantum CNDO/2 and CNDO/M methods are discussed.     

Time-resolved photoelectron imaging of S2 → S1 internal conversion in benzene and toluene

Ultrafast internal conversion of benzene and toluene from the S(2) states was studied by time-resolved photoelectron imaging with a time resolution of 22 fs. Time-energy maps of the photoelectron intensity and the angular anisotropy were generated from a series of photoelectron images. The photoelectron kinetic energy distribution exhibits a rapid energy shift and intensity revival, which indicates nuclear motion on the S(2) adiabatic surface, while the ultrafast evolution of the angular anisotropy revealed a change in the electronic character of the S(2) adiabatic surface. From their decay profiles of the total photoelectron intensity, the time constants of 48 ± 4 and 62 ± 4 fs were determined for the population decay from the S(2) states in benzene and toluene, respectively.     

尿嘧啶和5-氯尿嘧啶1S0→1S2跃迁动态结构的共振拉曼光谱

采用含时量子波包理论的简单模型对5-氯尿嘧啶和尿嘧啶的共振拉曼光谱开展了强度分析拟合, 获得了1(π, π*)激发态的几何结构变化动态特征. 结果表明, 尿嘧啶1S0→1S2跃迁的动态结构特征因5-位氯原子取代而改变. 5-氯尿嘧啶的动态结构特征主要沿C5=C6伸缩振动+C6H12 弯曲振动和N3H9/N1H7弯曲振动+N1C6伸缩振动反应坐标展开, 而尿嘧啶的动态结构特征主要沿嘧啶环的伸缩振动+C5H11/C6H12/N1H7弯曲振动和C4=O10伸缩振动反应坐标展开. π和π*轨道中氯原子的pz电子参与嘧啶环的p-π共轭作用导致了在1(π, π*)激发态上5-氯尿嘧啶的振动重组能更多地配分给嘧啶环的弯曲振动模式和C5=C6伸缩振动模式. 尿嘧啶在甲醇中的激发态动态结构特征与在水中的基本一致, 但波包沿C5H11/C6H12/N1H7弯曲振动+N1C6伸缩振动(υ12)和环呼吸振动(υ17)反应坐标的运动明显增强.     

Crystal Structure of (1R,4R;1S,4S)2-Amino-3-Cyano-1,4-Diphenyl-2-Cyclopentene-1-ol

1INTRODUCTIONIntheearly1970'sthreegroupsofinvestigatorsL,~,'foundthatlow-valenttita-nium,preparedbythereactionofstrongreducingagentswithtitaniumtrichlorideortitaniumtetrachlorideintetrahydrofuran,canabstractoxygenfromketonesoraldehydes,leadingtotheforma-tionofolefins.Theinterestinthereactioninducedbylow--valenttitaniumreagentsisincreasingandalargenumberoffunctionalgroupscanbereduceds4-6).Recent-ly,wefoundthatthetitlecompoundisObtainedbycy-cllzatlonreactionof(3--oxo-1,3-diphenyl)propyl-pro…     

A Convenient Approach to the Enantiopure (1S,2S,4S,5S)-and (1R,2S,4R,5S)-2,5-Bis(phenylmethyl)-1,4-diazabicyclo[2.2.2]-octane

Introduction1,4 Diazabicyclo[2 .2 .2 ]octane (DABCO)wasre portedtocatalyzeorganicreactionsduetoitsstrongbasici ty .1,2 Severalchiraltrans 2 ,3 disubstitutedDABCOshavebeensynthesizedandappliedtotheasymmetricBaylis Hillmanreaction3andvicinalhydroxylation .4ThefirstsynthesisofthetitlecompoundwasreportedbySoai5from (2S ,5S) bis(phenylmethyl)piperazine (1) ,asshowninScheme 1.Butthisprocedureislengthy ,andtheoverallyieldisnotsosatisfactory .Besides ,thereport edmethodforthepreparationof 1is…     

One-pot Synthesis and Crystal Structure of （1S,2R,3S,4R,5S）-1-Phenyl-2,4-dibenzoyl-3,5-difurylhexanol

(1S,2R,3S,4R,5S)-1-Phenyl-2,4-dibenzoyl-3,5-difurylhexanol 1 was synthesized by one-pot reaction of hypnone and furfurol in alkali H2O/EtOH solution and structurally defined to contain a chair-formed aliphatic carbocycle, on which the bulky substituents occupy the equatorial positions.     

A Convenient Approach to the Enantiopure （1S, 2S, 4S, 5S ）- and（ 1R, 2S, 4R, 5 S ）-2,5-Bis （ phenylmethyl）-l, 4-diazabicyclo[ 2.2.2 ] -octane

Cyclodipepflde (3S, 6S )-bis (phenylmethyl) piperazlne-2,5-dione was prelmred in high yield by heating phenylalanine methyl ester in toluene under reflux. The reduction of this cydodipeptide with sodium NaBH4-BF3 in DIME gave the (2S ,SS)-bis(phenyl-methyl)plperazine, which, on heating with ethylene bromide and triethyiamine, afforded the title compounds. This methodwas proved to be generally applicable to the synthesis of C2-symmetric 2, 5-disubsiituted=l, 4-diazabicyclo [ 2.2.2 ] octanefrom the corresponding natural or unnatural amino acid esters.     

(1S,3S)-1,3-二苯基-1,3-丙二胺的合成

以二氯甲烷作溶剂,N-Boc保护的二氢吡唑在六甲基磷酰胺存在下与苯基格氏试剂反应,比较大量地制备了对应的四氢吡唑(4);再由4合成消旋的1,3-二苯基-1,3-丙二胺(1,总收率35%);1经L-二苯甲酰酒石酸盐拆分制得光学纯的(1S,3S)-1,3-二苯基-1,3-丙二胺,其结构经1HNMR确证。     

Non-radiative transitions. I. S1 ⇝ S0 internal conversion calculations in benzene and deuterobenzene

Non-radiative rate calculations for the S₁ ⇝ S₀ transition are presented. Complete vibrational basis sets are used. A Morse oscillator potential is assumed, for both the ν₁ and ν₂ vibrations. It is shown that the ν₁ potential has a dominant influence on the excess energy behaviour of the rates similar to that of the ν₂. The increase of the normalized non-radiative rate curves with excess energy is consistent with experimental results. A comparison is made with the non-radiative rates determined using the local-mode approximation for the CH- and CD-stretch vibrations.     

微生物酶催化制备人参皂苷20(S)-Rg2,20(S)-Rh1和20(S)-PPT

摘要 人参次级皂苷具有较强的抗癌、抗癌转移等药理活性,但由于在人参中含量少或不存在,因此以人参中含量较高的主要人参皂苷制备药效更高的人参次级皂苷不仅有必要,而且很有意义．本文以微生物Microbacterium esteraromaticum GS514的培养液中分离的粗酶为催化剂水解人参皂苷Re和Rg1,并通过1H NMR和13C NMR谱进行了水解产物的结构表征．实验结果表明,反应体系中无机盐NaCl的存在与否直接影响人参皂苷Re,Rg1与粗酶液的反应结果.人参皂苷与粗酶液直接反应,人参皂苷Re不发生反应,人参皂苷Rg1通过C6所连β-D-吡喃葡萄糖的选择性水解转化成人参皂苷F1.如果该反应是在无机盐NaCl存在下进行,人参皂苷Re通过对C20 所连β-D-吡喃葡萄糖的选择性水解定向转化为20(S)-人参皂苷Rg2;人参皂苷Rg1定向转化成20(S)-人参皂苷Rh1以及20(S)-原人参三醇（PPT）.这说明NaCl的加入激活了C20β-D-吡喃葡萄糖苷酶的活性,这对定向合成不同次级人参皂苷具有重要意义.     

Jet spectroscopy of pyrene complexes: Unusual complexation shifts in the S0 → S1 spectrum

The fluorescence excitation spectra of pyrene complexes with n-alkanes are reported for the S₀ → S₁ and S₀ → S₂ transitions. The S₂ spectral shifts are predictable from theory, and by comparison with other molecules, such as perylene. On the other hand, the S₁ Resonances of pyrene complexes show unusually small displacements from those of the parent species. The spectra of the butane, pentane and hexane complexes actually exhibit net blue shifts. This behaviour provides good evidence for a repulsive interaction in the S₁ state, which is not observed in S₂. Moreover, because the butadiene and benzene complexes give predictable red shifts ⩾ 100 cm⁻¹, and these are found to have plane-parallel geometries, the blue shift correlates with a host carbon—guest hydrogen interaction in the repulsive regime. We also report that the ethylene complex of pyrene exhibits a net blue shift on the S₀ → S₁ transition, and a red shift on S₀ → S₂ only 75% of the predicted value, based on measurements with perylene complexes. This behaviour strongly indicates that ethylene-pyrene has a T-shaped configuration, as predicted by potential energy calculations.     

S1←S0 vibronic spectra and the vapor-state molecular structure of propanal and 2-methylpropanal

The vapor-state absorption spectra have been recorded for propanal PA and 2-methylpropanal MP with path lengths up to 120 m. The initial points in the S₁S₀ electronic transitions have been identified together with various fundamental vibrational frequencies of the PA and MP conformers. They contain nonplanar aldehyde groups in the S₁ states with inversion potential barriers of about 600 cm^–1. The parameters of the internal-rotation potential functions in the S₁ states have been determined, and the corresponding potential functions in the S₀ states have been refined.Chemical Faculty, Lomonosov Moscow University. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 1, pp. 20–25, January–February, 1993.     

Overlapping resonances interference-induced transparency: The S(0) → S(2)∕S(1) photoexcitation spectrum of pyrazine

The phenomenon of "overlapping resonances interference-induced transparency" (ORIT) is introduced and studied in detail for the S(0) → S(2)∕S(1) photoexcitation of cold pyrazine (C(4)H(4)N(2)). In ORIT, a molecule becomes transparent at specific wavelengths due to interferences between envelopes of spectral lines displaying overlapping resonances. An example is the S(2)???S(1) internal conversion in pyrazine where destructive interference between overlapping resonances causes the S(0) → S(2)∕S(1) light absorption to disappear at certain wavelengths. ORIT may be of practical importance in multi-component mixtures where it would allow for the selective excitation of some molecules in preference to others. Interference-induced cross section enhancement is also shown.