A general approach to triphenylenes and azatriphenylenes: total synthesis of dehydrotylophorine and tylophorine

A convergent and flexible synthesis of substituted triphenylenes, azatriphenylenes, and the cytotoxic alkaloids dehydrotylophorine and tylophorine has been developed.     

Cyclization strategies for the synthesis of macrocyclic bisindolylmaleimides

Three new approaches to the synthesis of macrocyclic bisindolylmaleimides 1-4 have been identified. Two strategies afford 8, the penultimate intermediate for the synthesis of 1-4, in 73% and 32% yield by intramolecular cyclization of 31 and 40, respectively. The optimum synthesis of 1 was achieved in nine steps and 15% yield by intramolecular formation of the macrocycle and maleimide in one step by reaction of the sodium indolate of 12 with methyl indole-3-glyoxylate 47. The mechanism of this reaction has been elucidated, using the trityl-protected derivative, to involve initial formation of the tricarbonyl imide 48, followed by irreversible alkylation of the indole nitrogen to generate the 17-membered macrocycle 49. Cyclization of 49 to hydroxymaleimide 50 and subsequent dehydration afforded 8a. This approach eliminated the problem of dimerization observed in the intramolecular cyclization reactions.     

New strategies for the synthesis of pyrimidine derivatives

Recent advances in pyrimidine synthesis are described. Modification of conventional strategies involving N-C-N fragment condensation with 1,3-dicarbonyl derivatives remains a common theme in current literature. Other methods, including N-C fragment condensation strategies, provide reactive intermediates capable of intramolecular cyclization and formation of pyrimidine derivatives. These recently developed methodologies offer a valuable addendum to azaheterocycle synthesis.     

Diastereodivergent strategies for the synthesis of homochiral aculeatins

We report concise and stereocontrolled syntheses of aculeatins (-)-A, (+)-B, (+)-D, and (+)-6-epi-D. Diastereodivergent 1,3-inductions in Mukaiyama aldol coupling contribute to reduce steps and to increase flexibility with reactants having sterically restricted proximal substituents (i.e., CH2), involving either a good anti or a moderate syn 1,3-induction, depending on the nature of protecting group (P). In addition, the 3,5-syn-diol-ketone resulting from concomitant deprotection of the beta-alkoxy (Tr = trityl) group proves to be remarkably stable whereas the 3,5-anti diastereoisomer cyclizes spontaneously to the corresponding tetrahydropyran hemiketal, thus enabling a useful and facile separation. The second part of our study is devoted to improving the yield and the diastereoselectivity of the final phenolic oxidation reaction leading to aculeatins.     

Polysubstituted triphenylenes with active groups. Molecular parameters, synthesis, structure, and mesomorphism

Molecular parameters of hexaalkoxytriphenylenes with different substituents on the periphery of the triphenylene nucleus of known and hypothetical structures are calculated. The probability of a discophase for compounds of this series is estimated from molecular parameters. Several compounds of this series having polar groups (NO₂, NH₂) in the 1 position of the triphenylene nucleus have been synthesized. The compounds synthesized were investigated by thermopolarizing microscopy and X-ray diffraction analysis. The data on the mesomorphism of the new compounds are in good agreement with our prediction that alkoxytriphenylenes with polar groups have a discophase. It is established that introduction of an electron-accepting group at position 1 of the triphenylene nucleus expands the temperature range of existence of the discophase to room temperature. On the contrary, introduction of an electron-donating group narrows this interval. Compounds of this series presumably have a hexagonal columnar structure. Ivanovo State University. Warsaw University. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 3, pp. 464–472, May–June, 1998. This work was supported by RFFR grant No. 96-02-19036.     

Existing and emerging strategies for the synthesis of nanoscale heterostructures

Development of new multifunctional nanostructures relies on the ability to make new materials at the nanoscale with control over size, shape and composition. While this control is extremely important to tune several properties, an alternative strategy is to create active interfaces between two or more nanostructures to form nanoscale heterostructures. In these heterostructures, the interfaces play a key role in stabilizing and enhancing the efficiency of the individual components for various applications. In this article, we discuss synthesis methods of different types of nanoscale heterostructures and the role of interfaces in various applications. We present the current state-of-the-art in designing heterostructures and possible upcoming synthetic strategies with their advantages and disadvantages. We present how such heterostructures are highly efficient for catalytic, photovoltaic and nanoelectronic applications drawing several examples from our own studies and from the literature.     

Multicomponent assembly strategies for the synthesis of diverse tetrahydroisoquinoline scaffolds

Several novel multicomponent assembly processes have been developed for the rapid and efficient assembly of various heterocyclic scaffolds bearing a tetrahydroisoquinoline core, each of which allows for facile derivatization to access a diverse array of compounds. This work led to the serendipitous discovery of a new method for the synthesis of a fused quinazolone ring system, which was applied to a one-step total synthesis of the quinazolinocarboline alkaloid rutaecarpine.     

Click chemistry strategies for the accelerated synthesis of functional macromolecules

Click chemistry is one of the most powerful strategies for constructing polymeric soft materials with precise control over architecture and functionality. In this review, we provide a comprehensive summary of the state-of-the art for synthesizing functional polymers and their expanding range of applications. The synthetic and mechanistic aspects are discussed for key reactions that fulfill “click” requirements and their applications in construction of macromolecules with linear, branched, and other complex architectures are described.     

Organometallic based strategies for metal nanocrystal synthesis

Organometallic strategies normally employed for the production of semiconductor quantum dots have been successfully applied to the synthesis of metal nanoparticles. By controlling parameters such as capping agents, reaction temperature and precursor chemistry, precise nanostructures can be obtained that exhibit highly desirable magnetic, optical and catalytic properties.     

Uncatalyzed zirconium-mediated biphenylation of o-dihalobenzenes to form triphenylenes

The reaction of [Zr(biphe)3][(Li.(THF)4)2], where biphe is 2,2'-biphenyldiyl, with an o-dihaloarene produces a triphenylene. Two new bonds are created in this rare example of an uncatalyzed, Zr-mediated aryl-aryl bond formation. Multiple biphe fragments can be incorporated to give larger triphenylene-containing polycyclic aromatic hydrocarbons. This reaction can introduce significant strain and was demonstrated to tolerate alkyl and methoxy substituents.     

Unsymmetrical alkoxy-substituted triphenylenes: the dependence of mesomorphism on molecular shape

Several series of unsymmetrical hexa-alkoxytriphenylenes have been prepared. For almost every series a maximum in the Colh-I clearing point is found for the most symmetrical triphenylene, i.e. when all six alkoxy chains are of equal length. A similar trend is found for the melting points (Tm), although the effect is not so pronounced. A minimum length is required for formation of a columnar mesophase (Col hd). After this critical value has been reached for short alkoxy chains, much lower Colh-I temperatures are then observed for longer chains. Ordered hexagonal columnar phases required for efficient photoluminescence and electroluminescence have been found for several asymmetrical homologues with comparable TCol-I to those observed for the symmetrical homologues, but also with lower Tm. This may facilitate the preparation of mixtures of triphenylenes with the desired ordered hexagonal columnar phases with a TCol-I and a Tm below room temperature.     

One-pot strategies for the synthesis of the tetrasaccharide linkage region of proteoglycans

A linker-attached tetrasaccharide corresponding to the linkage region of proteoglycans was synthesized via one-pot procedures from the silylated monosaccharide derivatives. Regioselective one-pot protection protocols were applied in generating the requisite monosaccharide building blocks whereas stereoselective one-pot glycosylation approaches were utilized to assemble the tetrasaccharide skeleton.     

Convergent strategies for the total synthesis of polycyclic ether marine metabolites

Marine polycyclic ether natural products continue to fascinate chemists and biologists due to their exceptionally large and complex molecular architectures and potent and diverse biological activities. Tremendous progress has been made over the past decade toward the total synthesis of marine polycyclic ether natural products. In this area, a convergent strategy for assembling small fragments into an entire molecule always plays a key role in successful total synthesis. This review describes our efforts to develop convergent strategies for the synthesis of polycyclic ethers and their application to the total synthesis of gambierol, gymnocin-A, and brevenal, and to the partial synthesis of the central part of ciguatoxins and the nonacyclic polyether skeleton of gambieric acids.     

New strategies for the synthesis of N-alkylated indoles (Review)

New data, mostly published in the last five years, on methods for the synthesis of N-alkylated indoles both as a result of direct introduction of the alkyl substituent at the nitrogen atom and by construction of the indole heterocyclic system are reviewed. Only examples of indole derivatives containing branched, sterically hindered, and chiral alkyl substituents at the nitrogen atom are discussed.     

Molecular properties and stacking of 1-substituted hexaalkoxy triphenylenes

In this work we consider the stability of columnar liquid crystals formed by discotic molecules differing only in one core substituent. In particular we concentrate on the 1-substituted 2, 3, 6, 7, 10, 11 hexaalkyloxy triphenylene family, and more specifically on the methoxy derivatives, studying the effects of seven α-substituents (H, Br, CH₃, Cl, F, NH₂, NO₂) on the shape and electronic properties, calculated at density functional level, and relating them with the phase behaviour of the corresponding hexyloxy derivatives. In a second step, we use the optimized structures and the atomic charges in a simplified Monte Carlo simulation of systems of molecules arranged in a columnar fashion, to try to shed light on the consequences of functionalization on the stacking behaviour.     

Synthesis of functionalized triphenylenes and dibenzopyrenes Precursor molecules for polymeric discotic liquid crystals

Discotic liquid crystals represent a promising class of new materials, for example, with respect to their photoconductivity properties. To tailor the processability and mesophase behaviour of such materials, specifically functionalized cores are required as precursor molecules for discotic oligomers, polymers and networks. The paper presents a simple synthetic strategy leading to unsymmetrically functionalized triphenylene and dibenzopyrene derivatives. Furthermore new symmetrical discotic octa-alkoxy-substituted dibenzopyrenes have been synthesized applying this route.     

New Heck coupling strategies for the synthesis of paullone and dimethyl paullone

The short total synthesis of paullone (1) and dimethyl paullone (2) via a novel palladium-catalyzed intramolecular coupling using the o-bromo- and o-iodo anilides of indoles (3 and 3a) and N-methyl indole 4 is described.     

Scalable strategies for the synthesis of well-defined copper metal and oxide nanocrystals

This tutorial review highlights the most promising methods for the preparation of well-defined copper metal and oxide nanocrystals. These methodologies could be applied to other metals. We present the main synthetic strategies and associated mechanisms to control monodispersity, size, morphology and structure of metal and oxide nanomaterials which can adopt spherical, polyhedral, cubic, rod, wire, plate shapes and possibly hollow structures. We also consider the scale-up of the production of these nanocrystals, which is crucial for a wide range of potential applications such as catalysis, photovoltaics, electronics, optics and electrocatalysis.     

Tactics and strategies for the synthesis of iminosugar C-glycosides: a review

Three decades after their first synthesis, iminosugar C-glycosides have become an important class of iminosugars with promising biological and therapeutic properties. The purpose of this review is to provide an overview of the versatile strategies that have been developed to synthesize this family of stable imino-analogues of glycosides and glycoconjugates. Some guidelines and predictive stereoselective models are presented to facilitate the design of synthetic strategies toward iminosugar C-glycosides of defined configuration.