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

A hexahomotrioxacalix[3]arene-based ditopic receptor for alkylammonium ions controlled by Ag + ions 4

A receptor cone-1 based on a hexahomotrioxacalix[3]arene bearing three pyridyl groups 21 was successfully synthesized, which has a C3-symmetric conformation and is capable of binding 22 alkylammonium and metal ions simultaneously in a cooperative fashion. It can bind 23 alkylammonium ions through the -cavity formed by three aryl rings. This behaviour is consistent 24 with the cone-in/cone-out conformational rearrangement needed to reorganize the cavity for 25 endo-complexation. As a C3-symmetrical pyridyl-substituted calixarene, receptor cone-1 can also 26 bind a Ag + ion and the nitrogen atoms are turned towards the inside of the cavity and interact with 27 Ag +. After complexation of tris(2-pyridylamide) derivative receptor cone-1 with Ag + , the original 28 C3-symmetry was retained and higher complexation selectivity for n-BuNH3 + versus t-BuNH3 + was 29 observed. Thus, it is believed that this receptor will have a role to play in the sensing, detection, and 30 recognition of Ag + and n-BuNH3 + ions. 3

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

Проблема достоверности научного знания

Знание в самом общем виде можно определить как верное отражение в сознании человека явлений материального и духовного мира и, в частности, многообразных явлений общественной жизни

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

Fluorescent turn-on sensors based on pyrene-containing Schiff base derivatives for Cu2+ recognition: spectroscopic and DFT computational studies

A new fluorescent chemosensor L1, pyrene containing long chain Schiff base derivative in 1-position has been synthesized. Similarly, the receptors L2 and L3 are also designed in order to compare the binding ability for detection of Cu2+. The receptors exhibit very weak fluorescence (Φ = 0.01) due to the photoinduced electron transfer (PET). Upon addition of 10 equiv. of Cu2+, the emission intensity of ligands L1 and L2 are increased 65-fold (Φ = 0.31) and 25-fold (Φ = 0.08) in CH3CN/CH2Cl2 solvents system respectively. NMR titration experiments, spectroscopic and DFT computational studies confirmed the binding phenomena and sensitivity of Cu2+

Synthesis and evaluation of a novel ionophore based on a thiacalix[4]arene derivative bearing imidazole units

O-Alkylation of the flexible thiacalix[4]arene 1 with 2-chloromethyl-1-methyl-1H-imidazole 2 in the presence of Na₂CO₃ or K₂CO₃ afforded mono-O-alkylation product 3 in 29–51% yield, along with recovery of the starting compound. In contrast, the same reaction in the presence of Cs₂CO₃ gave only one pure stereoisomer, namely 1,3-alternate-4; other possible isomers were not observed. Alkali metal salts such as Na₂CO₃ and Cs₂CO₃ can play an important role in the conformer distribution via a template effect. The conformations of the receptors, mono-O-alkylation product 3 and that of 1,3-alternate-4, have been confirmed by X-ray crystallography. Furthermore, the complexation properties of the receptor 1,3-alternate-4 toward selected alkali/transition metal cations are reported. The two-phase solvent extraction data indicated that 1,3-alternate-4 exhibited a stronger extraction efficiency for transition metals over alkali metals. The dichromate anion extraction ability of 1,3-alternate-4 showed that it could serve as an efficient extractor of HCr₂O₇⁻/Cr₂O₇²⁻ anions at low pH

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

[2,2′-Imino­diethano­lato(2−)-κ3 O,N,O′][4-(meth­oxy­carbonyl­meth­yl)phen­yl]boron

The title compound, C13H18BNO4, was readily obtained from the reaction of methyl 4-boronobenzene acetate with ethano­lamine. A combination of inter­molecular N—H⋯O hydrogen bonds and C—H⋯π inter­actions leads to the pairwise association of mol­ecules

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