Ring‐Opening Reactions of 3‐Aryl‐1‐benzylaziridine‐2‐carboxylates and Application to the Asymmetric Synthesis of an Amphetamine‐Type Compound

Nucleophilic ring‐opening reactions of 3‐aryl‐1‐benzylaziridine‐2‐carboxylates were examined by using O‐nucleophiles and aromatic C‐nucleophiles. The stereospecificity was found to depend on substrates and conditions used. Configuration inversion at C(3) was observed with O‐nucleophiles as a major reaction path in the ring‐opening reactions of aziridines carrying an electron‐poor aromatic moiety, whereas mixtures containing preferentially the syn‐diastereoisomer were generally obtained when electron‐rich aziridines were used (Tables 1–3). In the reactions of electron‐rich aziridines with C‐nucleophiles, S_N2 reactions yielding anti‐type products were observed (Table 4). Reductive ring‐opening reaction by catalytic hydrogenation of (+)‐trans‐(2S,3R)‐3‐(1,3‐benzodioxol‐5‐yl)aziridine‐2‐carboxylate (+)‐trans‐ 3c afforded the corresponding α‐amino acid derivative, which was smoothly transformed into (+)‐tert‐butyl [(1R)‐2‐(1,3‐benzodioxol‐5‐yl)‐1‐methylethyl]carbamate((+)‐ 14 ) with high retention of optical purity (Scheme 6).     

Synthesis and Crystal Structure of Lithium Tetrametaphosphimate Tetrahydrate Li4(PO2NH)4 · 4 H2O

Single crystals of Li₄(PO₂NH)₄ · 4 H₂O were obtained by dissolving LiOH and H₄(PO₂NH)₄ · 2 H₂O in water and subsequent precipitation with acetone and ethanol followed by slow evaporation of the solvents. The structure of Li₄(PO₂NH)₄ · 4 H₂O was solved by single‐crystal X‐ray methods ( (No. 2), a = 489.2(2), b = 853.2(2), c = 880.5(2) pm, α = 101.71(3), β = 102.39(3), γ = 94.88(3)°, Z = 1). The structure is composed of LiO₄ tetrahedra and (PO₂NH)₄^4? ions. The P₄N₄ rings of the anions exhibit a slightly distorted chair–1 conformation, which is supported by IR data and has been described by torsion angles, displacement asymmetry parameters and puckering parameters. Via Li⁺ ions and hydrogen bonds, the tetrametaphosphimate anions are connected forming a three‐dimensional network.     

旋转薄层色谱分离聚合物

报道了旋转薄层色谱分级聚合物，及配合直接扫描密度法测定分子量分布的结果．在旋转薄层硅胶板上用混合溶剂成功地分离并直接收集了聚苯乙烯２１个级分，分子量测定结果与ＧＰＣ法基本一致．初步认为旋转薄层色谱以薄层吸附色谱分离机理为基础，采用连续注入流动相和旋转薄层板离心力相结合的方式，改善并加快了分离效果     

Ring strain energies: substituted rings, norbornanes, norbornenes and norbornadienes

Ring strain energies (RSEs) are predicted using homodesmotic reactions at the B3LYP/6-31G^* level of theory. Substituents are conserved in the acyclic reference and any difference in energy between the ring and the acyclic reference corresponds exclusively to RSE. Small rings are stabilized by alkyl substituents and this stabilization decreases as the size of the ring increases. There is a destabilization of medium sized rings. Greater stabilization is found upon alkyl substitution at a double bond in an unsaturated ring and this stabilization decreases as ring size increases. The effects of cis-1,2-disubstitution on RSEs have been evaluated and indicate stabilization for both small and medium sized rings. RSEs of saturated and unsaturated polycyclic systems agree well with the RSEs derived from experimental thermochemical data. RSEs are reported for substituted norbornanes, norbornenes, and norbornadienes to complement experimental studies.     

化学位移估算研究ATP构象随溶液pH值的变化

利用Johnson和Bovey的理论和方法计算了不同扭曲角χ(O4′－C1′－N9－C4)的ATP(5′-三磷酸腺苷)分子中糖环质子H1′和H2′由于环流效应引起的化学位移.H1′的化学位移与扭曲角χ有较强的依赖关系,反映了ATP在溶液中细微的构象变化.将计算结果与实验结果比较,证明在本文讨论的pH值范围(1～10)内,Mg2＋加入后,ATP的扭曲角χ在230～360°范围内变化.随溶液的pH值减小,ATP分子的构象由trans 构象通过-gauche构象转变为cis构象. 从而证明在酸性条件下, ATP倾向于以cis构象存在,而在碱性条件下trans构象更为稳定,从另一方面支持了在酸性条件下N1参与配位而在碱性条件下N7参与配位的结论.在讨论中也考虑了由pH变化所引起的环流强度的变化.     

Stereoselective synthesis of the octahydroisobenzofuran skeleton of the eunicellins

A de novo asymmetric synthesis of the octahydroisobenzofuran skeleton contained within the eunicellin family of natural products has been completed. The key transformations involve the convergent assembly of a tetrasubstituted tetrahydrofuran by condensation of a functionalised allylsiloxane with an aldehyde; controlled epimerisation of a C4 aldehyde by intramolecular trapping; installation of the isopropyl substituent by stereoselective Michael addition to a 5,5-bicyclic enone; and ring expansion of the 5,5-system to the target structure by radical-mediated cyclopropane fragmentation.     

二(芳氧基)稀土(Ⅱ)配合物催化ε-己内酯开环聚合

系统地研究了二（２，６ 二叔丁基 ４ 甲基酚基）钐［（ＡｒＯ）２Ｓｍ（ＴＨＦ）４］催化ε 己内酯的开环聚合，发现它具有很高的催化活性并显示“活性”聚合的特点，在甲苯中，当［Ｍ］／［Ｉ］＝２０００（摩尔比），６０℃，１ｈ，转化率可达９８％．并比较了不同的两价稀土化合物的催化活性．通过核磁分析末端基结构的方法，研究了（ＡｒＯ）２Ｓｍ催化己内酯开环聚合的引发机理，发现催化剂首先与己内酯反应，生成三价烯醇式稀土化合物，后者引发己内酯聚合．     

Acetyltrimethylsilane mediated synthesis of dihydrophenanthrenes

An easy and efficient synthesis of phenanthrene derivatives through base catalyzed ring transformation of 4-sec-amino-2-oxo-5,6-dihydro-2H-benzo[h]chromene-3-carbonitriles with acetyltrimethylsilane is described in good yields. The advantage of this reaction is the direct transformation of 2-oxobenzo[h]chromene into phenanthrene via C-C insertion from acetyltrimethylsilane.     

Iodocyclization/base-induced hydrodeiodination reaction of 5-substituted 4-alkenols. The influence of substituent on the stereoselective pathway

The electrophilic iodocyclization reaction of (Z)- and (E)-5-n-alkylsubstituted 4-alken-1-ols followed by base-induced hydrodeiodination reaction stereoselectively gave, respectively, (Z)- and (E)-alkylidentetrahydrofurans in high yield. Completely different outcomes were observed with (Z)- and (E)-6,6-dimethylhept-4-en-1-ol: their iodocyclization furnished, respectively, threo- and erythro-2-(1-iodo-2,2-dimetylpropyl)tetrahydrofuran with high stereoselectivity. The threo isomer gave clean formation of 6-tert-butyl-3,4-dihydro-2H-pyran by base-induced ring expansion, while erythro isomer underwent a base-induced ring contraction to 1-cyclopropyl-3,3-dimethylbutan-1-one. Moreover, (Z)- and (E)-5-cyclopropylpent-4-en-1-ol underwent a 6-endo-iodocyclization to threo- and erythro-2-cyclopropyl-3-iodotetrahydro-2H-pyran, respectively, that under the same basic treatment, gave two isomeric 6-cyclopropyldihydro-2H-pyrans in a stereoselective fashion.     

Untersuchungen von Reaktionsmechanismen durch Isotopenmarkierung,IX Zum Ringverengungsmechanismus von 1,4-Benzthiazin-2,3-4H-dion

By¹⁴C-labeling it is shown that the ring contraction reaction of 1,4-benzothiazin-2,3-4H-dione (1), leading via benzthiazol-2-carbonic acid (2) finally to benzthiazole (3), proceeds via hydrolytic opening of the thiolactone-bond in1, irrespectively of H⁺ or OH^– catalysis.