Wenxia Gao

Unexpected Copper-Catalyzed Cascade Synthesis of Quinazoline Derivatives

The first example of a copper-catalyzed cascade reaction of (2-aminophenyl)methanols with aldehydes using the combination of cerium nitrate hexahydrate and ammonium chloride has been developed, leading to a wide range of 2-substituted quinazolines in moderate to excellent yields. The efficiency of this transformation was demonstrated by compatibility with a wide range of functional groups. Thus, the method represents a convenient and practical strategy for synthesis of 2-substituted quinazoline derivatives.

Copper-Catalyzed Three-Component Reaction for Regioselective Aryl- and Heteroarylselenation of Indoles using Selenium Powder

A new and efficient copper-catalyzed C3 aryl- and heteroarylselenation of indoles employing selenium powder has been developed. The advantages of this chemistry involve the use of cheap selenating reagents, tolerance of a variety of functional groups, and practicality. In addition, this protocol has been further elaborated in an intramolecular phenylselenation of a (hetero) aryl C-H bond to construct an important motif of benzoselenopheno[3,2-b]indole. A preliminary mechanism study suggests that the reaction starts with a Ullman-type selenation between aryl iodides and selenium, followed by an oxidative cross-coupling with indole. The utility of this method has been demonstrated in an efficient gram-scale synthesis and an application to the synthesis of tubulin polymerization inhibitor.

Palladium-catalyzed decarboxylative coupling of isatoic anhydrides with arylboronic acids.

The decarboxylative coupling of isatoic anhydrides with arylboronic acids was realized for the first time in the presence of Pd(2)(dba)(3) and DPEphos, achieving aryl o-aminobenzoates with yields ranging from moderate to good. The efficiency of this procedure was demonstrated by good compatibility with fluoro, chloro, bromo, nitro, cyano, trifluoromethyl, formacyl, acetyl, thienyl, and naphthyl groups. Preliminary mechanistic experiments using deuterium labeling showed that the oxygen atom was derived from dioxygen.

Indene-1,3-dionemethylene-4H-pyran derivatives containing alkoxy chains of various lengths: aggregation-induced emission enhancement, mechanofluorochromic properties and solvent-induced emission changes

A series of D–π–A indene-1,3-dionemethylene-4H-pyran (IDMP) derivatives with aggregation-induced emission enhancement phenomena were synthesized using indene-1,3-dionemethylene as an electron acceptor and a phenyl ring containing different lengths of alkoxy chains as an electron donor. The as-synthesized IDMP solids emit from red to yellow fluorescence and the fluorescence emissions show obvious blue shifts with the increase of the length of the alkoxy chains. Some of these compounds exhibit obvious redshift mechanofluorochromic (MFC) properties, and the longer the alkoxy chain, the more remarkable the MFC properties. Moreover, the fluorescence emission of these compounds can be switched by using various external stimuli such as grinding, annealing, and solvent fuming. In particular, solvent-induced emission changes similar to those resulting from MFC properties can be achieved by a simple dissolution–desolvation process in different solvent systems, such as chloroform and THF. X-ray diffraction experiments reveal that the MFC properties and solvent-induced emission changes can both be considered as altered-morphology-induced emission properties, which are ascribed to the transformation between the crystalline and amorphous states. The results indicate that the subtle manipulation of the length of the alkoxy chain of IDMP derivatives could endow them with unique and tunable solid-state optical properties.

Highly sensitive conjugated polymer fluorescent sensors based on benzochalcogendiazole for nickel ions in real-time detection

Reports about fluorescent sensors for the highly sensitive and selective detection of Ni2+ are rare compared with Hg2+, Ag+, Cd2+, Pb2+, Cr3+, etc. Herein, we report the synthesis and application of two conjugated polymer fluorescent sensors, P-1 and P-2, using benzochalcogendiazole and triazole as cooperative receptors of Ni2+. The synthesis was carried out by the polymerization of 4,7-diethynylbenzoselenadiazole (M-2) and 4,7-diethynylbenzothiadiazole (M-3) with 2,7-diazido-9,9-dioctyl-9H-fluorene (M-1)via copper-catalyzed azide–alkyne cycloaddition. P-1 and P-2 exhibit emission peaks at 535 nm and 514 nm, and show yellow and green fluorescence, respectively. These two polymers showed outstanding fluorescence response behavior toward Ni2+ during real-time detection. Compared with benzothiadiazole-based P-2, benzoselenadiazole-based P-1 showed higher sensitivity and selectivity, and its detection limit could reach 2.4 nM, which might be due to the specific electronegativity of selenium. This work increases the application scope of the click reaction in regard to the design and synthesis of novel conjugated polymer fluorescent sensors based on the benzochalcogendiazole unit.

A Novel Glucose/pH Responsive Low-Molecular-Weight Organogel of Easy Recycling

A new phenylboronic acid based gelator was developed to prepare low-molecular-weight organogel (LMOG), which could interact with several solvents to assemble into a three-dimensional nanofiber network. (1)H NMR spectroscopy study suggests that the driving force for the gelation includes hydrogen bonding and π-π stacking. Evaluated by UV-spectroscopy, the gel showed a prompt initial response to glucose at low concentration of 0.012 mmol/mL, which is a critical concentration of venous plasma glucose for diabetes. Significantly, this organogel exhibits excellent sensitivity to glucose among seven sugars tested (i.e., mannitol, galactose, lactose, maltose, sucrose, and fructose). The proposed formation of hydrogen-bonded complexes during the glucose sensing was supported by our energy calculation. Meanwhile, this organogel exhibits pH-response. Importantly, this LMOG could be conveniently recycled and thus be reused.

Copper-Catalyzed Three-Component Coupling Reaction of Azoles, Se Powder, and Aryl Iodides

A copper-catalyzed three-component coupling reaction of azoles, Se powder, and aryl iodide is described for the first time. This transformation provides a straightforward and facile pathway to synthesis 2-arylselanyl-azoles via a copper-catalyzed double C-Se bonds formation process. This reaction is attractive and practical since the cheap copper catalyst is employed and it does not require ligands, proceeds in generally good yields, and has a broad range of functional groups tolerance.

The effect of N-alkyl chain length on the photophysical properties of indene-1,3-dionemethylene-1,4-dihydropyridine derivatives

A series of donor–π–acceptor indene-1,3-dionemethylene-1,4-dihydropyridine (IDM-DHP) derivatives with different alkyl chain lengths on the DHP ring were synthesized to investigate the effect of N-alkyl chains on their fluorescence properties in the aggregated state. These compounds with highly distorted conformations show obvious aggregation-induced emission enhancement phenomena in a THF/water mixture because of the restriction of intramolecular rotation in the aggregated state, as confirmed by solution thickening experiments. The as-synthesized IDM-DHP solids emit strong yellow fluorescence and the general trend of their emission wavelengths decreases with the increase of the N-alkyl chain length. It is found that these compounds exhibit outstanding reversible mechanofluorochromic (MFC) properties, and N-alkyl chains play a functional role in tuning their MFC behaviours, that is, the longer alkyl-containing IDM-DHP solids show larger MFC spectral redshifts, which should be ascribed to the weaker CH/π hydrogen bonds in the molecules and as a result looser molecular stacking, as revealed by the single crystal X-ray diffraction analysis. Additionally, the fluorescence emission of the ground samples of these compounds can recover by annealing or solvent fuming. X-ray diffraction experiments reveal that the transformation between crystalline and amorphous states under various external stimuli should be responsible for the MFC properties. This work demonstrates that a simple alkyl chain change in the skeleton of some organic fluorophores can be used to tune their fluorescence properties in the aggregated state, which provides good design ideas for the development of novel IDM-DHP derivatives with MFC properties.

Copper-Catalyzed Oxirane-Opening Reaction with Aryl Iodides and Se Powder

Using Se powder as the selenating reagent, the copper-catalyzed double C-Se cross-coupling of aryl iodides, epoxides, and elemental selenium has been developed. This strategy provides a straightforward approach to the synthesis of β-hydroxy phenylselenides with excellent regioselectivity of the ring opening reaction. This process proceeds in generally good yields and is compatible with a broad range of functional groups.

Solvent-free synthesis of 3,5-di(hetero)aryl-1,2,4-thiadiazoles by grinding of thioamides under oxidative conditions

An efficient and facile synthesis of 3,5-di(hetero)aryl-1,2,4-thiadiazoles by oxidative dimerisation of thioamides by grinding with NBS under solvent-free conditions at room temperature has been developed. The efficiency of this reaction was demonstrated by the compatibility with trifluoromethyl, methyl, methoxy, chloro, pyridyl and thienyl groups. This method has notable advantages in terms of short reaction times, high yields and is a more practical alternative to the existing methods to access these compounds.