Selective synthesis of functionalized thia- and oxacalix[2]arene[2]pyrimidines

Functionalized oxacalix[m]arene[n]pyrimidines have been synthesized by S(N)Ar on 4,6-dihalopyrimidine building blocks. Depending on the S(N)Ar conditions, either a mixture of oxacalix[n]arenes, ranging from oxacalix[4]- up to oxacalix[12]arene, could be prepared or the oxacalix[4]arene could be synthesized selectively in a high yield. The electrophilic (pyrimidine) and the nucleophilic components could both be varied, allowing the preparation of functionalized oxacalix[4]arenes. Moreover, the procedure also gives access to the analogous thiacalix[4]arenes.     

Synthesis and structure characterization of unsymmetrical oxacalix[2]benzene[2]pyrazines

The synthesis of two unsymmetrically linked oxacalix[2]benzene[2]pyrazines (1 and 2) is described. X-ray single crystal structure analysis revealed a highly distorted 1,3-alternate conformation of compound 1 (containing ortho- and meta-diphenol components) and a distorted boat conformation of compound 2 (containing meta- and para-diphenol components). Oxacalix[2]benzene[2]pyrazine containing both ortho- and para-diphenol components was not obtained via similar synthetic strategy.     

Design,structure and anion recognition of larger-rim functionalized oxacalix[2]arene[2]triazine hosts

Larger-rim functionalized tetraoxacalix[2]arene[2]triazine host molecules were efficiently synthesized through a fragment coupling followed by AlCl₃-mediated deprotection/arylation protocol. Substituent effects, functions of counter cations on anion recognition in solution were systematically studied by means of fluorescence and NMR titrations.     

Synthesis and self-assembly of novel oxacalix[2]arene[2]triazine amphiphiles

Heteracalixaromatics are an emerging generation of macrocyclic host molecules in supramolecular chemistry. As a typical example of heteracalixaromatics, oxacalix[2]arene[2]triazine adopts a shape-persistent 1,3-alternate conformation and can be easily functionalized. Taking it as a platform, a series of oxacalix[2]arene[2]triazine-based amphiphiles bearing long alkyl chains were synthesized through post-macrocyclization functionalization or 3+1 fragment coupling protocols. The self-assembly behavior of these amphiphiles in a mixture of tetrahydrofuran (THF) and water was investigated. Dynamic light scattering (DLS) measurements revealed that the size of the self-assembled aggregates is dependent on the structure of the amphiphiles. The long alkyl chain substituents and/or intermolecular hydrogen bonds were found to promote the self-assembly.     

Quinoxaline-based U-shaped septuple-bridged [7,7]orthocyclophanes: synthesis, solid-state structure, and self-assembly

We report a three-step synthesis of 12 septuple-bridged [7,7]orthocyclophanes 11 comprising (i) two quinoxaline-based sidewalls and (ii) a linker built-in with a succinimide ring that carries phenyl, p-methoxyphenyl, p-hydroxyphenyl, or p-methoxybenzyl appendants. The synthesis began from the Diels-Alder adduct of 1,2,3,4-tetrachloro-5,5-dimethoxycyclopentadiene (1) and succinimide ring-fused dioxatetracyclodecadiene 9, followed by ruthenium-promoted oxidation of dichloroetheno-bridges in the adduct to generate a bis-α-diketone, which was then condensed with an arene-1,2-diamine to construct sidewalls (phane parts), furnishing U-shaped septuple-bridged [7,7]orthocyclophanes 11 embedding quinoxaline, dimethylquinoxaline, or benzoquinoxaline rings. Concentration-variant ¹H NMR spectra of N-p-methoxybenzyl substituted orthocyclophanes (11zd, 11xd, and 11yd) and single-crystal structures of four orthocyclophanes (11xa, 11yd, 11zb, and 11zd) revealed that the U-shaped septuple-bridged [7,7]orthocyclophanes 11 have a tendency of self-assembly, forming V-shaped dimeric entities driven chiefly by intermolecular π-π stacking interaction in both solid state and solution of high concentration.     

Synthesis and metal complexation studies of [2n]thiacalix[m]arene[m]pyrazine

Novel [2_n]thiacalixarenepyrazine and [2_n]thiacalixarenetriazine systems were synthesised by one-pot S_NAr reactions. A screening of the metal-complexing ability of [2₆]hexathiacalix[3]arene[3]pyrazine revealed its affinity for Cu^I, Cu^II and Ag^I metal salts.     

Odd-numbered oxacalix[n]arenes (n = 5, 7): synthesis and solid-state structures

The critical synthetic access to odd-numbered calix[n]arenes has evidently resulted in less attention for these macrocycles, although specific molecular recognition phenomena have been observed for some of them. A straightforward fragment coupling approach has been designed, applying kinetically controlled nucleophilic aromatic substitution reaction conditions, affording odd-numbered oxacalix[n]arenes (n = 5, 7) selectively in high yields. The solid-state conformational behavior and the oxacalix[n]arene cavity size were explored by single-crystal X-ray diffraction studies.     

Squaraine [2]catenanes: synthesis, structure and molecular dynamics

Three squaraine [2]catenanes are synthesized and found to have bright, deep-red fluorescence and high chemical stability. The interlocked molecules undergo two large-amplitude dynamic processes, twisting of the squaraine macrocycle and skipping over the partner tetralactam.     

o-Quinonoid heterocycles: synthesis and crystal structure of 2,3-dicyano-5,7-bismethylthieno[3,4-b]pyrazine

2,3-Dicyano-5,7-bismethylthieno[3,4-b]pyrazine (5), has been obtained as a minor product from reactions of S-nucleophiles with 5,6-di(1-bromoethyl)pyrazine-2,3-dicarbonitrile (3), or from a condensation of 4-hydroxy-2,5-dimethyl-2,3-dihydrothiophen-3-one (4) with diaminomaleonitrile. The molecular structure of compound 5 has been confirmed by X-ray diffraction. A partial separation of charge causes a donor-acceptor type arrangement of the planar molecules in uniform parallel stacks with an interplanar spacing of 3.334(2) A at 100 K.     

Diphenylmethylidenecyclobuta[a]cyclopropa[d]benzene: synthesis and spectral characterization

[reaction: see text] The first derivative of the novel and highly strained rocketene (cyclobuta[a]cyclopropa[d]benzene) 5, namely, the C4 diphenyl-substituted exocyclic alkene 8, has been prepared in 16% overall yield as a yellow oil with properties fully consistent with its highly strained nature.     

The clean and mild synthesis,crystal structure,and intra-molecular hydrogen bond study of substituted new 4,8-dihydropyrano[3,2-b]-pyrans containing chlorokojic acid moiety

Research on Chemical Intermediates - A safe, green and convenient process was developed for the synthesis of a novel group of 4,8-dihydropyrano[3,2-b]-pyrans by dialkyl acetylenedicarboxylates and...     

Catalytic synthesis of pyrazine, piperazine, and 1,4-diaza[2,2,2]-bicyclooctane

A study is made of the deamination of diethylenetriamine over acidalkali catalysts, i. e., kaolin and alumina with promoters. Promoters which raise the acidity of the catalyst, affect the formation of triethylene diamine favorably. Increasing the amount of additive increases the amount of triethylenediamine, and cuts the optimum temperature at which it is formed. On kaolin or Al₂O₃+15% B₂O₃, the yield of triethylenediamine amounts to 30% theory. Addition of MoO₃ facilitates dehydrodeamination and hydrogenolysis of the diethylenetriamine. The optimum promoter for preparing pyrazine is MoO₃ along with a small amount of acid oxides. On the Al₂O₃+5% MoO₃+1% P₂O₅, the pyrazine yield is 27.5% theory. Triethylenediamine can be separated from mixtures of it with piperazine by azeotropic distillation with mxylene or a mixture of mesitylene and -memylnaphthalene.     

Catalytic synthesis of pyrazine,piperazine, and 1,4-diaza[2,2,2]-bicyclooctane

A study is made of the deamination of diethylenetriamine over acidalkali catalysts, i. e., kaolin and alumina with promoters. Promoters which raise the acidity of the catalyst, affect the formation of triethylene diamine favorably. Increasing the amount of additive increases the amount of triethylenediamine, and cuts the optimum temperature at which it is formed. On kaolin or Al₂O₃+15% B₂O₃, the yield of triethylenediamine amounts to 30% theory. Addition of MoO₃ facilitates dehydrodeamination and hydrogenolysis of the diethylenetriamine. The optimum promoter for preparing pyrazine is MoO₃ along with a small amount of acid oxides. On the Al₂O₃+5% MoO₃+1% P₂O₅, the pyrazine yield is 27.5% theory. Triethylenediamine can be separated from mixtures of it with piperazine by azeotropic distillation with mxylene or a mixture of mesitylene and α-memylnaphthalene.     

Synthesis, structure, and conformation of ortho-linked oxacalix[n]arene[n]hetarenes

ortho-Linked oxacalix[n]arene[n]hetarenes (n=2, 3) were prepared by one-step cyclooligomerization of catechol and meta-dichlorinated nitrogen containing heterocycles or via a two-step reaction process. Solid state structure of the ortho-linked oxacalix[n]arene[n]hetarenes (n=2, 3) has been determined by X-ray crystallography. 1,3-Alternate and 1,3,5-alternate conformations were found for ortho-linked oxacalix[2]arene[2]pyrazine (1) and oxacalix[3]arene[3]pyrazine (2), respectively. However, a core conformation with C₃ symmetry was found for ortho-linked oxacalix[3]arene[3]pyrimidine (4), which is completely different from that of its isomer, compound 2.     

Oxamic acid derivaties in heterocyclic synthesis: Preparation of 1,2,4-triazolo[1,5-a]pyrazine derivatives

N-Aryl-N-(α-phenylphenacyl)oxamoyl chlorides react with N³-arylsubstituted amidrazones to give functionalized 1,2,4-triazoles which undergo ring-closure by the action of thionyl chloride to give 1,2,4-triazolo[1,5-a]-pyrazinium chlorides in excellent yields.     

Metal-metal bond formation between [n]metallocenophanes: synthesis and characterisation of a dicarba[2]ruthenocenophanium dimer

Feeling the strain: The first example of metal-metal bonding between strained [n]metallocenophanes is reported. A dicarba[2]ruthenocenophanium dimer has been synthesised through the oxidation of a dicarba[2]ruthenocenophane (see figure). The structural and electrochemical characterisation of the dimer is also discussed.     

2-(1H-pyrazol-3-yl)pyrazine: a polytopic N-donor ligand used to construct Cu-[2+2] molecular grid: synthesis,structure, and magnetic properties

Herein, we present a new polytopic N-donor, which is used to construct a metal–organic compound. The resulting metal–organic compound, Cu₄(L)₆(NO₃)₂ (HL=(1H-pyrazol-3-yl)pyrazine) (1), is synthesized by the hydrothermal reaction of Cu(NO₃)₂ and HL (ratio: 1?:?1). Single-crystal X-ray diffraction shows that 1 comprises a Cu-[2+2] molecular grid. Magnetic studies reveal antiferromagnetic interactions, interpreted by a simplified dinuclear mode.     

An expedient phosphine-catalyzed [4 + 2] annulation: synthesis of highly functionalized tetrahydropyridines

Ethyl 2-methyl-2,3-butadienoate acts as a 1,4-dipole synthon and undergoes [4 + 2] annulation with N-tosylimines in the presence of an organic phosphine catalyst. The resulting adducts, ethyl 6-substituted-1-(4-tosyl)-1,2,5,6-tetrahydro-pyridine-3-carboxylates, are formed in excellent yields with complete regioselectivity. Mechanistic reasoning for this new annulation has led to an expansion of the reaction scope by employing ethyl 2-(substituted-methyl)-2,3-butadienoates to give ethyl 2,6-cis-disubstituted-1-(4-tosyl)-1,2,5,6-tetrahydro-pyridine-3-carboxylates with high diastereoselectivities.     

Facial one-pot synthesis of D3h symmetric bicyclocalix[2]arene[2]triazines and their layered comb self-assembly

A number of D_3h symmetric bicyclocalix[2]arene[2]triazine core compounds were synthesized via a general and good-yielding (43–48% yield) facile protocol starting from cyanuric halides, phloroglucinol and K₂CO₃ under very mild reaction conditions. These cage-like compounds are tolerante with different reaction conditions and can be derived with other functional groups in high yields. The X-ray crystal structures show these compounds have slightly distorted D_3h symmetric structures. Due to the unique molecular topological structure, bicyclocalix[2]arene[2]triazine molecules form unique layered comb networks when hydrogen bond groups exist (such as CO₂H, B(OH)₂), which represent a new kind of building block unit for supramolecular architectures.     

Pyrazolino[60]fullerene-oligophenylenevinylene dumbbell-shaped arrays: synthesis, electrochemistry, photophysics, and self-assembly on surfaces

Symmetrically substituted oligophenylenevinylene (OPV) derivatives bearing terminal p-nitrophenylhydrazone groups have been prepared and used for the synthesis of dumbbell-shaped bis(pyrazolino[60]fullerene)-OPV systems. In these triad arrays, the OPV-type fluorescence is dramatically quenched as a consequence of ultrafast OPV-->C60 singlet energy transfer. In its turn the fullerene singlet state is quenched by pyrazoline-->C60 electron transfer, in line with the behavior of the corresponding reference fullerene molecule. The occurrence of electron transfer in the multicomponent arrays is evidenced by recovery of fullerene fluorescence at 77 K in CH2Cl2 and in toluene at 298 K. Under these conditions the OPV-->C60 energy transfer is unaffected. The rate of this process turns out to be higher for the OPV trimer than for the corresponding pentameric OPV arrays, in agreement with energy-transfer theory expectations. Scanning tunneling microscopy (STM) and scanning force microscopy (SFM) revealed that the bis(pyrazolino[60]fullerene)-OPV can self-assemble into ordered layered crystalline architectures on the basal plane of highly oriented pyrolitic graphite.