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A novel type of azoniahetarene, namely, benzo[

The reaction of sodium cyanate with benzo[ b]quinolizinium substrates at room temperature gave 3-hydroxy-4-pyridyl-isoquinoline derivatives in good yields. Presumably, the overall reaction proceeds through an ANRORC-type sequence, that is, addition of the nucleophile, ring opening, and ring closure. Preliminary photophysical investigation of the parent compound revealed a pronounced sensitivity of its emission properties toward solvent effects and the pH of the medium.

It is shown by photometric and fluorimetric analysis, along with supporting theoretical calculations, that hydroxy-substituted benzo[b]quinolizinium derivatives display the characteristic features of organic photoacids. Specifically, the experimental and theoretical results confirm the strong acidity of these compounds in the excited state (pKa* < 0). The combination of the prototropic properties of 8- and 9-hydroxybenzo[b]quinolizinium with the particular solvent–solute interactions of the excited acid and its conjugate base leads to a pronounced fluorosolvatochromism, hence the emission maxima shift from 468 nm (8-hydroxybenzo[b]quinolizinium) or 460 nm (9-hydroxybenzo[b]quinolizinium) in CH3CN to 507 and 553 nm in DMF, respectively. This novel type of photoacid represents several features that may be used for applications as water-soluble fluorescent probes or as a source for the photoinduced supply of acidity.

Regiospecific C–N photocyclization of mono- and bis-styryl-substituted N-heterocycles was investigated. We demonstrated that the C–N regiospecificity of the photoinduced electrocyclization is a general feature of ortho-styryl-substituted N-heterocycles comprising one and two nitrogen atoms. This phototransformation provides a straightforward synthesis of the pharmaceutically important benzo[c]quinolizinium cation and its aza-analogues. Noticeably, bis-styryl derivatives undergo only one-fold cyclization with the second styryl fragment remaining uninvolved in the cyclization process. Photocyclization products of monostyryl derivativatives intercalate into calf thymus DNA (ct DNA), whereas photocyclization products of bis-styryl derivativatives possess a mixed binding mechanism with ct DNA. The results can be used for development of novel DNA-targeting chemotherapeutics based on benzo[c]quinolizinium derivatives.

Silanediyl 2 (generated by thermolysis of cyclotrisilane 1) reacts with benzophenone, tetracyclone, and fluorenone to yield products, which may originate from highly reactive siloxiranes as intermediates. However, using adamantanone as ketone, stable siloxirane 24 is obtained. The interaction of 2 with benzophenone anil or 36 gives heterocyclic compounds 31 and 37, respectively. The involvement of silaziridines in these reactions, as well as in the reactions of 1 with 1,4-diaza-1,3-butadienes 41a and b, which yield the expected formal [4 + 1] cycloaddition products, remains questionable.

[reaction: see text] Four pH-sensitive fluorescence probes are presented which consist of an anthracene fluorophore and a pi-conjugated oxazoline, benzoxazole, or pyridine substituent. The protonation of the heterocycles increases their acceptor properties and results in significant red-shifts of the absorption and emission maxima of the anthracene chromophore. The comparison between 2-[2'-(6'-methoxyanthryl)]-4,4-dimethyl-2-oxazoline and 2-[2'-(anthryl)]-4,4-dimethyl-2-oxazoline reveals that the donor-acceptor substitution pattern of the fluorophore is not required to achieve a red shift upon protonation. The benzoxazole and pyridine substituents offer a particular advantage due to their persistence under acidic conditions. Thus, these compounds may be used as efficient pH-sensitive fluorescence switches. Nevertheless, the switching of benzoxazole 2c requires relatively strong acidic conditions. The anthrylpyridinium exhibits a red-shifted emission in chloroform; however, it is nonfluorescent in aqueous or alcoholic solution. Although the oxazoline is not persistent under permanent acidic conditions, this heterocycle may be useful as a substituent in fluorescence indicators since it may be used to detect acid concentrations of 10(-4)-10(-5) M, which are close to the biologically relevant range.

[reaction: see text] A chiral periodic mesoporous organosilica (ChiMO) was prepared, in which a 1,2-bis-(ureido)cyclohexyl linker (38 wt %) is introduced into the walls of the hybrid organic-inorganic material. This silica was used as a host for 11-formyl-12-methyldibenzobarrelene (2), and the stereoselectivity of the di-pi-methane rearrangement of 2 within this host-guest complex was studied. At low conversions, the only product was the corresponding dibenzosemibullvalene. An enantiomeric excess of 24% at 11% conversion was obtained using the ChiMO as host. These values compare well with those achieved using a system based on conventional faujasites (LiY and NaY) as hosts incorporating a chiral auxiliary. We tested S-phenylglycine, S-proline, S-camphanic acid, and S-mandelic acid as chiral auxiliaries. In contrast to the behavior of the ChiMO material, adsorption of dibenzobarrelene in purely siliceous mesoporous MCM-41 silica (3.2 nm pore size) containing ephedrine failed, a failure that can be explained as arising from the large internal silanol population and high hydrophilicity of the siliceous MCM-41 sample.