Stereoselective allyl amine synthesis through enantioselective addition of diethylzinc and [1,3]-chirality transfer: synthesis of lentiginosine and polyoxamic acid derivative

A new synthetic method for the preparation of allyl amines has been developed. The key steps of this method are enantioselective addition of diethylzinc and [1,3]-chirality transfer through the [3.3] sigmatropic rearrangement of allyl cyanates. Stereocontrolled syntheses of lentiginosine (1) and polyoxamic acid derivative 2 from a common intermediate 7 derived from D-tartaric acid (8), have been accomplished.     

Beyond PEG2000: Synthesis and Functionalisation of Monodisperse PEGylated Homostars and Clickable Bivalent Polyethyleneglycols

A new strategy to access highly monodisperse, heterobifunctional linear polyethylenglycols (PEGs) has been designed. This was built around unidirectional, iterative chain extension of a 3‐arm PEG homostar. A mono‐(4,4′‐dimethoxytriphenylmethyl) octagol building block, DmtrO‐EG₈‐OH, was constructed from tetragol. After six rounds of chain extension, the monodisperse homostar reached the unprecedented length of 56 monomers per arm (PEG2500). The unique architecture of the synthetic platform greatly assisted in facilitating and monitoring reaction completion, overcoming kinetic limitations, chromatographic purification of intermediates, and analytical assays. After chain terminal derivatisation, mild hydrogenolytic cleavage of the homostar hub provided heterobifunctional linear EG₅₆ chains with a hydroxyl at one end, and either a toluene sulfonate, or a tert‐butyl carboxylate ester at the other. A range of heterobifunctional, monodisperse PEGs was then prepared having useful cross‐linking functionalities (‐OH, ‐COOH, ‐NH₂, ‐N₃) at both ends. A rapid preparation of polydisperse PEG homostars, free of multiply cross‐linked chains, is also described. The above approach should be extendable to other high value oligomers and polymers.     

Substrate‐Controlled Asymmetric Total Syntheses of Microcladallenes A,B, and C Based on the Proposed Structures

Substrate‐controlled asymmetric total syntheses of (+)‐microcladallenes A, B, and C have been accomplished based on the proposed structures. The syntheses of microcladallenes A and B confirmed the structures and absolute configurations of both natural products. However, the synthesis of microcladallene C, which includes seven stereogenic centers and an (R)‐bromoallene in its compact C₁₅ framework, brought the realization that its proposed structure must be revised. The introduction of C12‐bromine into these natural products with retention of configuration relied on TiBr₄‐mediated nucleophile‐assisting leaving group brominations, the stereochemical outcome of which could be attributed, at least in part, to an oxonium or halonium ion formation–fragmentation sequence through intricate neighboring group participation. In addition, the pivotal β‐oriented vicinal cis‐dichloride function in microcladallene C was elaborated through a novel tandem Cl₂‐induced electrophilic cyclization/imidate chlorination process. The positive rotations of these natural products with an (R)‐bromoallene constitute exceptions to Lowe’s rule for reasons yet to be determined.     

From nanographene and graphene nanoribbons to graphene sheets: chemical synthesis

Graphene, an individual two-dimensional, atomically thick sheet of graphite composed of a hexagonal network of sp(2) carbon atoms, has been intensively investigated since its first isolation in 2004, which was based on repeated peeling of highly oriented pyrolyzed graphite (HOPG). The extraordinary electronic, thermal, and mechanical properties of graphene make it a promising candidate for practical applications in electronics, sensing, catalysis, energy storage, conversion, etc. Both the theoretical and experimental studies proved that the properties of graphene are mainly dependent on their geometric structures. Precise control over graphene synthesis is therefore crucial for probing their fundamental physical properties and introduction in promising applications. In this Minireview, we highlight the recent progress that has led to the successful chemical synthesis of graphene with a range of different sizes and chemical compositions based on both top-down and bottom-up strategies.     

离子液体的合成与功能化设计

作为一种新型低污染的绿色溶剂,离子液体近来受到多方关注。文章综述了离子液体合成和功能化设计方面的研究进展,微波和超声波辅助合成离子液体与常规方法相比所需反应时间短、产率高,表现出一定优势。     

A Case for Bond‐Network Analysis in the Synthesis of Bridged Polycyclic Complex Molecules: Hetidine and Hetisine Diterpenoid Alkaloids

A key challenge in the synthesis of diterpenoid alkaloids lies in identifying strategies that rapidly construct their multiply bridged polycyclic skeletons. Existing approaches to these structurally intricate secondary metabolites are discussed in the context of a “bond‐network analysis” of molecular frameworks, which was originally devised by Corey some 40 years ago. The retrosynthesis plans that emerge from a topological analysis of the highly bridged frameworks of the diterpenoid alkaloids are discussed in the context of eight recent syntheses of hetidine and hetisine natural products and their derivatives. This Minireview highlights the extent to which network analyses of the type described here sufficed for designing synthesis plans, as well as areas where they had to be amalgamated with functional group oriented synthetic planning considerations.     

Total and Semi‐Syntheses of Antimicrobial Thuggacin Derivatives

The total and semi‐synthesis of 13 new macrolactones derived from thuggacin, which is a secondary metabolite from the myxobacterium Sorangium cellulosum, are reported. The thuggacins have attracted much attention due to their strong antibacterial activity, particularly towards Mycobacterium tuberculosis. This study focuses on 1) thuggacin derivatives that cannot equilibrate by transacylation between the three natural thuggacins A–C, 2) the roles of the thiazole ring, and 3) the hexyl side chain at C2. Semi‐synthetic O‐methylation at C17 suppressed the transacylations without a substantial loss of antibacterial activity. Exchanging the C17–C25 side chain for simplified hydrophobic chains led to complete loss of antibacterial activity. Exchange of the thiazole by an oxazole ring or removal of the hexyl side chain at C2 had no substantial effect on the biological properties.     

纳米材料在超级电容器领域的有效设计与可控合成

伴随着电化学储能器件在便携式电子产品、混合动力电动汽车及大型工业规模的电力和能源管理中的应用,设计合成出结构新颖、性能优越的先进纳米电极材料显得至关重要.作为电化学储能器件中的重要一员,超级电容器以其功率密度高、循环寿命长等特点越来越受到人们的广泛关注,而电极材料的组成及结构是其性能高低的决定性因素.本文结合本科研团队近几年来的研究工作,综述了有关超级电容器纳米电极材料的设计与可控合成及其前沿研究进展.     

Synthesis of Boswellic Acid Derivatives and Primary Research on their Activities

In order to search for new potent anti-cancer agents, a series of boswellic acid derivatives were designed and synthesized. Six of them were identified by IR, NMR and MS as new compounds and biologic assay of anti-cancer is underway.     

Asymmetric Total Synthesis of Oxazolomycins B and C

Efforts towards the first total synthesis of (−)-oxazolomycin B and (+)-oxazolomycin C from the intermediate of our previous synthesis of (+)-neoxazolomycin are reported. The syntheses were achieved in a longest linear sequence of 25 steps from the amino acid serine in 3.6 and 2.7 % overall yields, respectively. The efficiency of our approach is derived from silyl triflate-mediated reductive oxazolidine ring-opening and Fürstner's Ru-catalyzed hydrosilylation and protodesilylation reactions. The obtained spectra and optical rotations were in good agreement with those of natural products, thus confirming the structures.     

Synthesis of Cyclobakuchiols A,B, and C by Using Conformation‐Controlled Stereoselective Reactions

Cyclohexanone with the pMeOC₆H₄ and CH₂?C(Me) substituents at the C3 and C4‐positions was prepared from (+)‐β‐pinene and converted to the allylic picolinate by a Masamune–Wittig reaction followed by reduction and esterification. Allylic substitution of this picolinate with Me₂CuMgBr ? MgBr₂ in the presence of ZnI₂ proceeded with γ regio‐ and stereoselectively to afford the quaternary carbon center on the cyclohexane ring with the CH₂?CH and Me groups in axial and equatorial positions, respectively. This product was converted to cyclobakuchiol A by demethylation and to cyclobakuchiol C by epoxidation of the CH₂?C(Me) group. For the synthesis of cyclobakuchiol B, the enantiomer of the above cyclohexanone derived from (?)‐β‐pinene was converted to the cyclohexane‐carboxylate, and the derived enolate was subjected to the reaction with CH₂?CHSOPh followed by sulfoxide elimination to afford the intermediate with the quaternary carbon center with MeOC(?O) and CH₂?CH groups in axial and equatorial positions. The MeOC(?O) group was transformed to the Me group to complete the synthesis of cyclobakuchiol B.     

Chemoselectivity and the Curious Reactivity Preferences of Functional Groups

Achieving high levels of chemoselectivity has been the Achilles’ heel of chemical synthesis. The excitement generated by the successful realization of chemoselective strategies underscores the painstaking efforts to define a set of conditions conducive to selection among the available reaction pathways. We discuss in this Review various aspects of chemoselectivity that have been addressed in a range of synthetic methods over the past decade. We have focused on the proposed mechanistic basis of the reactions under consideration in an attempt to categorize them and highlight the key concepts that have been emerging on the basis of these studies. Our overview of recent advances in chemoselective processes suggests that significant progress has been made, but a lot of challenges lie ahead.     

A Strategy for the Preparation of Thioantimonates Based on the Concept of Weak Acids and Corresponding Strong Bases

By following a new synthetic approach, which is based on the in situ formation of a basic medium by the reaction between the strong base Sb(V)S₄^3? and the weak acid H₂O, it was possible to prepare three layered thioantimonate(III) compounds of composition [TM(2,2′‐bipyridine)₃][Sb₆S₁₀] (TM=Ni, Fe) and [Ni(4,4′‐dimethyl‐2,2′‐bipyridine)₃][Sb₆S₁₀] under hydrothermal conditions featuring two different thioantimonate(III) network topologies. The antimony source, Na₃SbS₄ ? 9 H₂O, undergoes several decomposition reactions and produces the Sb^IIIS₃ species, which condenses to generate the layered anion. The application of transition‐metal complexes avoids crystallization of dense phases. The reactions are very fast compared to conventional hydrothermal/solvothermal syntheses and are much less sensitive to changes of the reaction parameters.     

De Novo Synthesis of Mono‐ and Oligosaccharides via Dihydropyran Intermediates

The importance of carbohydrates is evident by their essential role in all living systems. Their syntheses have attracted attention from chemists for over a century. Most chemical syntheses in this area focus on the preparation of carbohydrates from naturally occurring monosaccharides. De novo chemical synthesis of carbohydrates from feedstock starting materials has emerged as a complementary method for the preparation of diverse mono‐ and oligosaccharides. In this review, the history of de novo carbohydrate synthesis is briefly discussed and particular attention is given to methods that address the formation of glycosidic bonds for potential de novo synthesis of oligosaccharides. Almost all methods of this kind involve the formation of dihydropyran intermediates. Recent progress in forming dihydropyrans by Achmatowicz rearrangement, hetero‐Diels–Alder cycloaddition, ring‐closing metathesis, and other methods is also elaborated.     

超级材料--高维分子基铁磁体的设计与合成

高维分子基铁磁体的设计与合成是自然界向化学家的挑战。本文在简述了高维分子基铁磁体的重要性后,侧重介绍了设计与合成高维磁体的常用桥基、合成方法以及最新研究进展。     

Synthesis and modification of silicon nanosheets and other silicon nanomaterials

Silicon nanomaterials and nanostructures exhibit different properties from those of bulk silicon materials based on quantum confinement effects. They are expected to lead to the development of new applications of silicon, in addition to wide use in semiconductor devices. Aside from industrial interest, intriguing issues of academic interest still remain with respect to the origins of their characteristic properties. Zero- and one-dimensional crystalline silicon nanomaterials have been synthesized, to date, by using many methods and there has been rapid progress in size control and modification procedures. However, there have been only a few examples of silicon nanomaterials with atomic-order thickness akin to carbon nanomaterials, such as two-dimensional silicon nanosheets. Moreover, mass production of silicon nanomaterials with relatively low cost is not easily achievable, due to the typically severe conditions required for fabrication, such as high temperature and ultralow pressure. Recently, we have developed a soft synthetic method for silicon nanosheets with chemical surface modification in a solution process. This review provides methods for the synthesis and modification of silicon nanosheets and other silicon nanomaterials with examples of their potential applications.