Dioxetanes substitution

Dioxetanes substituted with anilines also undergo base-induced triggering. For example, it has been reported that treatment of 67 with Bu OK in DMSO produces the anion 68, which decomposes to emit red light via the CIEEL process (Scheme 17) <2005BCJ1899>. 

Several years ago it was noted that the behavior of dioxetanes substituted with large resonance groups (for example the dioxetanes postulated as intermediates in many bioluminescent reactions) is quite distinct from that of alkyl-, alkoxy-, or simple aryl-substituted dioxetanes (T. Wilson, 1976). The decomposition products of these dioxetanes are often highly fluorescent, possessing lowest excited ttti states, the yields of excited singlet states are often remarkably high, and the dioxetane stability is apparently low. It was suggested at that time that an alternative mechanism, perhaps a truly concerted mechanism, was operative. 

In recent years several new dioxetanes substituted with easily oxidized groups, notably various aminoaryl groups, have been prepared and studied. Also in recent years, the chemically initiated electron-exchange luminescence... 

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. 

In 1982, the Schaap group demonstrated that chemiluminescence can be induced by the addition of a base to dioxetanes bearing a phenolic substituent [11]. Herein, the same group presents a method utilizing aryl esterase to catalyze the cleavage of a naphthyl acetate-substituted dioxetane in aqueous buffer at ambient... 

Me Capra in particular proposed n> that the chemiluminescence reactions of a large number of organic compounds had this concerted dioxetane decomposition step as key reaction in the production of electronically excited products, namely acridinium salts 25,26,27) indolylperoxides 28>, activated oxalic esters 29>, diphenyl carbene 30>, tetrakis-dimethylamino-ethylene 31 32>, lucigenin 33>, and substituted imidazoles 23>. 

The oxazolidinone-substituted olefin Ic (Scheme 3) constitutes another fortunate substrate for the diastereoselective synthesis of a chiral dioxetane , which is of preparative value for the enantiomeric synthesis of 1,2 diols . For example, the photooxygenation of the enecarbamate Ic produces the asymmetric dioxetane 2c in >95% jt-facial diastereoselectivity. The attack of the O2 occurs from the jt face anti to the isopropyl... 

A noteworthy feature of the CIEEL phenomenon is the fact that the emission spectrum of the alkaline-phosphatase-triggered dioxetane m-15c coincides with that of the NaOH-triggered, hydroxy-substituted dioxetane m-15e in the absence of enzyme (Figure 4) . 

FIGURE 4. Normalized CIEEL spectmm of the alkaline-phosphatase-triggered ([alkaline phosphatase] = 2 x 10 M) dioxetane m-15c (1.7 x 10 M) in 0.05 M carbonate buffer (pH 9.5), and that of the NaOH-triggered, hydroxy-substituted dioxetane m-15c (3.4 x 10 M, pH 12.7), both at 20 °C. Reprinted with permission from Reference 34b. Copyright (2000) American Chemical Society... 

We have recently described a calibration procedure for the determination of excitation quantum yields on commercial fluorimeters, utilizing the luminol standard , and have thereby determined singlet excitation quantum yields for the peroxyoxalate reaction with bis(2,4,6-trichlorophenyl) oxalate (TCPO), hydrogen peroxide and imidazole, using various activators . The same calibration method has been utilized to determine the singlet quantum yields obtained in the induced decomposition of protected phenoxyl-substituted 1,2-dioxetanes 6 and and compared them to the well-investigated... 

The experimentally observed substituent effect on the triplet and singlet quantum yields in the complete series of methyl-substituted dioxetanes, as well as the predicted C—C and 0—0 bond strength for the four-membered peroxidic rings , have led to the hypothesis that a more concerted, almost synchronized, decomposition mechanism should lead to high excitation quantum yields (as in the case of tetramethyl-l,2-dioxetane), whereas the biradical pathway presumably leads to low quantum yields (as in the case of the unsubstituted 1,2-dioxetane)" . However, it appears that this criterion of concertedness is difficult to apply generally to structurally dissimilar dioxetane derivatives. 

Nevertheless, there are two highly efficient CL systems which are believed to involve the CIEEL mechanism in the chemiexcitation step, i.e. the peroxyoxalate reaction and the electron transfer initiated decomposition of properly substituted 1,2-dioxetanes (Table 1)17,26 We have recently confirmed the high quantum yields of the peroxyoxalate system and obtained experimental evidence for the validity of the CIEEL hypothesis as the excitation mechanism in this reaction. The catalyzed decomposition of protected phenoxyl-substituted 1,2-dioxetanes is believed to be initiated by an intramolecular electron transfer, analogously to the intermolecular CIEEL mechanism. Therefore, these two highly efficient systems demonstrate the feasibility of efficient excited-state formation by subsequent electron transfer, chemical transformation (cleavage) and back-electron transfer steps, as proposed in the CIEEL hypothesis. 

At low temperatures dioxetane adducts with trivalent phosphorus have been isolated by Bartlett and coworkers. These cyclic phosphoranes gradually decompose to give the corresponding epoxide and phosphine oxide (Scheme 39) (73JA6486). Aryl-substituted phosphines... 

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