超大硅胺基氯锗宾的反应性与立方四锗卡宾的成键解析

超大硅胺基取代的低价锗化合物可以构建新颖的化学结构,提供有学术价值的新发现。二配位的超大硅胺基氯锗宾Ge(N(SiⁱPr₃)₂)Cl (1)具有空的4p轨道和孤电子对。针对这2个特点,研究了化合物1的热构型转换和菲醌氧化加成反应。1的温热分解生成了立方四锗卡宾 Ge₄(NSiⁱPr₃)₄ (2),与菲醌(L)定量氧化加成生成了胺基一氯菲二酚合锗(Ⅳ)：[Ge(N(SiⁱPr₃)₂)(L)Cl] (3)。表征了2个产物的单晶结构与组成。四锗卡宾2本质上是锗异腈的四聚体,分子呈现出畸变的立方体构型,4个Ge原子和4个N原子构成了中心立方体的 8个顶点。其中 Ge—N键长为 0.203 6(3) nm,N—Ge—N与 Ge—N—Ge的键角分别为 85.51(18)°和94.32(16)°,立方体的侧面接近平行四边形。理论计算首次揭示了四锗卡宾2的成键面貌。自然键轨道(NBO)给出Ge₄N₄骨架上的20个分子轨道。轨道定域化的计算结果完好地呈现出4对Ge孤对电子、12个Ge—N键和4个Si—N键的定域轨道,能量分别为-12.22、-15.12 和-20.12 eV。Ge 孤对电子主要保留了 4s 电子的特性,而 Ge—N 键主要由 N 的 2s 轨道(18.4%)和 2p 轨道(71.3%)、Ge的4s轨道(0.75%)和4p轨道(9.43%)综合贡献形成。在化合物3的分子中,Ge^Ⅳ采取sp³杂化,由于空间位阻与非对称配位,与另外4个配位原子形成非对称四面体构型。     

钛开环夹心羰基化合物的构象分析

合成了３个钛开环夹心羰基化合物．用１ＨＮＭＲ方法对３个钛开环夹心羰基化合物进行了研究实验结果表明,钛开环夹心羰基化合物的分子构象与开环配体的取代状况有关．由对称取代戊稀基配体形成的化合物只有１种构象,由非对称取代戊二稀基［２ＣＨ３Ｃ５Ｈ６］－形成的化合物具有２种构象（ｃｉｓ和ｔｒａｎｓ）．     

Stereoselective synthesis and absolute configuration of the C33-C42 fragment of symbiodinolide

Cross-metathesis of methyl ester which was prepared from symbiodinolide with ethylene was performed to give the C33-C42 degraded fragment. This fragment was estimated to be (36S,40S)-diol by the modified Mosher method. Stereoselective synthesis of the (36S,40S)-diol and its diastereomer (36R,40S)-diol was achieved from l-aspartic acid. Synthetic bis-(S)- and (R)-MTPA esters which were derivatized from the (36S,40S)-diol exhibited spectroscopic data identical with those of bis-(S)- and (R)-MTPA esters derived from the degraded product. Thus, the absolute stereochemistry of the C33-C42 fragment was elucidated to be (36S,40S).     

Regulating Oxygen Configuration in Hierarchically Porous Carbon Nanosheets for High-Rate and Durable Na+ Storage

Surface oxygen functionalities (particularly C−O configuration) in carbon materials have negative influence on their electrical conductivity and Na⁺ storage performance. Herein, we propose a concept from surface chemistry to regulate the oxygen configuration in hierarchically porous carbon nanosheets (HPCNS). It is demonstrated that the C−O/C=O ratio in HPCNS reduces from 1.49 to 0.43 and its graphitization degree increases by increasing the carbonization temperature under a reduction atmosphere. Remarkably, such high graphitization degree and low C−O content of the HPCNS-800 are favorable for promoting its electron/ion transfer kinetics, thus endowing it with high-rate (323.6 mAh g⁻¹ at 0.05 A g⁻¹ and 138.5 mAh g⁻¹ at 20.0 A g⁻¹) and durable (96 % capacity retention over 5700 cycles at 10.0 A g⁻¹) Na⁺ storage performance. This work permits the optimization of heteroatom configurations in carbon for superior Na⁺ storage.     

亲核性1,2-重排为何迁移基团的构型保持不变*

亲核性1,2-重排反应是有机化学的重要反应之一,重排中离去基团的离去和迁移基团的迁移步骤既可以是分步的,也可以是协同的,但是迁移基团的构型始终保持不变。本文用超共轭效应和反应过程中有机立体电子效应解释了此现象,掌握一般规律,希望能够从教学上便于教师讲授和学生学习理解。     

Asymmetric Total Syntheses,Stereostructures, and Cytotoxicities of Marine Bromotriterpenoids Aplysiol B (Laurenmariannol) and Saiyacenol A

There are marine cytotoxic bromotriterpenoids, named the thyrsiferol family that are structurally characterized by some tetrahydropyran (THP) and tetrahydrofuran (THF) rings. The thyrsiferol family belongs to natural products that are often difficult to determine their stereostructures even by the current, highly advanced spectroscopic methods, especially in acyclic systems including stereogenic tetrasubstituted carbon centers. In such cases, it is effective to predict and synthesize the possible stereostructures. Herein, to elucidate ambiguous stereostructures and unassigned absolute configurations of aplysiol B, laurenmariannol, and saiyacenol A, members of the thyrsiferol family, we carried out their asymmetric chemical syntheses featuring 6-exo and 5-exo oxacyclizations of epoxy alcohol precursors and 6-endo bromoetherification of a bishomoallylic alcohol. In this paper, we report total assignments of their stereostructures through their asymmetric chemical syntheses and also their preliminary cytotoxic activities against some tumor cells. These results could not have been achieved without depending on asymmetric total synthesis.     

Using Terpene Synthase Plasticity in Catalysis: On the Enzymatic Conversion of Synthetic Farnesyl Diphosphate Analogues

Four synthetic farnesyl diphosphate analogues were enzymatically converted with three bacterial sesquiterpene synthases, including β-himachalene synthase (HcS) and (Z)-γ-bisabolene synthase (BbS) from Cryptosporangium arvum, and germacrene A synthase (SmTS6) from Streptomyces mobaraensis. These enzyme reactions not only yielded several previously unknown compounds, showing that this approach opened the door to a new chemical space, but substrates with blocked or altered reactivities also gave interesting insights into the cyclisation mechanisms and the potential to catalyse reactions with different initial cyclisation modes.