Dioxetanes, photochemical reactions

Dioxetanes applications, 7, 484—485 electrophilic reactions, 7, 461 nucleophilic reactions, 7, 463-464 photochemical reactions, 7, 459 spectroscopy, 7, 455... 

For other photochemical reaction products from dioxetane decomposition, see Section X.). 

Energy transfer to photoreactive acceptors has also been widely utilized for excitation quantum yield determination (chemical titration), mainly in the decomposition of dioxetanes ° . The quantum yields are calculated from the photoproduct yield obtained at infinite energy acceptor concentrations ( = 1.0) by extrapolation of the double-reciprocal relationship between the photochemically active energy acceptor concentration and the photoproduct yield ( Lp ). H the quantum yield of the photochemical reaction (excitation quantum yield (< > ) can be calculated (equation 8) . ... 

Birks has recently prepared a monograph on chemluminescence and photochemical reaction detection in chromatography which is likely to be of particular interest to analytical chemists. Few papers on chemiluminescence have appeared in the mainstream chemical literature. A significant exception is a theoretical treatment of the mechanism of the chemiluminescent decompositon of 1,2-dioxetanes . A series of phenyl N-alkylacridinium 9-carboxylates have been synthesised and their chemiluminescent properties evaluated. ... 

In order to rationalize the complex reaction mixtures in these slurry reactions the authors suggested that irradiations of the oxygen CT complexes resulted in simultaneous formation of an epoxide and dioxetane36 (Fig. 34). The epoxide products were isolated only when pyridine was co-included in the zeolite during the reaction. Collapse of the 1,1-diarylethylene radical cation superoxide ion pair provides a reasonable explanation for the formation of the dioxetane, however, epoxide formation is more difficult to rationalize. However, we do point out that photochemical formation of oxygen atoms has previously been observed in other systems.141 All the other products were formed either thermally or photochemically from these two primary photoproducts (Fig. 34). The thermal (acid catalyzed) formation of 1,1-diphenylacetaldehyde from the epoxide during photooxygenation of 30 (Fig. 34) was independently verified by addition of an authentic sample of the epoxide to NaY. The formation of diphenylmethane in the reaction of 30 but not 31 is also consistent with the well-established facile (at 254 nm but not 366 or 420 nm) Norrish Type I... 

Voloshin AI, Shavaleev NM, Kazakov VP. Water enhances photoluminescence intensity of europium(III), terbium(III) and samarium(III) tris-P-diketonates in toluene solutions and chemiluminescence intensity of europium(III) and samarium(III) tris-P-diketonates in the reaction with dioxetane. J Photochem Photobiol A Chemistry 2000 136 203-8. 

However, in recent years, it has become apparent that several photoinduced oxidation reactions do not involve singlet oxygen as the reactive intermediate, and, consequently, the reaction products cannot be accounted for the mechanisms shortly reported above. Moreover, since the first report on the photochemical stereospecific synthesis of the most fascinating peroxide derivatives, i.e., 1,2-dioxetanes [32], it clearly appeared, with a few notable exceptions [33,38], that only electron-rich olefins, such as enamines, enol ethers, and thio-substituted... 

As was noted in Scheme 12, distonic radical cations obtained from cyclopropane bond cleavages add oxygen rapidly, producing products with two CO bonds. So do some alkene radical cations. Addition of O2 to an alkene radical cation is formally a nucleophilic attack by the single alkene n electron on O2, and oxidizes both carbon atoms (an alkene radical cations has formally two -f carbons, and the adduct a 1+ and an oxygen-bound carbon). The oxygenation of the radical cation of bia-damantylidine (96) leads to dioxetanes such as 98 in chain reactions (see Scheme 21) [110]. The reactions may be initiated electrochemically or photochemically, but tris(o,p-dibromophenyl)amine hexafluoroantimonate, 97, is a superior catalyst for the dark reaction of certain tetraalkylalkenes, with turnovers up to ca. 800 at... 

A number of theoretical studies have appeared on the mechanism of the oxirane-forming reaction of olefins and 0( P). A kinetic investigation of the reaction of oxirane and the 0( P) atom has shown that H-abstraction occurs rather than insertion to form a dioxetane intermediate, The thermal and photochemical epoxidation of propylene in the presence of sulfur dioxide and acetonitrile have been reported. ... 

Kazakov VP, Voloshin AI, Shavaleev NM. Chemiluminescence in visible and infrared spectral regions and quantum chain reactions upon thermal and photochemical decomposition of adamantylidenadamantane-l,2-dioxetane in presence of chelates of Pr(dpm)3 and Pr(fod)3. J Photochem Photobiol, A-Chem 1998 119 117-23. 

The reaction of singlet oxygen with 2,3-disubstituted indoles yields labile dioxetanes but these are partially stabilized if the indole has an iV-acyl substituent (93JOC47) and the products (e.g. 41, R = Me, = Bu ) may then be isolated. Reduction of the dioxetane (41) with dimethyl sulfide gives the epoxide (42). The dioxetane (43) is photochemically decomposed with intense luminescence (93TL5247). 

In the case of an enol ether derivative (eq 5), reaction with triethylsilyl hydrotrioxide produced an intermediate dioxetane which was cleaved to give 3-phenylpropionaldehyde upon warming. In contrast, reaction of the same enol ether with photochem-ically generated singlet oxygen proceeded via an ene pathway. After hydrolysis, this gave an a , -unsaturated aldehyde in 37% yield. ... 

Imino-l,2-dioxetans, which have been synthesized independently by several groups of workers, are available by reaction of ketenimines and singlet oxygen in one step. The dioxetans may be decomposed by photochemical means to give the expected ketones and isocyanates. 

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