Iron-Catalyzed Cycloaddition of Amides and 2,3-Diaryl-2H-azirines To Access Oxazoles via C-N Bond Cleavage.

A novel and efficient iron-catalyzed cycloaddition reaction using readily available 2,3-diaryl-2H-azirines and primary amides is reported. A wide range of trisubstituted oxazoles could be achieved in good yields with good functional group compatibility. In this transformation, two C-N bonds were cleaed and new C-N and C-O bonds were formed.

Brønsted-Acid-Catalyzed Synthesis of 3-Alkoxy and 3-Sulfamido Indanones via a Tandem Cyclization.

Brønsted-acid-catalyzed allylic substitution reactions of the in situ generated 3-hydroxy indanones with alcohols and sulfamides were investigated, which provided a facile route for the synthesis of a large variety of 3-alkoxy and 3-sulfamido indanones. The key intermediates, 3-hydroxy indanones, were obtained through the intramolecular Meyer-Schuster rearrangement of o-propargyl alcohol benzaldehydes. The resulting 3-benzyloxy indanone could be selectively modified by allylic sulfonamidation and reduction reactions.

Monodisperse Bismuth-Halide Double Perovskite Nanocrystals Confined in Mesoporous Silica Templates.

Metal halide perovskites have fascinating electronic properties and have already been implemented in various devices. Although the behavior of the properties of lead halide perovskite nanocrystals has been studied, the properties of lead-free perovskite nanocrystals are less well-understood because synthesizing them is still very challenging. Here, a simple and popularizable method has been demonstrated to grow monodisperse bismuth-halide double perovskite nanocrystals, Cs2AgBiBr6 (1), inside three kinds of mesoporous silica templates. The size and morphology of nanocrystals depend on the structure and pore size of the template. Structural analysis shows that the nanocrystals of various sizes and morphologies retain the crystal structure of bimetallic perovskite. 1 exhibits different morphologies in the silicon channels of three templates: square nanoparticles in KIT-6, spherical and rodlike particles in SBA-15, and nanowires in MCM-41. UV-vis-NIR and photoluminescence measurements show us the variation of band gap and carrier recombination time due to quantum confinement of nanocrystals in mesoporous silicon materials. The band gaps of nanocrystals in the template exhibit an obvious blue shift compared with that of the bulk sample, and the carrier recombination time is significantly shortened. We show that mesoporous silicon templates can be used to prepare lead-free perovskite nanocrystals, and the controllable preparation of nanocrystals can be achieved by the template's own characteristics. This provides a new idea for us to find new functional materials of lead-free metal halide solid-state light-emitting diodes.

Crystal and Band-Gap Engineering of One-Dimensional Antimony/Bismuth-Based Organic-Inorganic Hybrids.

Hybrid halide perovskites are emerging semiconducting materials with a diverse set of remarkable optoelectronic properties. Besides the widely studied lead halide perovskites, Pb-free metal halides such as Bi- and Sb-containing hybrid organic-inorganic materials have shown potential as semiconductors and have been deemed candidates for optoelectronic devices. Here, we report a series of 1D Sb/Bi-based organic-inorganic hybrid alloys: [4ApyH]SbxBi1-xIyBr4-y, where 4ApyH stands for the 4-aminopyridine cations. These compounds are assembled by edge-sharing octahedral [MX6] units stabilizing 1D chains with organic cations filled in between. The crystallographic data of eight selected complexes show that [4ApyH]SbxBi1-xIyBr4-y has at least five phases (space group) with the difference metal and halogen content: Pbca ([4ApyH]BiI4), Pca21 ([4ApyH]Sb0.5Bi0.5I4), P21/c ([4ApyH]SbI4 (100 K), [4ApyH]BiI2Br2, [4ApyH]BiBr4, and [4ApyH]SbBr4 (100 K)), I2/a ([4ApyH]Sb0.5Bi0.5I2Br2and [4ApyH]SbI2Br2), and C2/c ([4ApyH]SbI4 (298 K) and [4ApyH]SbBr4 (298 K)). Powder X-ray diffraction shows that the phase of the sample changes with a change of the metal and halogen ratios, and the change law accords with Vegard's law. The optical band gaps are heavily affected by the metal and halide contents, ranging from 1.94 eV for [4ApyH]BiI4 to 2.73 eV for [4ApyH]SbBr4. When Sb substitutes for Bi to form an alloy, the band gap increases from 1.94 for [4ApyH]BiI4 to 1.67 eV for [4ApyH]SbI4, from 2.13 eV for [4ApyH]BiI2Br2 to 2.41 eV for [4ApyH]SbI2Br2, and from 2.55 eV for [4ApyH]BiBr4 to 2.73 eV for [4ApyH]SbBr4. The conductivity of [4ApyH]SbxBi1-xI4 increased from ∼1.00 × 10-15 to 2.14 × 10-8 S cm-1 with an increase of the Sb content. Solution-deposited thin films of the nine complexes show the same (110) orientation, displaying a parallel growth orientation with respect to the substrate. The devices of [4ApyH]Sb0.8Bi0.2I4 and [4ApyH]SbI4 demonstrated stable open-circuit photovoltages of 0.55 and 0.44 V, steady-state short-circuit photocurrent densities of 1.52 and 1.81 mA cm-2, and light-to-electrical energy conversion efficiencies of 0.29% and 0.30%, respectively.

Modular 2,3-diaryl-2H-azirine synthesis from ketoxime acetates via Cs2CO3-mediated cyclization.

A modular 2H-azirine synthesis from ketoxime acetates via Cs2CO3-mediated cyclization has been developed. The reaction utilizes easily available starting materials and provides a general synthetic route to 2,3-diaryl-2H-azirines in good to excellent yields under mild conditions, which is complementary to the conventional approaches for the synthesis of 2H-azirines. A gram-scale reaction was performed to demonstrate the scale-up applicability of this synthetic method. Importantly, 2H-azirines can be efficiently converted to various azaheterocycles.

Recent developments in the group-1B-metal-catalyzed synthesis of pyrroles.

Pyrroles are important synthetic targets as a result of their occurrence in numerous biologically active molecules, their important roles in diverse living processes, and their utility as versatile intermediates. As a consequence, numerous efforts focused on the development of concise and efficient methods for the construction of pyrroles. Compared with other transition metals, the group 1B metals (Cu, Ag and Au) are probably more versatile and widely used for the synthesis of pyrroles in organic chemistry. Considering the importance of both topics in organic synthesis, here we summarize recent achievements in the synthesis of pyrroles catalyzed by monometallic systems which belong to the group 1B metals (Cu, Ag and Au).

N'-(5-Bromo-2-hy-droxy-benzyl-idene)-4-methyl-benzohydrazide.

The mol-ecule of the title compound, C(15)H(13)BrN(2)O(2), displays an E conformation with respect to the C=N double bond and the dihedral angle between the planes of the benzene rings is 3.1 (2)°. An intra-molecular O-H⋯N inter-action generates an S(6) ring. In the crystal, mol-ecules are linked by N-H⋯O hydrogen bonds, forming C(4) chains along the c-axis direction.

Enantioselective recognition of chiral acids by supramolecular interactions with chiral AIEgens.

Novel chiral AIEgens bearing optically pure amino groups were synthesized and showed excellent discrimination for a series of chiral acidic compounds and amino acids. Interestingly, after supramolecular assembly with 4-sulfocalix[4]arene, the obtained complexes showed enhanced enantioselectivity for chiral acids.

N'-(5-Hydr-oxy-2-nitro-benzyl-idene)-2-methoxy-benzohydrazide.

The asymmetric unit of the title compound, C(15)H(13)N(3)O(5), contains two independent mol-ecules. Each mol-ecule displays an E configuration with respect to its C=N double bond. The dihedral angles between the two benzene rings are 11.1 (2) and 10.9 (2)° in the two mol-ecules. In the crystal structure, mol-ecules are linked through inter-molecular O-H⋯O hydrogen bonds, forming chains running along the a axis.

3-Hydr-oxy-N'-(5-hydr-oxy-2-nitro-benzyl-idene)-2-naphthohydrazide.

The mol-ecule of the title compound, C(18)H(13)N(3)O(5), displays an E configuration with respect to the C=N double bond. The dihedral angle between the benzene ring and the naphthyl system is 1.1 (2)°. In the crystal structure, mol-ecules are linked through inter-molecular N-H⋯O and O-H⋯O hydrogen bonds, forming a three-dimensional network.

Tracking the dimensional conversion process of semiconducting lead bromide perovskites by mass spectroscopy, powder X-ray diffraction, microcalorimetry and crystallography.

The structural information of a material in both the solid state and solution state is essential to the in-depth understanding of the properties of inorganic-organic hybrid materials. A one-dimensional (1D) lead bromide formulated as [H][NH3(CH2)2SS(CH2)2NH3][H2O][PbBr5] (1) could be converted into a new two-dimensional (2D) complex, [NH3(CH2)2SS(CH2)2NH3][PbBr4] (2), by soaking the crystals in water. The isolated 2D compound showed single-layer lead-halide perovskite structures. Electrospray ionization mass spectrometry (ESI-MS) analyses of the reaction solution revealed that the [PbBr3]- fragments are initially formed from the rapid decomposition of the 1D [PbBr5]3- chains and subsequently reassemble into 2D [PbBr4]2- layers, which was verified by powder X-ray diffraction (PXRD) and microcalorimetry. Because of the decomposition and reassembly process, complex 1 could be used as a precursor to synthesize M2+-doped 2D lead bromide perovskites, namely, Mn@2, Ni@2 and Cd@2. In addition, preliminary tests indicated that complex 2 exhibited a lower optical band gap (3.25 eV) and higher electrical conductivity (3.2 × 10-11 S cm-1) than complex 1 (3.38 eV, 5.4 × 10-12 S cm-1).

4-Chloro-N'-(5-chloro-2-hydroxy-benzyl-idene)benzohydrazide.

The mol-ecule of the title compound, C(14)H(10)Cl(2)N(2)O(2), displays a trans configuration with respect to the C=N double bond and has an intramolecular O-H⋯N hydrogen bond. The dihedral angle between the two benzene rings is 1.4 (2)°. In the crystal structure, mol-ecules are linked through inter-molecular N-H⋯O hydrogen bonds, forming chains running along the a direction.

4-Chloro-N'-(2-hydr-oxy-1-naphthyl-idene)benzohydrazide.

The mol-ecule of the title compound, C(18)H(13)ClN(2)O(2), displays a trans configuration with respect to the C=N double bond. The dihedral angle between the benzene and naphthyl ring systems is 6.0 (2)°. An O-H⋯N hydrogen bond is observed in the mol-ecular structure. In the crystal structure, mol-ecules are linked through inter-molecular N-H⋯O hydrogen bonds and π-π stacking inter-actions [centroid-centroid distance = 3.603 (2) Å], forming chains running along the b axis.

(E)-4-Chloro-N'-(4-hydroxy-benzyl-idene)-benzohydrazide.

The mol-ecule of the title compound, C(14)H(11)ClN(2)O(2), displays a trans configuration with respect to the C=N double bond. The dihedral angle between the two benzene rings is 12.8 (3)°. In the crystal structure, mol-ecules are linked through inter-molecular O-H⋯O and N-H⋯O hydrogen bonds and C-H⋯π inter-actions, forming a three-dimensional network.

(E)-4-Chloro-N'-[1-(4-hydroxy-phenyl)-ethylidene]benzohydrazide.

The mol-ecule of the title compound, C(15)H(13)ClN(2)O(2), displays a trans configuration with respect to the C=N double bond. The dihedral angle between the two benzene rings is 15.1 (3)°. A strong intra-molecular O-H⋯N hydrogen bond is observed. In the crystal structure, mol-ecules are linked through inter-molecular N-H⋯O hydrogen bonds, forming chains running along [101].

Iron-Catalyzed Radical Cycloaddition of 2H-Azirines and Enamides for the Synthesis of Pyrroles.

A novel and efficient Fe-catalyzed radical cycloaddition of 2H-azirines and enamides for the synthesis of substituted pyrroles has been developed. The radical cycloaddition reaction proceeded through a conceptually new Fe(II)-catalyzed homolytic cleavage of C-N bond of 2H-azirines sequential radical cyclization with enamides. The reaction used readily available starting materials, tolerated various functional groups, and afforded valuable triaryl-substituted pyrroles in good to high yields under mild reaction conditions.

K2S2O8/TEMPO-Induced Cascade Oxidative Cyclization/1,2-Migration of Electron-Deficient Groups: Strategy for the Construction of 1 H-Pyrrol-2(3 H)-ones.

A K2S2O8/TEMPO-induced oxidative cyclization of N-unprotected enaminoesters and enaminones that gave 1 H-pyrrol-2(3 H)-ones in good yields with broad functional group compatibility is reported. This method provides easy access to 1,2-carbon migration of ester or acyl group under transition-metal-free conditions.

KI-catalyzed oxidative cyclization of α-keto acids and 2-hydrazinopyridines: efficient one-pot synthesis of 1,2,4-triazolo[4,3-a]pyridines.

A one-pot approach to substituted 1,2,4-triazolo[4,3-a]pyridines has been developed that is based on a KI-catalyzed oxidative cyclization of α-keto acids and 2-hydrazinopyridines. This transition-metal-free procedure was highly efficient and shows good economical and environmental advantages.

Copper-Catalyzed Oxidative Cyclization/1,2-Amino Migration Cascade Reaction.

A novel and efficient copper-catalyzed tandem oxidative cyclization/1,2-amino migration of readily available enamino esters for the synthesis of substituted pyrroles has been developed. In this reaction, one C-N bond was cleaved, and two new C-N bonds and one C(sp2)-C(sp2) bond were constructed in one pot. This catalytic system has the obvious advantages of mild reaction conditions and the use of oxygen as the oxidant. The reaction tolerates a wide range of functional groups and is a reliable method for the straightforward synthesis of valuable aminomethyl-substituted pyrroles in good yields.

[Determination of fraxinellone in root bark of Dictamnus dasycarpus by RP-HPLC].

OBJECTIVE: To develop a RP-HPLC method for determination of fraxinellone in Dictamnus dasycarpus. METHOD: RP-HPLC conditions were as follows: AT-LICHROM C18(4.6 mm x 250 mm) column, MeOH-H2O (70:30) as a mobile phase, detection wavelength 240 nm, column temperature 25 degrees C, Flow velocity 0.5 mL x min(-1). RESULT: Linear relationship is very good (r = 0.9999) in 0.018-0.18 mg x mL(-1). The average recovery is 98.9%, RSD is 1.2% (n = 4). CONCLUSION: The method is simple and repeatable and can be used for quantitative analysis of fraxinellone in root bark of D. dasycarpus.