Synthesis and Structure of 1,2-Dimethylene[2.10]metacyclophane and Its Conversion into Chiral [10]Benzenometacyclophanes: Synthesis and Structure of 1,2-Dimethylene[2.10]metacyclophane and Its Conversion into Chiral [10]Benzenometacyclophanes

Bromination of 5,21-di-tert-butyl-8,24-dimethoxy-1,2-dimethyl[2.10]metacyclophan-1-ene (MCP-1-ene; 1) with benzyltrimethylammonium tribromide exclusively afforded 1,2-bis(bromomethyl)-5,21-di-tert-butyl-8,24-dimethoxy[2.10]MCP-1-ene (2). Debromination of 2 with Zn and AcOH in CH₂Cl solution at room temperature for 24 h produced dimethylene[2.10]MCP 7 in 92 % yield, which is a stable solid compound. Compound 7 was treated with dimethyl acetylenedicarboxylate (DMAD) to provide 1,2-(3′,6′-dihydrobenzo)-5,21-di-tert-butyl-8,24-dimethoxy[2.10]MCP-4′,5′-dimethylcarboxylate (8) in good yield. Diels–Alder adduct 8 was converted into a novel and inherently chiral areno-bridged dimethoxy[2.10]MCP-4′,5′-dimethylcarboxylate 9, possessing C₁ symmetry, by aromatization with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). A new type of N-phenyl-maleimide substituted 1,2-(3′,6′-dihydrobenzo)-5,21-di-tert-butyl-8,24-dimethoxy[2.10]MCP-4′,5′-N-phenylmaleimide 10 was also synthesized from 7 through treatment with N-phenylmaleimide in toluene at 110 °C followed by aromatization with DDQ. Single-crystal X-ray analysis of 9 revealed the formation of a syn-isomer

Pyrene-based aggregation-induced emission luminogens and their applications

"Unity is force"-Aesop. It is a common phenomenon that traditional chromophores exhibit high fluorescence in dilute solutions, yet luminescence is quenched at high concentrations or in the aggregate state, i.e. "aggregation-caused quenching" (ACQ). Tang reported the unusual photophysical observation that luminogens can exhibit weak or no fluorescence in solution, yet they are highly emissive in the aggregate or solid state; this is defined as aggregation-induced emission (AIE). The discovery of AIE helped solve the ACQ effect in traditional luminophores. Pyrene is an important polycyclic aromatic hydrocarbon (PAH), which exhibits very different photophysical behavior in solution versus the aggregate state, and the ACQ effect has played a dominant role in pyrene chemistry. The ACQ effect is harmful for some practical applications and is a challenge in organic light-emitting diodes (OLEDs) and light-emitting electrochemical cells, for which the effect is more severe in the solid state. Thus, how to overcome the ACQ effect observed in pyrene chemistry still remains a challenge. In this review, we discuss how following basic AIE mechanisms such as the restriction of intramolecular motion (RIM), excited-state intramolecular proton transfer (ESIPT), and twisted intramolecular charge transfer (TICT), can transform pyrene-based ACQ luminogens to AIE luminogens with excellent optical properties. Furthermore, prospective applications of pyrene-based AIEgens are discussed, as is the potential for designing new organic functional materials

Synthesis and conformational studies of chiral macrocyclic [1.1.1]metacyclophanes containing benzofuran rings

Macrocyclic [1.1.1]metacyclophanes (MCPs) containing benzene and benzofuran rings linked by methylene bridges and which can be viewed as calixarene analogues, have been synthesized by demethylation of [3.3.1]MCP-diones with trimethylsilyl iodide (TMSI) in MeCN. The [3.3.1]MCP-diones are synthesized by using (p-tolylsulfonyl)methyl isocyanide (TosMIC) as the cyclization reagent in N,N-dimethylformamide (DMF) with an excess of sodium hydride. ¹H NMR spectroscopy revealed that the remaining hydroxyl group on the phenyl ring is involved in intramolecular hydrogen bonding with the oxygen of one of the benzofuran rings. O-Methylation at the lower rim of monohydroxy[1.1.1]MCP in the presence of K₂CO₃ in acetone afforded a novel and inherently chiral calixarene analogue, namely the macrocyclic [1.1.1]MCP, possessing C₁ symmetry. The inherent chirality of the two conformers was characterized by ¹H NMR spectroscopy by addition of an excess of Pirkle's chiral shift reagent, which caused a splitting of the corresponding methylene protons to AB patterns. Single crystal X-ray analysis revealed the adoptation of a hemisphere-shaped cone isomer. DFT calculations were carried out to investigate the energy-minimized structures and the hydrogen bonds of the synthesized MCPs

Synthesis and conformations of [2.n]metacyclophan-1-ene epoxides and their conversion to [n.1]metacyclophanes

A series of syn- and anti-[2.n]metacyclophan-1-enes have been prepared in good yields by McMurry cyclizations of 1,n-bis(5-tert-butyl-3-formyl-2-methoxyphenyl)alkanes. Significantly, acid catalyzed rearrangements of [2.n]metacyclophan-1-enes afforded [n.1]metacyclophanes in good yield. The ratios of the products are strongly regulated by the number of methylene bridges present. The percentages of the rearrangement products increase with increasing length of the carbon bridges. Characterization and the conformational studies of these products are described. Single crystal X-ray analysis revealed the adoption of syn- and anti-conformations. DFT calculations were carried out to estimate the energy-minimized structures of the synthesized metacyclophanes

Synthesis, structures and conformational studies of 1,2-dimethyl[2.10]metacyclophane-1-enes

A series of 1,2-dimethyl[2.10]metacyclophan-1-enes (MCP-1-enes) containing different substituent groups has been synthesized to illustrate their conformational behavior. 4,22-dimethoxy-1,2-dimethyl[2.10]MCP-1-ene 3 was synthesized by a Grignard coupling reaction, Friedel-Crafts acylation reactions and McMurry coupling reaction from 1,10-dibromodecane. The formation of 4,22-dihydroxy-1,2-dimethyl[2.10]MCP-1-ene 4 was carried out by demethylation of compound 3 with boron tribromide at room temperature. The syn type conformation of 4 was characterized by X-ray diffraction and was found to form both intramolecular and intermolecular hydrogen bonds between the two hydroxyl groups. From this reaction an interesting compound [10]tetrahydrobenzofuranophane 5 was afforded on prolonging the reaction time. 5,21-diformyl-4,22-dihydroxy-1,2-dimethyl[2.10]MCP-1-ene 6 has been prepared from 4,22-dihydroxy-1,2-dimethyl[2.10]MCP-1-ene 4 by using the Duff method in the presence of hexamethylenetetramine. Structural analysis by 1H NMR spectroscopy and X-ray diffraction confirmed that both the solution and the crystalline state of compound 6 adopts an anti-conformation which forms an intramolecular hydrogen bond between the formyl group and the hydroxyl group, which is an interesting finding for long carbon chain MCP compounds

Demethylation of 5,n-di-tert-butyl-8,n-dimethoxy[2.n] metacyclophane-1-ynes with BBr3 to afford novel [n] benzofuranophanes

© 2016 Elsevier B.V. All rights reserved. Novel [n]benzofuranophanes (n = 8 & 10) 2a-b have been prepared by successive intramolecular cyclization from 5,19-di-tert-butyl-8,22-dimethoxy[n]metacyclophane-1-yne (syn-1a-b) by treatment with BBr 3 in CH 2 Cl 2 at room temperature for 8h. [2.n]Benzofuranophanes 2a-b were also obtained by treatment of 1,2-di-endo-bromo-5,19-di-tert-butyl-8,22-dimethoxy[n] metacyclophane (meso-3a-b) with BBr 3 in CH 2 Cl 2 by using the same reaction conditions. 1 H NMR spectra of 2a-b reveals the formation of intramolecular hydrogen bonding between hydroxyl proton with the oxygen of the furan moiety and X-ray analysis shows that the lengths between H (OH) and O (furan) are 1.981 and 1.823 Å, respectively. The conformation of [8]benzofuranophane 2a in solution is rigid with restricted rotation around the diaryl linkage rather than [10] benzofuranophane 2b because of weak intramolecular hydrogen bonding and the short length of the cross-linking chain

Synthesis, structures and Lewis‐Acid‐Induced isomerization of 8‐Methoxy[2.2]metaparacyclophanes and a DFT study

Methyl substituted 8‐methoxy[2.2]MPCPs 8 a–b were obtained via thiacyclophane and its oxidized products. Lewis acid‐catalyzed (AlCl3‐MeNO2) reactions of 5‐tert‐butyl‐8‐methoxy‐12,13,15,16‐tetramethyl[2.2]MPCP 8 b under various conditions led to transannular cyclization and isomerization reactions, affording the considerably less‐strained 5‐tert‐butyl‐8‐methoxy[2.2]MPCP 9, 5‐tert‐butyl‐8‐hydroxy‐14,16,17,18‐tetramethyl[2.2]metacyclophane 10 and pyrene derivatives 11 and 12. However,on prolonging the reaction time to 3 h for 8 b, the major product is 5‐tert‐butyl‐8‐hydroxy[2.2]MPCP 10. These reactions are strongly affected by the size and properties of the C‐8 substitutents as well as the methyl substitutents on the para‐linked benzene rings, which increase the strain in the molecules. The 1H NMR spectra and X‐ray crystallographic analysis of 8 b revealed that it adopts a syn‐conformation both in solution and in the solid state

Studies on Lewis-Acid Induced Reactions of 8-Methoxy[2.2]metacyclophanes: A New Synthetic Route to Alkylated Pyrenes

Anti-8-methoxy[2.2]metacyclophanes (MCPs) 5 a–b were obtained via pyrolysis of the corresponding syn-thiatetraoxide cyclophanes 4 a–b. Coupling reactions of 4-tert-butyl-1-methoxy-2,6-bis(mercaptomethyl)benzenes 1 a–b and 1,5-bis(chloro-methyl)-2,4-dimethylbenzene 2 under high dilution conditions afforded only the syn-conformers of 9-methoxy-2,11-dithia[3.3]metacyclophanes 3 a–b, which with m-CPBA formed the corresponding syn-tetraoxides 4 a–b. Lewis acid (TICl4/AlCl3-MeNO2) or iodine-catalyzed reactions of 5 b under various conditions led to transannular cyclization to afford tetrahydropyrene 6 b and pyrene derivative 7 b and/or de-tert-butylated 6 a. Iodine-catalyzed reaction of 5 a afforded tetrahydropyrene 6 a. These findings suggest the potential for a new route to alkylated pyrenes via strained and alkylated metacyclophanes. Density functional theory (DFT) studies were carried out to investigate the conformational characteristics of 3–5

Synthesis and conformational studies of calixarene analogue chiral [3.3.1]metacyclophanes

Trihydroxy[3.3.1]metacyclophane, which can be regarded as an unsymmetrical or incomplete “homocalix[3]arene”, has been prepared from trimethoxy[3.3.1]metacyclophane by demethylation with trimethylsilyl iodide in MeCN. Di-O-methylation at the lower rim of trihydroxy[3.3.1]metacyclophane in the presence of K₂CO₃ in acetone afforded a novel, inherently chiral calixarene–analogue, namely a macrocyclic [3.3.1]metacyclophane, possessing C₁ symmetry. The inherent chirality of the two conformers was characterized by ¹H NMR spectroscopy by addition of an excess of Pirkle's chiral shift reagent [(S)-(+)-1-(9-anthryl)-2,2,2-trifluoroethanol], which caused a splitting of the OMe group and AB patterns corresponding to the methylene protons

Aggregation‐induced emission luminogen: A new perspective in the photo‐degradation of organic pollutants

Both the variety and uniqueness of organic semiconductors has contributed to the rapid development of environmental engineering applications and renewable fuel production, typified by the photodegradation of organic pollutants or water splitting. This paper presents a rare example of an aggregation‐induced emission luminogen as a highly efficient photocatalyst for pollutant decomposition in an environmentally relevant application. Under irradiation, the tetraphenylethene‐based AIEgen (TPE‐Ca) exhibited high photo‐degradation efficiency of up to 98.7% of Rhodamine B (RhB) in aqueous solution. The possible photocatalytic mechanism was studied by electron paramagnetic resonance and X‐ray photoelectron spectroscopy spectra, electrochemistry, thermal imaging technology, ultra‐performance liquid chromatography and high‐definition mass spectrometry, as well as by density functional theory calculations. Among the many diverse AIEgens, this is the first AIEgen to be developed as a photocatalyst for the degradation of organic pollutants. This research will open up new avenues for AIEgens research, particularly for applications of environmental relevance