Thermochemistry and photochemistry of spiroketals derived from indan-2-one: stepwise processes versus coarctate fragmentations

Coarctate reactions are defined as reactions that include atoms at which two bonds are made and two bonds are broken simultaneously. In the pursuit of the discovery of new coarctate reactions we investigate the fragmentation reactions of cyclic ketals. Three ketals with different ring sizes derived from indan-2-one were decomposed by photolysis and pyrolysis. Particularly clean is the photolysis of the indan-2-one ketal 1, which gives o-quinodimethane, carbon dioxide and ethylene. The mechanism formally corresponds to a photochemically allowed coarctate fragmentation. Pyrolysis of the five-ring ketal yields a number of products. This is in agreement with the fact that coarctate fragmentation observed upon irradiation would be thermochemically forbidden, although this exclusion principle does not hold for chelotropic reactions. In contrast, fragmentation of the seven-ring ketal 3 is thermochemically allowed and photochemically forbidden. Upon pyrolysis of 3 several products were isolated that could be explained by a coarctate fragmentation. However, the reaction is less clean and stepwise mechanisms may compete

Coordination-Induced Spin-State-Switch (CISSS) in water

We present a non-ionic water-soluble porphyrin that does not exhibit measurable aggregation even at high concentrations in water. The spin state of the corresponding nickel(II) complex changes from completely diamagnetic (low- spin) to paramagnetic (high-spin) upon addition of a strong axial ligand. This leads to a strongly reduced NMR relaxation time of the water protons even at low concentrations of the complex

5-Chloro-2-(phenyl­diazen­yl)pyridine

In the title compound, C11H8ClN3, the azo group adopts a trans conformation and the dihedral angle between the six-membered rings is 15.47 (8)°

Straightforward syntheses of biradical-producing bicyclic dienediynes—dienediyne ketones cycloaromatize ia the Saito–Myers and not ia the neocarzinostatin pathway

The dienediyne models 23 and 28 of the pharmacophore of the antitumor natural product neocarzinostatin were prepared. Each synthesis requires only six steps from a-formylcyclohexanone. Our approach uses two key steps. The Ðrst consists of one-pot biscoupling reactions between propargyl alcohol, 2,2-dimethyl-3-butyn-1-ol and the bis(enoltriÑuoromethanesulfonate) 17. The second key step corresponds to ring-closing pinacol coupling reactions of the dialdehydes 20 and 25. The dienediyne models 23 and 28 cycloaromatized efficiently when treated with methyl thioglycolate and 1,4-cyclohexadiene at 25 ¡C via a SaitoÈMyers cyclization4 (to give the octahydroanthracenones 29, iso-29 and octahydrophenanthrenones 34, 35, respectively); in addition, we isolated compounds tentatively assigned as the octahydrobenzazulenones 30 and iso-30, which would stem from a competing Schmittel cyclization. According to density functional theory (B3LYP/6-31G*) and ab initio calculations [CASMP2(2.2)/6-31G//CAS(2.2)/6-31G], the core structures of the octahydroanthracenones and octahydrophenanthrenones obtained here and elsewhere form via the SaitoÈMyers cyclization of enyneallenyl ketones 53 to toluene-a,meta biradicals 55 and not via neocarzinostatin-like cycloaromatizations of the tautomeric enyne[3]cumulenols 54 to styrene a,meta-biradicals 56. This is so because, on the one hand, the two cyclization modes are predicted to have similar activation barriers (SaitoÈMyers: 16.0 kcal mol~1; neocarzinostatin type: 18.3 kcal mol~1) but, on the other hand, the enyneallenyl ketone 53 is a much more stable (21.1 kcal mol~1) cycloaromatization substrate than the enynecumulenol 54. In addition, the SaitoÈMyers cyclization product 55 is calculated to be considerably more stable (35.3 kcal mol~1) than the neocarzinostatin-type cycloaromatization product 56

Проектна діяльність бібліотек та інформаційних установ

Робоча навчальна програма «Проектна діяльність бібліотек та інформаційних установ» за напрямом підготовки 6.020102 «Книгознавство, бібліотекознавство і бібліографія», галузі знань 0201 «Культура», освітній рівень: перший (бакалаврський). - 2017 р

Lichtgesteuerte Konstruktion und Zerstörung: Schaltung zwischen zwei unterschiedlich zusammengesetzten käfigartigen Komplexen

Wir berichten über zwei regioisomere Diazocinliganden1 und 2, die beide mit violettem und grünem Lichtzwischenden E- undZ Konfigurationen geschaltet werden können. Die Selbstorganisationder vier Spezies(1-Z,1-E,2-Z,2-E) mit CoII-Ionen wurde nach Änderung der Koordinationsvektoren in Abhängigkeit von der Ligandenkonfiguration (Evs.Z) und dem Regioisomer (1vs.2) untersucht. Mit1-Zbildetsich Co2(1-Z)3, während mit 2-Z ein undefiniertes Gemisch verschiedener Spezies(Oligomere) beobachtet wurde. Bei Belichtung der E-Konfigurationen mit 385 nm wurde die gegenteilige Situation beobachtet, wobei 1-E Oligomere und 2-Eden KomplexCo2(2-E) 3 bildete.Der lichtgesteuerte Abbau/Aufbau wurdein einem Ligandenverdrängungsexperiment mit substöchiometrischen Mengen von CoII-Ionen demonstriert. Die abwechselnde Bestrahlung mit violettem undg rünem Licht führte zu einer reversiblen Umwandlung zwischenCo2(1-Z) 3 und Co2(2-E) 3 übermehrere Zyklen hinweg ohne signifikante Ermüdung

Tetrakis(diisopropyl amide) substituted norbornadiene and quadricyclane are highly barium selective ligands

Tetrakis(diisopropyl amide) substituted norbornadiene and quadricyclane derivatives were investigated for their extraction and transport capabilities with alkaline earth metal cations. Both amides exhibited a remarkably high preference of Ba2+ over any other alkali metal or alkaline earth cation. The binding geometries were determined by quantum chemical DFT calculations

Coarctate cyclization reactions: a primer

The cleavage of five-membered heterocycles possessing an exocyclic carbene or nitrene to form conjugated ene–ene–yne systems has been documented for over 40 years; however, the reverse reaction, using a conjugated “ene–ene–yne” precursor to form a heterocycle is a relatively new approach. Over the past decade, the Haley and Herges groups have studied computationally and experimentally the cyclization of the “hetero-ene–ene–yne” motif via an unusual class of concerted reactions known as coarctate reactions. This feature article details our synthetic and mechanistic work involving triazene–arene–alkynes and structurally-related systems to generate heterocycles using coarctate chemistry

Introducing a photo-switchable azo-functionality inside Cr-MIL-101-NH2 by covalent post-synthetic modification

For the first time an azo functionality was covalently introduced into a MOF by post-synthetic modi fi cation. The reaction of Cr-MIL-101-NH 2 with p-phenylazobenzoylchloride (1) and 4-(phenylazo)- phenylisocyanate (2) as the reactants led to the compounds Cr-MIL-101_amide and Cr-MIL-101_urea, with the azo groups protruding into the mesoporous cages. XRPD and N 2 sorption measurements con fi rm the intactness of the framework and the successful covalent modi fi cation was proven by IR- and NMR- spectroscopy. Furthermore, cis/trans isomerisation upon irradiation with light was demonstrated by UV/ Vis spectroscopy. More distinct changes in the UV/Vis spectra were observed for Cr-MIL-101_amide compared to Cr-MIL-101_urea, while the degree of functionalization, i.e. the number of reacted NH 2 -groups, seems to have a less pronounced effect. The variation of the sorption properties due to the cis/trans isomerisation was proven by methane adsorption measurements

The first porous MOF with photoswitchable linker molecules

We synthesized a porous twofold interpenetrated MOF [Zn 2 (NDC) 2 (1)] (coined CAU-5) using 3-azo-phenyl-4,4¢-bipyridine (1), 2,6-naphthalenedicarboxylic acid, and Zn(NO 3 ) 2 · 6H 2 O. The azo-functionality protrudes into the pores, and can be switched, by irradiation with UV light (365 nm), from the thermodynamically stable trans-isomer to the cis-isomer. Back-switching was achieved thermally and with an irradiation wavelength of l max = 440 nm