New Approaches to the Use of Amino Acids as Chiral Building Blocks in Organic Synthesis [New Synthetic Methods (85)]

α-Amino acids protected at nitrogen in quite different ways can be transformed without racemization into the corresponding α-amino aldehydes. Provided one chooses the right protecting groups (e.g., two benzyl residues on nitrogen) it is possible for the first time to carry out Grignard-like, aldol, and Me₃SiCN additions, and hetero-Diels–Alder reactions with a high degree of nonchelation control. If the reactions of classical carbanions turn out to be nonselective, transmetalation, for example into organotitanium reagents, constitutes an important tool in controlling stereoselectivity. Diastereoselectivity can be reversed by specific variation of the protecting group and reagent. “Protecting-group tuning”, “metal tuning”, and “ligand tuning” are very useful in reactions of α-amino aldimines as well. The α-amino aldehydes can also be converted by Wittig reactions into electron-poor γ-amino olefins, which in turn undergo stereoselective cuprate, Michael, and cycloadditions.     

Alkoxysulfanes AlkylO-S-Y as Building Blocks and Ligands

Abstract

The Thio-ARBUZOV-Reactions has proved to be a facile synthetic route for the conversion of alkoxysulfanes into sulfinyl derivatives. Scope and limitations of the reaction are discussed. BEcause of their donor properties the alkoxysulfanes are suitable ligands which has been confirmed by the preparatoin of palladium(II) complexes.     

一类新的多功能构筑基块-多吡唑化合物的设计合成

The design and synthesis of novel polypyrazolyl aromatic bridging ligands 1,3,5-tris（3,5-dimethyl-1-pyrazol-4-yl）benzene and 2,4,6-tris（4-（3,5-dimethyl-^1H-pyrazol-4-yl）phenyl）-1,3,5-triazine from simple starting materials mesitylene and p-tolunitrile were reported.     

多金属氧酸盐作为构筑块自组装合成新型功能性分子材料

本文概述了以多金属氧酸盐为构筑块合成新型功能性分子材料的研究状况和新进展 ,对这类化合物在催化、导电性、磁性和LB膜等方面的应用前景作了评述和展望     

Superhalogens as Building Blocks of Super Lewis Acids

Lewis acids play an important role in synthetic chemistry. Using first-principle calculations on some newly designed molecules containing boron and organic heterocyclic superhalogen ligands, we show that the acid strength depends on the charge of the central atom as well as on the ligands attached to it. In particular, the strength of the Lewis acid increases with increasing electron withdrawing power of the ligand. With this insight, we highlight the importance of superhalogen-based ligands in the design of strong Lewis acids. Calculated fluoride ion affinity (FIA) values of B[C₂BNO(CN)₃]₃ and B[C₂BNS(CN)₃]₃ show that these are super Lewis acids.     

Active Ester Functionalized Azobenzenes as Versatile Building Blocks

Azobenzenes are important molecular switches that can still be difficult to functionalize selectively. A high yielding Pd-catalyzed cross-coupling method under mild conditions for the introduction of NHS esters to azobenzenes and diazocines has been established. Yields were consistently high with very few exceptions. The NHS functionalized azobenzenes react with primary amines quantitatively. These amines are ubiquitous in biological systems and in material science.     

Cyclodextrins as Building Blocks for Supramolecular Structures and Functional Units

Cyclodextrins are frequently used as building blocks, because they can be linked both covalently and noncovalently with specificity. Thus one, two, three, seven, fourteen, eighteen, or twenty substituents have been linked to one β-cyclodextrin molecule in a regioselective manner. Furthermore, Cyclodextrins may serve as organic host molecules. Their internal cavity is able to accommodate one or two guest molecules. Conversely, suitable guest molecules can be used to thread one, two, or many (one hundred or more) cyclodextrin rings. The resulting supramolecular structures are often formed in solution, which allows characterization by high-resolution spectroscopic methods. Chemical conversion of these structures provides molecular architectures such as catenanes, rotaxanes, polyrotaxanes, and tubes, which are not readily prepared by other methods. The particular properties of Cyclodextrins can also be employed, for example, for the chromatographic separation of complex mixtures of substances, even racemates, by molecular recognition. Cyclodextrins and their derivatives have been found to be remarkably active catalysts as well. Finally, since Cyclodextrins can favorably influence the release of drugs, many new applications will certainly be developed in the near future.     

Tetrathiafulvalene-functionalized Cavitands as Building Blocks for Redox Active Hemicarcerands

Two new cavitands bearing four upper-rim tetrathiafulvalene (TTF) units were synthesized. One of these cavitands was used to prepare a redox-active hemicarcerand containing four TTF subunits covalently appended to its equatorial region. Preliminary electrochemical characterization data show that the four TTF residues in all these compounds behave as independent, non-interacting groups in their heterogeneous electron transfer reactions.     

Naphthalene Disaccharide Fragments as Building Blocks for Angucycline Synthesis

ABSTRACT

Methods for the construction of naphthalene oligodeoxy disaccharide fragments, common structural elements of the angucycline antibiotics, are investigated. The triphenylphosphonium bromide- or scandium triflate-catalyzed addition of rhodinal to 4-OH silyl-protected olivoses affords the required 3-O-α-oligodeoxy disaccharides selectively and in high yields.     

Polyoxometalates as Inorganic Building Blocks of Multifunctional Molecular Materials

The use of polyoxometalates (pOM's) as inorganic component in the synthesis of new molecular hybrid materials is presented. Here we show that the combination of organic molecules of the tetrathiafulvalene (TTF) type or perylene (per) with POM's yields new radical salts with unprecedented structures that present interesting magnetic and/or electrical properties or coexistence of both. The first true metallic radical salt containing a POM has been prepared and characterized. We also describe the recent results obtained by combining magnetic POM's with the organometallic cation decamethylferrocene.     

Carbohydrate-Derived Dienes as Building Blocks for Pharmaceutically Relevant Molecules

Carbohydrate-based dienes are valuable building blocks for a variety of highly functionalized carbo- and oxa-cycles by virtue of their high degree of inherent stereochemical information, and suitability in various synthetic transformations. Research into the chemistry of carbohydrate-based dienes has been expanding over the last decades due to its unique applications in the construction of diverse and complex structural frameworks. In this review, we describe the main transformations of this interesting class of molecule and highlight their utility in the construction of diverse ring systems important for drug development.     

Ketenimine Complexes from Carbene Complexes and Isocyanides: Versatile Building Blocks for Carbocycles and N-Heterocycles [New Synthetic Methods (74)]

Ketenimine complexes are readily available in great variety by reaction of isocyanides with carbene complexes. They have proven to be useful building blocks in new synthetic approaches to carbocyclic and N-heterocyclic four-, five-, and six-membered rings. The reactions involve new metal-induced bond formation patterns of the ketenimine ligands, which can be influenced across a wide range by varying the following five parameters: the metal, the ligands, and the three substituents on the N?C?C unit.     

Reactions Using Freons and Halothane as Halofluoroalkyl/Halofluoroalkenyl Building Blocks

In recent years, hydrofluorocarbon compounds such as chlorofluorocarbons, hydrochlorofluorocarbons, and 2-bromo-2-chloro-1,1,1-trifluoroethane (halothane) have been used as fluorine-containing building blocks to construct functional fluorine-containing compounds, e. g., polymers, liquid crystals, and medicines. Hydrofluorocarbons promote the formation of reactive fluoroalkyl or fluoroalkenyl species via anionic or radical processes, and these species can act as nucleophiles or electrophiles depending on the reaction conditions. Progress in fluorine chemistry using hydrofluorocarbons in the last 30 years is described in this review and diverse reactions are discussed, including the fluoroalkyl/alkenyl products and proposed mechanisms involved.     

Heterometallic Rings: Their Physics and use as Supramolecular Building Blocks

An enormous family of heterometallic rings has been made. The first were Cr₇M rings where M=Ni^II, Zn^II, Mn^II, and rings have been made with as many as fourteen metal centers in the cyclic structure. They are bridged externally by carboxylates, and internally by fluorides or a penta‐deprotonated polyol. The size of the rings is controlled through templates which have included a range of ammonium or imidazolium ions, alkali metals and coordination compounds. The rings can be functionalized to act as ligands, and incorporated into hybrid organic–inorganic rotaxanes and into molecules containing up to 200 metal centers. Physical studies reported include: magnetic measurements, inelastic neutron scattering (including single crystal measurements), electron paramagnetic resonance spectroscopy (including measurements of phase memory times), NMR spectroscopy (both solution and solid state), and polarized neutron diffraction. The rings are hence ideal for understanding magnetism in elegant exchange‐coupled systems.