Bi-Qin Wang

Application of Asymmetric Ylide Cyclopropanation in the Total Synthesis of Halicholactone

Halicholactone belongs to a family of oxylipins that have important and interesting biological activities, such as inhibiting lipoxygenase and farnesyl protein transferase. These compounds are featured unique molecular structures containing a 1,2-trans-substituted cyclopropane subunit with a 6-, 8or 9-membered lactone (Figure 1). The first total synthesis of halicholactone 1 was accomplished by Wills et al. using (S)-malic acid as the starting material. In their synthesis, the cyclopropane fragment was obtained by the reaction of the unsaturated ester with Corey ylide; the lactone unit was constructed by Yamaguchi s mixed anhydride method. Later, Takemoto, Tanaka, and their co-workers reported an asymmetric total synthesis of halicholactone 1 from chiral [(diene)Fe(CO)3], in which the cyclopropane fragment was prepared in moderate yields with excellent diastereoselectivity by the modified Simmons–Smith reaction of a chiral allylic alcohol. Kitahara documented a total synthesis of halicholactone by using (1S,5S,6R)-5hydroxybicycloACHTUNGTRENNUNG[4.1.0]-heptan-2-one as a chiral building block. Datta s group described a 12-step synthesis of compound 29 by employing the cyclopropanation of trans-cinnamyl alcohol through Charette s protocol, finishing the formal synthesis of halicholactone. Mohapatra et al. also reported the total synthesis of halicholactone with (R)-2,3-Oisopropylidene glyceraldehyde as a chiral pool building block. In our studies on ylide chemistry in organic synthesis, we developed an efficient method for the preparation of vinylcyclopropanes from a readily available d-camphorderived ylide. In this cyclopropanation, excellent diastereoselectivity (cis/trans) and enantioselectivity can be achieved. Very recently, we found that this cyclopropanation could be applied successfully to the preparation of intermediate 13 in five steps to provide a formal synthesis of halicholactone. In this communication, we wish to report our results as well as the total synthesis of halicholactone in detail.

Tetraphenylethene–triphenylene oligomers with an aggregation-induced emission effect and discotic columnar mesophase

Tetraphenylethene derivatives not only exhibit “aggregation-induced emission” (AIE) effects, but also can form a mesophase with a turbine-like rigid core. Here we report the synthesis of three tetraphenylethene–triphenylene oligomers 7, 8E and 8Z by a CuSO4/sodium ascorbate catalyzed alkyne–azide cycloaddition reaction (CuAAC), and the successful separation of the cis- and trans-isomers by column chromatography. The structure and conformation of the oligomers were fully characterized. The photophysical properties were studied by using UV-vision and photoluminescent (PL) spectroscopy. The morphology of the aggregates was investigated by scanning electron microscopy (SEM), and the thermal stability and mesomorphic properties were investigated using thermal gravimetric analysis (TGA), polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). The results revealed that the oligomers possess an AIE effect, but display no mesomorphism. However, 7 exhibits a hexagonal columnar mesophase when mixed with 2,4,7-trinitrofluorenone (TNF), forming a charge transfer complex.

Direct Oxidative Arylation of Aryl CH Bonds with Aryl Boronic Acids via Pd Catalysis Directed by the N,N‐Dimethylaminomethyl Group

Biaryl skeletons were directly constructed via palladium-catalyzed ortho-arylation of N,N-dimethyl benzylamine with aryl boronic acids with high efficiency and high regioselectivity under open-flask conditions. The N,N-dimethylaminomethyl group was first applied as a directing group in such an oxidative coupling. Various substrates proved to be efficient coupling partners, furnishing the corresponding ortho-monoarylated or -diarylated arenes in moderate to good yields under mild conditions.

Truxene discotic liquid crystals with two different ring substituents: synthesis, mesomorphism and high charged carrier mobility

Discotic liquid crystals as a kind of promising organic electronic materials show self-assembly property as well as high charged carrier mobility. New truxene discogens, six 3,8,13-tri(alkoxy)-2,7,12-tri(methoxy)truxenes and two 3,8,13-tri(alkoxy)-2,7,12-tri(hydroxy)truxenes, have been synthesised with improved yields, were fully characterised and exhibited good thermal stability. The mesomorphism has been investigated by using polarised optical microscopy, differential scanning calorimetry and X-ray diffraction, and they exhibited ordered hexagonal columnar mesophase. More importantly, the charge carrier mobilities of 6d and 7f have been measured by using time-of-flight technique and 7f displayed hole drift mobility rate of 4.2 × 10−2 cm2 V−1 s−1 in the Colho phase and 0.1 cm2 V−1 s−1 at a lower temperature M mesophase.

Triphenylene discotic liquid crystal trimers synthesized by Co2(CO)8-catalyzed terminal alkyne [2 + 2 + 2] cycloaddition

Summary The synthesis of star-shaped discotic liquid crystal trimers using Co2(CO)8-catalyzed terminal alkyne [2 + 2 + 2] cycloaddition reaction is reported. The trimers consist of three triphenylene discotic units linked to a central 1,2,4-trisubstituted benzene ring via flexible spacers. The trimers were synthesized in the yields up to 70% by mixing the monomers with 10 mol % of Co2(CO)8 as the catalyst in refluxing 1,4-dioxane. The liquid crystalline properties were investigated by using polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Trimer 4 with an ester connecting group and a longer spacer exhibited a rectangular columnar mesophase, while 5b and 5c possessing an ether linkage and a shorter spacer display a hexagonal columnar mesophase. The connecting functional group and the length of the flexible spacer between the central benzene ring and the triphenylene units have pivotal influence on the mesomorphism.

The influence of alkyl chain substitution pattern on the two- and three-dimensional self-assembly of truxenone discogens

The synthesis of new discotic liquid crystals and the study of self-assembly behaviours are important for the supramolecular chemistry and organic electronics. Six new truxenone discogens 7a–f with different alkyl chain substitution patterns were synthesised and all exhibited only one three-dimensional ordered hexagonal columnar mesophase with wide temperature ranges including room temperature, which were characterised with polarising optical microscopy, differential scanning calorimetry and X-ray diffraction. The self-assembly behaviours in solutions were studied by using concentration-variation 1H NMR and scanning electron microscopy. The two-dimensional ordered self-assembly of 7c and 7f on the liquid–solid interface of highly oriented pyrolytical graphite were imaged by scanning tunnelling microscopy, and the results showed that the two-dimensional monolayer self-assembled structures on the atomically flat surfaces can be controlled by the peripheral alkyl chain substitution patterns.

Synthesis of naphthalene derivatives through inexpensive BF 3 ·Et 2 O-catalyzed annulation reaction of arylacetaldehydes with arylalkynes

An inexpensive BF3·Et2O-catalyzed annulation reaction of arylacetaldehydes with arylalkynes has been developed. Various substituted phenylacetaldehydes and phenylacetylenes can undergo this reaction, producing corresponding α-aryl substituted naphthalene derivatives. Use of inexpensive and readily available BF3·Et2O catalyst constitutes the most attractive advantage of this transformation.

Synthesis and characterisation of 3-armed dendritic molecules with triphenylbenzene or triphenyltriazine as core and triphenylene derivative as shells

Two series 3-armed dendritic molecules with their 1,3,5-tris(4-methyloxyphenyl) benzene or 2,4,6-tris(4- hydroxylphenyl)-1,3,5-s-triazine core and triphenylene derivative shells connected by soft hydrocarbon chains have been synthesised and fully characterised. Whether liquid crystal (LC) or photoluminescence materials have been tuned by changing the length of the soft chain and they have been studied by POM, DSC, XRD, UV-Vis and PL. The results show that all the new dendritic compounds display UV to blue fluorescence in solvents such as DCM, THF and acetone. The TC3 compound bearing 1,3,5-tris(4-hydroxylphenyl) benzene core exhibits LC property with rectangular columnar phase (Colr) on cooling.

Monosubstituted ferrocene liquid crystals containing click triazole with a wide nematic phase temperature range

ABSTRACT New monosubstituted ferrocenomesogens of the 1,4-substituted-1,2,3-triazole series 3a-3d and the 5-halogen-1,4-substituted-1,2,3-triazole series 4a-4d were successfully synthesised through a facile and versatile synthetic route using click reactions with moderate yields, in different atmospheres, and catalysed by different amounts of CuX (X = Br, I). Two series of compounds exhibited a typical nematic liquid crystal texture, and the 5-halogen-1,4-substituted-1,2,3-triazole series 4 had a wider mesomorphic temperature range than the corresponding series 3 due to the effect of the halogen atom substituent on the triazole. These compounds showed similar absorption spectra, but the fluorescence emission spectra of 4 were obviously redshift relative to 3. Cyclic voltammetry investigations revealed that the redox-active ferrocenyl groups of 3 and 4 follow one-electron transfer processes. GRAPHICAL ABSTRACT

Influence of peripheral alkyl chain length on the mesomorphic behaviours of hexasubstituted triphenylene 2,3-dicarboxylic esters

ABSTRACT A comparative study of our established synthetic approaches to hexasubsituted triphenylenes 2,3-dicarboxylic esters containing four identical β-alkoxy and two adjacent β-alkoxycarbonyl side chains shows that the phase behaviours of small-sized discotic liquid crystals can be tailored over a wide range by simply varying the length of the peripheral alkyl chains. All the prepared esters in two series were observed to form a single hexagonal columnar phase, except for Tp4-1 having four β-butyloxy and two adjacent β-methoxycarbonyl chains which displays two columnar mesophase behaviours with a transition from the columnar plastic phase to hexagonal columnar phase. A significant difference between the two mesophase was observed in the variable temperature X-ray diffraction studies, and the mesophase assignment was also confirmed by polarising optical microscopy and differential scanning calorimetry. Moreover, the prepared esters in each series display the general trend of decreasing clearing temperature upon increasing alkoxy or alkoxycarbonyl chains length. The intermediate triphenylene 2,3-dicarboxylic acids were also found not only to exhibit columnar hexagonal mesophase over a narrower temperature range by maintaining high melting and clearing points but also to form organogel on mixing with toluene or dichloromethane with the assistance of hydrogen bonding. GRAPHICAL ABSTRACT