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Synthetic routes were developed to attach three redox-active metal fragments to cross-conjugated 3-methylidenepentadiyne covalently expanded by diazafluorenylidene: The two alkyne termini of this n...

The synthesis of an enediyne molecule functionlized with different metal coordination sites in a cross-π-conjugated fashion is reported. Using Pd-mediated cross-coupling reactions, 2,2'-bipyridine units were attached at the periphery of diazafluorenemethylidene to obtain a multitopic ligand. UV-vis spectrosopic investigations along with electrochemical analyses reveal electronic communication along the conjugated path reflected in red-shifted absorption spectra and shifts of reduction potentials. The properties of the ligand could be manipulated by coordinating [Ru(bpy)

We have performed the syntheses of a novel pyrene-porphyrazine conjugate (ZnPzPy) and a reference porphyrazine (ZnPz) to promote the wet-chemical exfoliation of graphite based on the synergetic use of ultrasonication, centrifugation, and doping. ZnPzPy features, on one hand, a hydrophobic pyrene to anchor onto the basal plane of graphene, and, on the other hand, an amphoteric porphyrazine to either p- or n-dope graphene. To this end, we have characterized individual building blocks, that is, ZnPzPy and exfoliated graphite, and the resulting electron donor-acceptor nanohybrid, that is, ZnPzPy/graphene (ZnPzPy-G), by means of an arsenal of microscopic and spectroscopic techniques. From a full-fledged characterization we conclude that ZnPzPy facilitates the exfoliation of graphite affording suspensions featuring 9.5% of single- or few-layered ZnPzPy-G with a mean average size of 200 ± 140 nm. Importantly, a notable shift of charge density from graphene to ZnPzPy in the ground state of ZnPzPy-G corroborates the preference of exfoliated graphite to undergo p-doping rather than n-doping. As an immediate consequence, a full charge separation leads in the excited state to a 750 ± 150 ps lived charge separated state.

Unprecedentedly large subporphyrazines (SubPz) with dibenzoquinoxalino-fusion and peripheral phenyl substitution were prepared by the cyclization of perfluorated or non-fluorous polyphenyl-substituted quinoxaline dinitriles and characterized by spectroscopic techniques. The compounds suitability to act as photosensitizers was explored by wavelength-specific induction of singlet oxygen luminescence and was shown to be excellent. Determination of 1O2-quantum yields suggests that fluorine substitution enhances the photosensitization efficiencies of the SubPz. On the other hand, cyclic voltammetry reveals an increase of irreversible reductive processes in case of the fluorinated SubPz.

Four benzodehydroannulene subunits were implemented on a dibenzoquinoxalinopoprhyrazine core using efficient palladium-mediated alkyne coupling and oxidative acetylene coupling on phenanthrene dione precursors. Despite the significant amount of strain in system, as evidenced by X-ray analysis of an immediate precursor, porphyrazine assembly leads to an extended model for N-doped graphyne with photosensitizing properties.

The quality and durability of adhesive bonds are affected by aging processes. Therefore, appropriate monitoring for early damage detection is essential for such bonds. For these reasons, we set out to develop an adhesive-based joining technology that makes early detection of potential defects in adhesive bonds possible. In this method, various dyes are added to the adhesive used, which indicate, if the specific load is exceeded. These dyes are micro-encapsulated through different methods, producing capsules of different sizes and wall thicknesses. When an adhesive bond is damaged or overloaded, the capsule would break and the dye would be released. The released colors can be detected optically or with suitable measurement systems. To demonstrate this technology, various experiments were carried out. Firstly, changes in adhesive properties were checked through thermal analysis and then pure substance specimens were produced and tested as means of comparison. Finally, the formulated adhesives were used to produce specimens for compressive shear tests, using glass and aluminium. The advantage of this technology by comparison to conventional nondestructive testing methods is the possibility to detect defects in adhesive bonds before the durability of the adhesive bond itself is affected.

Reaction of lithiated 1-(1-ethoxy-3-phenyl-prop-2-ynyl)-1H-benzotriazole (3) with various acetylenic aldehydes followed by periodinane oxidation and hydrolysis yields terminally protected 1-phenyl-1,5-hexadiyne-3,4-diones 7a–d as the first examples of dialkynyl-1,2-diones.

2,9-Disubstituted and 3,8-disubstituted 1,10-phenanthrolines have been converted to the respective 5,6-diamines in three steps. The new heterocycles have been employed in condensation reactions with a protected 1,2-dialkynyl-1,2-dione to afford solubility-improved, acetylenic pyrazinophenanthrolines (pyzphen). In an initial study, the synthetic scope of these novel acetylenic ligands is evaluated.

New aryl-terminated octaalkynyl tetrapyrazinoporphyrazines were prepared in three steps starting from functionalised bisarylalkynyl 1,2-diones. While the tert-butylphenyl substituents were shown to aid solubility in organic solvents and to reduce chromophore aggregation efficiently, more hydrophilic tetrapyrazinoporphyrazines were obtained through the use of polyethylene glycol-substituted (PEG-substituted) phenyl groups. The absorption profiles and the singlet oxygen quantum yields of the acetylenic tetrapyrazinoporphyrazines were determined with a view to assess their suitability for PDT applications. In all cases the presence of the terminal aryl moieties resulted in noticeable bathochromic and hyperchromic shifts of the lowest-energy absorption maxima to 680 nm and of the extinction coefficients to beyond 320000. If magnesium is coordinated in the centre of the acetylenic tetrapyrazinoporphyrazines the compounds have singlet oxygen quantum yields of 0.40 in THF. With zinc as the central metal ion, the singlet oxygen quantum yields in the same solvent increase to 0.70. The absorption characteristics of the newly prepared chromophores, as well as their ability to generate singlet oxygen, suggest that these phthalocyanine analogues are interesting candidates as PDT-sensitisers. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Acetylenic quinoxalinodehydro[12]- and -[24]annulenes have been prepared from Boc-protected aminobenzodehydroannulenes and diethynyl-1,2-diones. For the smaller annulene, theoretical and spectroscopic studies reveal π-delocalisation over the entire aromatic system, including the external acetylenes. In contrast, the larger annulene prevails in a tub-like conformation, which limits π-orbital overlap and gives rise to higher-energy absorption and emission maxima.

A range of lipo- and hydro- philic derivatives of the new class of octaalkynyl tetra-(6,7)-quinoxalinopor- phyrazines (TQuiPors), analogues of the naphthalocyanines, were prepared in two steps starting from functionalised hexa-1,5-diyne-3,4-diones. Divalent zinc and magnesium ions were introduced into the macrocyclic core. Whereas the triisopropylsilyl-, 3,5-di-tert-butylphen- yl- and 4-triisopropylsilyloxyphenyl-ter- minated acetylenic TQuiPors are lip- ophilic and hence soluble in standard organic solvents, a polyethylene glycol- substituted derivative was found to dis- solve in DMSO as well as in ethanol/ water mixtures. The new chromophores are characterised by intense UV/Vis/ NIR absorptions, most notably by bands at 770 nm with extinction coefficients exceeding 500 000 1 cm 1 . With a view to possible photodynamic therapy appli- cations, the potency of the chromo- phores to sensitise the formation of singlet oxygen was examined, both qual- itatively using a 1,3-diphenylisobenzo- furan assay, and quantitatively by the determination of the singlet oxygen quantum yields. It was found that all TQuiPors produce singlet oxygen when irradiated in the presence of air. In particular, the octaalkynyl Zn-TQuiPor generates singlet oxygen with a quantum yield of 56 %, thereby rivalling, and, in conjunction with its absorption profile, even exceeding the standards set by established PDTagents. T he photosta- bilities of the TQuiPors were assessed and generally found to be satisfactory, but dependent on the solvent and the wavelength of the incident light.

Aryl- and silyl-terminated 6,7-dialkynylpyrazino[2,3-f][1,10]phenanthrolines (pyzphen) have been prepared by the condensation of [1,10]phenanthroline-5,6-diamine with appropriately functionalised dialkynyl-1,2-diones. These new ligands were used as chelators in the formation of the corresponding [Ru(bpy)2(pyzphen)]·2PF6 and [Ru(phen)2(pyzphen)]·2PF6 complexes. The terminally free diethynyl [Ru(bpy)2(pyzphen)] complex, obtained by protodesilylation of a silyl-protected precursor, was shown to be amenable to oxidative acetylene hetero-coupling reactions with arylacetylenes and allowed the preparation of the corresponding butadiynyl-substituted derivatives. Homo-coupling reactions of the terminally free diethynyl [Ru(bpy)2(pyzphen)] complex to produce cyclic dehydroannulene-arrays were successful, but furnished an inseparable mixture of compounds of at least two different ring sizes. The photophysical and electrochemical properties of both the free ligands and their Ru(II)-complexes are clearly modified by the presence of the alkynyl substituents. In comparison with non-acetylenic model compounds it was established that acetylene substitution induces bathochromically shifted electronic absorptions and emissions to various degrees in ligands and complexes, leads to increased luminescence lifetimes and quantum yields of the ruthenium pyzphen complexes, and renders the acetylenic ligands and their complexes more susceptible to electrochemical reduction.

The electronic structures and transition energies of the title compounds are studied computationally using time-dependent density functional theory. A computationally tractable model chemistry is established, involving the local density approximation in conjunction with double-zeta plus polarisation basis sets. Solvent effects are included via the conductor-like screening model. Good agreement is found between the computationally determined geometric structures of several of the title systems and those found experimentally for related molecules. The electronic transition energies of all of the systems studied are found to be strongly influenced by the dihedral angle between the aryl rings and the backbone of the diazabutadiene unit. Satisfactory interpretation (at the molecular orbital level) of experimentally determined electronic absorption spectra is obtained using computational model compounds in which the acetylenic iPr3Si substituents are replaced by hydrogen atoms. Inclusion of the iPr3Si units in the calculations leads to a simulated spectrum which is more complicated than that of the H-substituted system. Comparison with experiment does not conclusively establish if the iPr3Si units are required in the computational model. The implications for future simulations of the electronic absorption spectra of diazabutadiene complexes of transition metals are discussed.

6H-Isoindolo[2,1-a]indoles (5, 7, 10, 13), 5,6-dihydroindolo[2,1-a]isoquinolines (20, 21), and 6,7-dihydro-5H-benzo[c]azepino[2,1-a]indoles (23, 25, 27, 30) have been prepared as melatonin analogues to investigate the nature of the binding site of the melatonin receptor. The affinity of analogues was determined in a radioligand binding assay using cloned human mt1 and MT2 receptor subtypes expressed in NIH 3T3 cells. Agonist and antagonist potency was measured using the pigment aggregation response of a clonal line of Xenopus laevis melanophores. The 2-methoxyisoindolo[2,1-a]indoles (7a−d) showed much higher binding affinities than the parent isoindoles (5a−e), and whereas 7a−c were agonists in the functional assay, 7d and 5a−e were antagonists. The 2-ethoxyisoindolo[2,1-a]indoles (10a−d) showed reduced binding affinities compared to their methoxy analogues, while the 5-chloro derivative 13 showed a considerable reduction in binding affinity and potency compared to 7a. The 10-methoxy-5,6-dihydroindolo[2,1...

Two new routes to cross-conjugated 3,4-dimethylenehexa-1,5-diynes, both starting from dialkynyl 1,2-diones, have been devised. Whereas triisopropylsilyl-protected diketones could be diolefinated in a bis-Wittig reaction with methylenetriphenylphosphorane, their aryl-terminated congeners had to be subjected to the conditions of the Peterson olefination (trimethylsilylmethylmagnesium chloride and subsequent dehydration of the resulting diol with thionyl chloride). The reactivity of the diethynylbutadienes towards standard dienophiles was found to be low and alternative thermal reactions compete with [4 + 2] cycloadditions. However, dicyanoacetylene was shown to be an effective cycloaddition partner leading, after aromatisation, to the corresponding dicyanodiethynylbenzenes. These were cyclotetramerised with magnesium butanolate in butanol to furnish octaalkynylphthalocyanines, thereby completing a concise, three-step synthesis of these NIR chromophores of relevance to photodynamic forms of therapy.

Acetylenic diazabutadienes (DADs) were used to modulate the electron absorption properties of Ni(0) and Ni(II) chelate complexes with respect to those of non-acetylenic DAD metal coordination compounds. Alkynylated bis( N -aryl) DAD ligands are shown to induce efficient metal-to-ligand charge-transfer in coordination compounds of the type (DAD) 2 Ni(0). These metal–ligand interactions manifest themselves as intense absorptions in the near infrared (NIR) around 800 nm and are significantly shifted batho- and hyperchromic compared to charge-transfer bands of non-acetylenic DAD metal complexes. Likewise, alkynyl substitution of bis(glyoximato)nickel(II) complexes results in a sizeable absorption band in the visible region of the electromagnetic spectrum.

The introduction of alkynyl groups into the 2,3-positions of the 1,4-diazabuta-1,3-diene (DAD) backbone succeeds along two complementary synthetic routes either by condensing triisopropylsilyl-terminated dialkynyl-1,2-diones with primary aromatic amines or by a palladium-mediated alkynylation of bis(imidoyl chlorides). X-ray crystallographic analyses of two dialkynyl DAD derivatives reveals their planar (E-s-trans-E) conformations in the solid state. However, the central CC bond of both DAD backbones investigated has a length of 1.491(2) A, and is therefore too long to indicate efficient delocalization across the DAD core. The UV/Vis spectra of dialkynyl DADs demonstrate that their absorptions in comparison to those of non-alkynyl DADs are bathochromically shifted by more than 40 nm, thereby demonstrating the suitability of the title compounds for developing NIR chromophores. The electron absorption properties of differentially N,N′-disubstituted dialkynyl DADs gave no indication for a push-pull effect across the DAD skeleton and suggest the ynimine moiety as the active chromophore of dialkynyl DADs. The electrochemical properties of the title compounds were determined by cyclo- and steady state voltammetry and show that introducing alkynyl groups leads to more easily reducible DAD systems. Again, the perception of dialkynyl DADs as covalently linked, but electronically decoupled ynimine units is corroborated by the redox potential of a differentially N,N′-disubstituted dialkynyl DAD. Similar conclusions were drawn from semiempirical MO (PM3) calculations of dialkynyl DADs.

Starting from o-phenylenediamine, we have developed a new and reliable route to 1,2-diamino-4,5-phthalodinitrile that is based on the reductive desulfurisation of 5,6-dicyano-2,1,3-benzothiadiazole with sodium borohydride. The reaction sequence uses only cheap reagents and relies on simple recrystallisations for the purification of all intermediates.

A general procedure for a palladium-mediated organyl group transfer from organostannanes to bis(imidoyl chlorides) has been developed on the basis of the Pd 2 (dba) 3 ·CHCl 3 /AsPh 3 catalyst system. This protocol allows the synthesis of 2,3-dialkynyl-1,4-diazabutadienes and of trialkynyl-1,3,5-triazines from cyanuric chloride. © 1997 Elsevier Science Ltd.

A convenient procedure for the preparation of symmetrically end-protected dialkynyl-1,2-diones 3 from lithium acetylides and oxalyl chloride in the presence of CuBr and LiBr is described. The condensation of 3 with various aromatic and heteroaromatic 1,2-diamines leads to pyrazine-based α-dialkynylated heterocycles. The enediyne substructure of diethynylquinoxaline can be thermally rearranged in a Bergman cyclization reaction.

The structure of bis(4-tert-butyl-2,6-dimethylphenyl)hexa-1,5-diyne-3,4-dione, C 30 H 34 O 2 , has been determined, revealing an extended s-trans conformation of the dione and the two ynone moieties, which are shielded by the flanking methyl substituents. The structural parameters and the packing arrangement suggest little electronic delocalization between the two ynone moieties.

Wie optimiert man die Oberflache von Keramikkacheln, damit Raumfahrzeuge beim Eintauchen in die Erdatmosphare effektiv vor Hitze geschutzt werden? Welchen Einfluss hat die Teilchengrose der Zusatze einer Gummimischung auf den Grip eines Autoreifens? Wie formt man Farbpigmente, damit ein schimmernder Perglanzeffekt entsteht? Wie bringt man einen pharmazeutischen Wirkstoff unverandert und funktionsbereit an seinen zellularen Wirkort? Welche Komponenten benotigt ein optischer Computer?

The redox properties of tetraethynylethenes and carbon-rich molecular rods and dehydroannulenes built from these fully cross-conjugated molecular construction units are reported here for the first time. All monomeric and oligomeric cyclic and acyclic tetraethynylethenes are difficult to oxidize but undergo stepwise reductions, with the number of distinct steps increasing with the length of the linearly conjugated all-carbon backbone and the size of the Π system. The reductions are also facilitated when the length of the carbon backbone and the number of Π electrons in the molecules increase.

The first systematic electrochemical study by cyclic voltammetry (CV) and rotating-disk electrode (RDE) of the changes in redox properties of covalent fullerene derivatives (2–11) as a function of increasing number of addends is reported. Dialkynylmethanofullerenes 2–4 undergo multiple, fullerene-centered reduction steps at slightly more negative potentials than C60 (1; see Table and Fig. 1). The two C-spheres in the dumbbell-shaped dimeric fullerene derivative 4 show independent, identical redox characteristics. This highlights the insulating character of the sp3-C-atoms in methanofullerenes which prevent through-bond communication of substituent effects from the methano bridge to the fullerene sphere. In the series of mono- through hexakis-adducts 5–11, formed by tether-directed remote functionalization, reductions become increasingly difficult and more irreversible with increasing number of addends (see Table and Fig. 2). Whereas, in 0.1M Bu4NPF6/CH2Cl2, the first reduction of mono-adduct 5 occurs reversibly at −1.06 V vs. the ferrocene/ferricinium couple (Fc/Fc+), hexakis-adduct 11 is reduced irreversibly only at − 1.87 V. Hence, with incremental functionalization of the fullerene, the LUMO of the remaining conjugated framework is raised in energy. Reduction potentials are also dependent on the relative spatial disposition of the addends on the surface of the fullerene sphere. Observed UV/VIS spectral changes and changes in the chemical reactivity along the series 5–11 are in accord with the results of electrochemical measurements. Further, with increasing number of addends, the oxidation of derivatives 5–11 becomes more reversible. Whereas oxidations are increasingly facilitated upon going from mono-adduct 5 (+1.22 V) to tris-adduct 7 (+0.90 V), they occur at nearly the same potential (+0.95 to +0.99 V) in the higher adducts 8–11. This indicates that the oxidations occur in these compounds at a common sub-structural element, for which a ‘cubic’ cyclophane is proposed (see Fig. 3). This sub-structure is fully developed in hexakis-adduct 11.

The title compound (AHTN-OH), C17H26O, was prepared in order to provide standard materials for the qualitative and quantitative analysis of environmental pollutants. The molecule possesses a chiral C atom, although the structure determination was performed on racemic material, expressed in the structure as disordered chiral sites. The asymmetric unit consists of four AHTN-OH molecules containing an hydroxy group and forming a tetrameric cyclic motif built up by four strong hydrogen bonds between these hydroxy groups and additionally by two weak C—H...π interactions. Furthermore, these tetramers are linked via very weak C—H...π interactions, forming chains along the c axis.

The influence of [pi] delocalization on the geometry of benzene is examined at the ab initio SCF level of theory. We find that benzene favors a bond alternating geometry when its canonical [pi] MOs are replaced by three localized ethylenic orbitals, revealing that delocalization is in part responsible for the equilibrium symmetric structure. In apparent contrast, a [sigma]-[pi] energy partitioning analysis suggests that the benzene [sigma] framework is responsible for the symmetric structure, the [pi] system preferring a distorted geometry. Shaik et al. have therefore concluded that delocalization in not an important symmetrizing force in this molecule. We show, however, that the [pi] energy component contains a sizable and strongly geometry dependent contribution from the localized (Kekule) wave function. Thus, it appears to be misleading to judge the nature of delocalization based on a [sigma]-[pi] partition. We conclude that delocalization effects act to strongly stabilize symmetric benzene in essential accord with the concepts of classical resonance theory. 27 refs., 6 figs., 2 tabs.

The synthesis and complete characterization of 17 new fullerene-acetylene covalent derivatives is described. Reaction of 3-bromo-1,5-bis(trimethylsilyl)penta-1,4-diyne (5) with C60 gave bis-protected diethynylmethanofullerene 4 in 56% yield. Unsymmetrically bis-protected diethynylmethanofullerene 6 was synthesized in 53% yield from tosylhydrazone 7 and C60. Proto-desilylation of 4 and 6 gave the corresponding free alkynes 3 and 8 in 83% and 69% yield, respectively. Partial deprotection of 4 afforded mono-protected fullerene 9 in 35% yield. Oxidative hetero-coupling reactions of 3 and 8 under Hay conditions with various monosubstituted acetylenes gave the butadiynylmethanofullerenes 10–13 in yields varying from 25–49%. Homo-coupling of 8 produced dumbbell-shaped fullerene 14, the first dimeric fullerene that could be fully characterized. The X-ray crystal structure analysis of 14 revealed little or no electronic interaction between the two fullerene spheres. Addition of lithium trimethylsilylacetylide to C60 gave access to 1-substituted-2-(trimethylsilylethynyl)fullerenes. The acidity of hydrofullerene 16, synthesized in 58% yield, was studied as a function of base and solvent. Reaction of lithiated fullerene 17 with various electrophiles is discussed. Alcohol 25 was prepared in 57%yield by reaction of 17 with formaldehyde. Under strongly basic conditions, 25 eliminates formaldehyde to give 16 in quantitative yield. Oxidation of 25 afforded aldehyde 27 in 53% yield, a rather unstable compound that is easily converted to hydrofullerene 16. Conversion of 25 to the corresponding tosylate could be performed in 40% yield.

Reaction of lithiated 1-(1-ethoxy-3-phenyl-prop-2-ynyl)-1H-benzotriazole (3) with various acetylenic aldehydes followed by periodinane oxidation and hydrolysis yields terminally protected 1-phenyl-1,5-hexadiyne-3,4-diones 7a–d as the first examples of dialkynyl-1,2-diones.

A convenient procedure for the preparation of symmetrically end-protected dialkynyl-1,2-diones 3 from lithium acetylides and oxalyl chloride in the presence of CuBr and LiBr is described. The condensation of 3 with various aromatic and heteroaromatic 1,2-diamines leads to pyrazine-based α-dialkynylated heterocycles. The enediyne substructure of diethynylquinoxaline can be thermally rearranged in a Bergman cyclization reaction.

The need for new chromophores with intense absorptions at the far red end or the near infrared region of the electromagnetic spectrum is evident from recent developments in materials science and medicinal chemistry. This has prompted us to explore the potential of octaalkynyl-substituted phthalocyanines, tetrapyrazinoporphyrazines, and tetra-6,7-quinoxalinoporphyrazines. In order to assemble these chromophores efficiently and in a modular fashion, we have prepared two types of acetylenic building blocks − namely 3,4-dimethylenehexa-1,5-diynes and hexa-1,5-diyne-3,4-diones − and have successfully converted them into alkynyl-substituted benzenoid phthalonitriles, the former by means of cycloadditions with dicyanoacetylene, the latter through condensation reactions with vicinal diamines such as diaminomaleodinitrile and 4,5-diaminophthalonitrile. The dinitriles were cyclotetramerised to the corresponding octaalkynyl phthalocyanines and phthalocyanine analogues using magnesium butoxide in butanol. Core physical properties of the new chromophores, most notably their solubilities and absorptivities, are markedly influenced by the presence of the eight alkynyl substituents. Further fine-tuning of these characteristics by appropriate choice of terminal acetylene substituents is possible.

The geometries of benzene incrementally fused to cyclobutenes, 3,4-dimethylenecyclobutenw, and cyclobutadienes are investigated with ab initio SCF-MO methods and by natural bond orbital (NBO)/natural resonance theory (NRT) analysis, These systems show various degrees of bond alternation in the six-membered ring with fused bonds elongated and bonds adjacent to the site of annelation contracted compared to those of benzene. NBO analysis reveals significant strain in the σ-frame as evidenced by strong rehybridization at the annelated carbon centers

Peripheral alkynyl substitution of strongly absorbent chromophores, among them porphyrins1 and the phthalocyanines,2 is becoming an increasingly popular strategy for the design of functional dyes and molecular devices. The interest in structural modifications of this kind arises mainly from two factors. First, the acetylenic units enlarge the π-systems of the chromophores and induce bathochromic shifts in the electron absorption and emission spectra. Second, terminal alkynyl groups can be invoked to serve as covalent linkers for the assembly of delocalized multichromophor chains or two-dimensional polymer networks. Although peralkynylation of a given chromophor is often hampered by the tedious preparation of suitable precursors,2a a lower degree of alkynyl substitution frequently results in the formation of a mixture of regioisomers. We have therefore explored the possibility of employing small acetylenic building blocks for the rapid assembly of alkynylated chromophores. We report herein a short synthesis of 2,3,9,10,16,17,23,24-octalkynyl tetrapyrazinoporphyrazines3 (TPyPors) 1 from oxalyl chloride, along with some of the optical properties associated with the 72 π-electrons of 1.

Starting from o-phenylenediamine, we have developed a new and reliable route to 1,2-diamino-4,5-phthalodinitrile that is based on the reductive desulfurisation of 5,6-dicyano-2,1,3-benzothiadiazole with sodium borohydride. The reaction sequence uses only cheap reagents and relies on simple recrystallisations for the purification of all intermediates.

A provacative question is asked by the title. Explosions will probably not become a general synthetic method, but strained dehydrobenzoannulenes decompose explosively upon heating to give, inter alia, structured, fullerenoid carbon particles. The spectacular thermochemical behavior of these cycloalkynes has fueled hopes that acetylenic cyclophanes such as 1 can be prepared and brought to coalesce to spherical forms of carbon like the fullerenes. Promising progress in this area has recently been made and is highlighted in this contribution.

A series of 7-substituted melatonin and 1-methylmelatonin analogues were prepared and tested against human and amphibian melatonin receptors. 7-Substituents reduced the agonist potency of all the analogues in the Xenopus laevis melanophore assay, 7-bromomelatonin (5d) and N-butanoyl 7-bromo-5-methoxytryptamine (5f) being the most active compounds, but both were 42-fold less potent than melatonin (1). Whereas all the analogues bind with lower affinity at the human MT(1) receptor than melatonin, 5d, 5f and N-propanoyl 7-bromo-5-methoxytryptamine (5e) show a similar binding affinity to melatonin at the MT(2) receptor and consequently show some MT(2) selectivity. These results suggest that the receptor pocket around C-7 favours binding by an electronegative group, suggesting an electropositive region in this area of the receptor.