Bicyclic dioxetanes

Recently, the synthesis has been reported of the novel bicyclic dioxetanes 22a-c , which possess a remarkable chemiluminescence efficiency in aqueous media. Of the dioxetanes 22a-c with the 3-hydroxy-4-isoxazolylphenyl functionality, the derivative 22a is the most suitable On triggering by NaOH in water, the dioxetane 22a displays the highest CIEEL yield (0.24 at 25 °C), whereas the efficiency of componnds 22b and 22c is much lower (0.064 and 0.015, respectively). Nevertheless, the latter are still snfficiently efficient triggerable dioxetanes and quite adequate for their use in aqneons media. Snch unprecedented results definitely merit further exploration. 

SOLVENT-PROMOTED CHEMILUMINESCENT DECOMPOSITION OF BICYCLIC DIOXETANES BEARING A 4-(BENZOTHIAZOL-2-YL)-3- HYDROXYPHENYL... 

Matsumoto M, Akimoto T, Matsumoto Y, Watanabe N. Bicyclic dioxetanes bearing a 4-(benzoazol-2-yl)-3-hydroxyphenyl moiety chemiluminescence profile for base-induced decomposition in aprotic medium and in aqueous medium. Tetrahedron Lett 2005 46 6075-8. 

ALKALINE METAL ION ENHANCED CHEMILUMINESCENCE OF BICYCLIC DIOXETANES BEARING A 3-HYDROXYNAPHTHALEN-2-YL GROUP... 

Fig. 4. Bicyclic dioxetanes bearing a 3-hydroxyphenyl 4 or 7-hydroxynaphthalen-2-yl group 5...

In conclusion, we have discovered that chelation with alkaline metal ion, especially Li+, enhances markedly chemiluminescence efficiency of CTICL for an even pattern hydroxyaryl-substituted dioxetane, i.e., bicyclic dioxetane bearing a 3-hydroxynaphthalene-2-yl group 1 in THF. 

Hoshiya N, Fukuda N, Maeda H, Watanabe N, Matsumoto M. Synthesis and fluoride-induced chemiluminescent decomposition of bicyclic dioxetanes substituted with a 2-hydroxynaphthyl group. Tetrahedron 2006 62 5808-20. 

Hoshiya N, Watanabe N, Ijuin HK, Matsumoto M. Effect of intramolecular hydrogen bonding on thermolysis of dioxetane unusual instability of bicyclic dioxetanes bearing a hydroxynaphthyl group with vicinal substitution pattern. Chem Lett 2007 36 516-7. 

The conversion of small rings to smaller ones, without loss, is not common. 3-Chloroazetidine isomerizes reversibly to 2-chloromethylaziridine (Section 5.09.2.2.5). Flash vacuum pyrolysis can convert isoxazoles to azirines (Section 5.04.4.3). More common is the isomerization of medium-sized, i.e. five- or six-membered rings, e.g. certain succinimides (Scheme 23) (81JOC27) to azetidinediones, or bicyclic 1,2-dioxetanes to bis-oxiranes (Section 5.05.4.3.2). 

Photooxygenation of bicyclic enol ether 617 at —78°C affords intermediate 1,2-dioxetane 618, which reacts with a premixed acetaldehyde without acidic additives or... 

Figure 2 displays the CIEEL spectra of the monocyclic (m-15a) and bicyclic (m-15b) dioxetanes and the fluorescence spectra of the corresponding methyl m-oxybenzoate ions m-17a and m-17b, generated by the electron-transfer-induced cleavage of these dioxetanes . The coincidence of the fluorescence and the CIEEL spectra (Figure 2) conspicuously demonstrates that in both cases the same methyl m-oxybenzoate chromophore... 

FIGURE 3. Pertinent molecular orbitals for the electronic excitation by the CIEEL process of the crossed-conjugated oxyanions m-17a and m-17b derived from the monocychc (m-15a) and bicyclic (m-15b) dioxetane, as calculated by the AMI method. Reprinted with permission from Reference 34b. Copyright (2000) American Chemical Society... 

Hydrolysis of dioxetane 223, or of ketal 10, led to an inseparable mixture of expected product 225, as well as bicyclic isomer 226. The mixture was 1 2 (225 226), and underwent standard acylation reactions to give, for example, 179 on treatment with Ac20/pyridine/CH2Cl2. Carbonates such as 181 were available from 225 upon treatment with various chloroformates in pyridine/CH2Cl2. In other words, the alcohol 225 could be funneled away from the mixture by reaction with electrophiles, providing the desired tricyclic products. The bicyclic aldehyde 10 was isomerized to obtain tricyclic ketal 228 under dehydrating conditions in the presence of an alcohol. 

Among radical cations of n-donors we mention briefly those of 1,4-diazabicy-clo[2.2.2]-octane (99) and of the tricyclic tetraaza compound (100). For the bicyclic system a perfect correspondence has been reported between the AEs of the radical ion and the AIs of its precursor [276], The radical cation of the tetracyclic system, on the other hand, is significantly distorted. While the parent system has D2d symmetry and a b2 HOMO, the radical cation is distorted towards two equivalent structures of C2y symmetry (2E), with a two-center three-electron N — N bond [281, 282]. The dioxetane radical cations (101), invoked as intermediates in oxygenations via oxygen capture (Scheme 6), and characterized by ESR spectroscopy [8] contain analogous three-electron O—O bonds. 

The data displayed in Fig. 1 support the yh/Z-electron-transfer mechanism. To understand the process of the excited-state generation, the nature of the CIEEL emitter and the chemiexcitation mechanism need to be established. Fig. 2a displays the CIEEL spectra of the monocyclic (/n-la) and bicyclic (w-lb) dioxetanes and the fluorescence spectra of the meta-oxybenzoate ions derived from the electron-... 

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