Chemiluminescence in autoxidation of phosphonate carbanions. Phospha-1,2-dioxetanes as the most likely high-energy intermediates

Autoxidation of the phosphonate carbanions derived from 9-phosphono-10-hydroacridanes provided chemiluminescence ascribed to the excited acridone anion. The intramolecular CIEEL (chemically initiated electron exchange luminescence) mechanism can be applied to this chemiluminescence because of the much higher emission efficiency compared to that of 9-phosphono-10-methylacridanes. The effect of the phosphonate substituents on the emission efficiency and especially on the rates of the chemiluminescence decay can be interpreted to originate from the valence deviation of the phosphorus atoms, which is connected with the substituent effect on the geometrical selectivity in the olefination reaction of the phosphonate carbanions. The enhanced chemiluminescence in the presence of the fluorophores was also detected in autoxidation of the carbanions of diethyl diphenylmethylphosphonate and fluorenylphosphonate. Although the evidence is circumstantial, these results strongly support the belief that phospha-1,2-dioxetane is the most likely high-energy intermediate generating the excited molecules.     

1,2-dioxetanes as chemiluminescent intermediates in the triplet oxygen oxygenation of olefins.

Several enol ethers react in the dark at elevated temperatures with triplet oxygen, producing ketones and chemiluminescene. Other electron-rich olefins were investigated.     

Intramolecular charge-transfer-induced chemiluminescent decomposition of 1,2-dioxetanes bearing a phenylmethanide anion

Dioxetanes (1) bearing a phenyl moiety substituted with a methylene or methine having an electron-withdrawing group(s) (-CH₂-Ew or -CH(X)-Ew) and dioxetane (2) bearing a 3-(1-cyanoethenyl)phenyl group were synthesized. Treatment of dioxetanes (1) with tetrabutylammonium fluoride (TBAF) caused their decomposition with accompanying emission of light with maximum wavelength at 530-758 nm. The Michael addition of a bis(methoxycarbonyl)methanide anion to dioxetane (2) produced initially an unstable dioxetane bearing a phenylmethanide anion, decomposition of which gave light with maximum wavelength at 710-740 nm. Intramolecular cyclopropanation without decomposition of the dioxetane ring took place concurrently for the Michael reaction-induced decomposition of 2 with the bis(methoxycarbonyl)chloromethanide anion.     

Spiroadamantyl stabilization of sulfur-substituted 1,2-dioxetanes

With the help of spiroadamantyl substitution, the first sulfur-substituted 1,2-dioxetanes $\text{9}$ and $\text{10}$, respectively derived from thiophenylmethyleneadamantane ($\text{7}$) and 2-adamntylidene-1, 3-dithian ($\text{8}$) were prepared via singlet oxygenation and detected by NMR.     

Fluoride-induced chemiluminescent decomposition of 1,2-dioxetanes bearing a phenyl moiety substituted with a methyl having an electron-withdrawing group

A new type of dioxetane bearing a 3-(cyanomethyl)phenyl (1a), 3-(methoxycarbonylmethyl)phenyl (1b), 3-(benzoylmethyl)phenyl (1c), or 3-[cyano(methoxycarbonyl)methyl]phenyl group (1d) decomposed through an intermediary dioxetane bearing a benzylic carbanion to afford crimson to yellow light on treatment with TBAF in DMSO.     

Thermolysis of disubstituted 1,2-dioxetanes: Activation parameters and chemiexcitation yields

trans-3-Methyl-4-(p-anisyl)-1,2-dioxetane 1, trans-3-methyl-4-(o-anisyl)-1,2-dioxetane 2 , 3-methyl-3-benzyl-1,2-dioxetane 3 , and 3-methyl-3-p-methoxybenzyl-1,2-dioxetane 4 were synthesized in low yield by the β-bromo hydroperoxide method. The activation parameters were determined by the chemiluminescence method (for 1 ΔG≠ = 22.8 ± 0.3 kcal/mol, Δ≠ = 22.2, ΔS≠ = −1.7 e.u., k₆₀ = 7.6 × 10⁻³s⁻¹; for 2 ΔG≠ + 23.6 ± 0.3 kcal/mol, ΔH≠ = 22.8, ΔS≠ = −2.2 e.u., k₆₀ = 2.5 × 10⁻³S⁻¹; for 3 ΔG≠ = 24.0 ± 0.4 kcal/mol, ΔH≠ = 23.1, ΔS≠ = −2.7 e.u., k₆₀ = 1.2 × 10⁻³S⁻¹; for 4 ΔG≠ = 24.0 ± 0.2 kcal/mol, ΔH≠, = 23.2, ΔS≠, = −2.4 e.u., k₆₀ = 1.2 × 10⁻³s⁻¹). Thermolysis of 1–4 produced excited carbonyl fragments (direct production of high yields of triplets relative to excited singlets) [chemiexcitation yields ϕ^T, ϕ^S, respectively: for 1 0.02, 0.0001; for 2 0.02, 0.0001; for 3 0.03, 0.0002; for 4 0.02, 0.0001]. The effect of paramethoxyaryl substitution was consistent with electronic effects. The ortho substitution in 2 resulted in an increase in stability of the dioxetane, opposite that observed for an electronic effect. The results are discussed in relation to a diradical-like mechanism.     

X-ray structural parameters and the thermal stability of 1,2-dioxetanes

The structural parameters and thermal activation data for 1,2-dioxetanes are reported, showing that the degree of puckering of the peroxide ring does not influence the thermal stability of these “high energy” molecules.     

The sensitized photooxygenation of methyl substituted 1,2-diphenylcyclobutenes

A series of Me substituted 1,2-diphenylcyclobutenes was subjected to dye-sensitized photooxidanon in the presence ofmethylene blue. In the case of the 3,3-dimcthyl-, 3,3,4-tnmethyl- and 3,3,4,4tetramcthyl, 2-diphcnylcyclobutencs, the sensitized oxidations arc accompanied by ring-contraction with concomitant ortho hydroxylation of one aromatic nucleus. When electron transfer induced photooxidation techniques utilizing 9,10-dicyanoanthraccne (DCA) as a sensitizer are employed with the series of Me substituted diphcnykyclobutenes, the reactions take a markedly different course and a broad spectrum of oxidation products are obtained including, most notably, ozonides of the cyclobutencs. The mechanisms of these conversions are addressed and the significance of the results discussed.     

Effects of heteroatom substituents on the properties of 1,2-dioxetanes

Nitrogen and sulfur-substituted dioxetanes exhibit dramatically lower activation energies for decomposition compared to the corresponding oxygen-bearing dioxetane. A mechanism involving intramolecular electron-transfer processes is proposed for the cleavage of these unstable dioxetanes.     

Investigations on the thermal decomposition of 1,2-dioxetanes via DSC

Reproducible measurements, reliable results and 1^st order kinetics for the whole reaction are obtained during the thermal decomposition of dioxetanes only, if inclusions of impurities in commercial sample pans are blocked by additional thick (magnitude of 100 ?m) and close Al₂O₃ protective layers. As a rule, nearly the same activation parameters are then found both for the decomposition of solvent-free dioxetanes and diluted solutions in several solvents. Mixtures of different dioxetanes in the same solvent contribute independently to the overall heat flow rate.

     

Chemiluminescence of 1,2-dioxetanes,the photosensitized oxidation products of triallate

Conclusions Degradation of the triallate herbicide under the action of singlet oxygen proceeds through unstable 1,2-dioxetanes, the decomposition of which is accompanied by chemiluminescence and leads to formation of chloroanhydride and phosgene.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2016–2019, September, 1987.     

Chemical and enzymatic triggering of 1,2-dioxetanes. 2: fluoride-induced chemiluminescence from tert-butyldimethylsilyloxy-substituted dioxetanes

Thermally stable 1,2-dioxetanes bearing tert-butyldimethylsilyloxyaryl groups have been prepared. Reaction of these dioxetanes with fluoride ion at ambient temperature in MeCN and DMSO generates chemiluminescence with efficiencies up to 25%.     

Cidnp study of reactions of ketyls and dianions derived from benzophenone and fluorenone with acetic anhydride

A study is presented of ¹H and ¹³C CIDNP effects in the reactions of Na and Li salts of ketyls and dianions derived from benzophenone and fluorenone with acetic anhydride in tetrahydrofuran and dimethoxyethane. CIDNP effects were observed for products obtained by mixing of reactants both at high and at low field. Interpretation of the CIDNP effects (mixing at high field) indicates that in reactions of ketyls with acetic anhydride the primary step is O-acylation followed by spin-selective electron transfer between ketyl and O-acylated ketyl. At higher dilution or in the presence of strongly coordinating agents, heterolytic deprotonation of acetic anhydride by ketyl is also observed. CIDNP effects depend on the presence of ketyl which affects the relaxation of sterically accessible nuclei and also suppresses the intensity of ketone signals by rapid electron transfer. In reactions of dianions, electron transfer between dianion and acetic anhydride partly takes place, and the ketyl formed in this way reacts with a further molecule of acetic anhydride.     

Photochemical (2 + 2) cycloaddition of and thermal decomposition to n-methylacridone and acetone: chemiluminescence as a probe of possible formation of 1,2-dioxetanes

Irradiation of N-methylacridone (NMA) in an acetone solution at ?78°C in the argon atmosphere afforded light emission (φ_CL: 10^?6 - 10^?8 einstein/mol) upon warming-up to room temperature. The final products were NMA acetone exclusively.     

Remote functionalisation via sodium alkylamidozincate intermediates: access to unusual fluorenone and pyridyl ketone reactivity patterns

Treating fluorenone or 2-benzoylpyridine with the sodium zincate [(TMEDA)·Na(μ-(t)Bu)(μ-TMP)Zn((t)Bu)] in hexane solution, gives efficient (t)Bu addition across the respective organic substrate in a highly unusual 1,6-fashion, producing isolable organometallic intermediates which can be quenched and aerobically oxidised to give 3-tert-butyl-9H-fluoren-9-one and 2-benzoyl-5-tert-butylpyridine respectively.     

Remote substituent effects on the photooxygenation of 9,10-diarylanthracenes: strong evidence for polar intermediates

Two different reaction pathways in the photooxygenation of 9,10-diarylanthracenes are identified, with strong evidence for polar (forward, singlet oxygen addition) and radical (backward, thermolysis) intermediates.     

Formation of 1,2-dioxanes by electron-transfer photooxygenation of 1,1-disubstituted ethylenes

Electron-rich 1,1-diarylethylenes (1a–e) afford 3,3,6,6-tetraaryl-1,2-dioxanes (3a–e) in high yields (>907%) when subjected to electron-transfer photooxygenation in the presence of DCA. Whereas 1,1-diphenyl-ethylene (1f) and 1,1-di(p-chlorophenyl)ethylene (1h) yield the 1,2-dioxanes 3f and 3h at 30% and less than 10%, respectively, there is negligible (if any) 1,2-dioxane formation with 1,1-di(m-anisyl)ethylene (1i). 1,2-Dioxane formation proceeds in a chain reaction (Scheme 1). N-Vinylcarbazol (1g), however, yields the 1,2-dioxane 3g via the cyclobutane derivative 7 (Scheme 2).     

Thermolysis of 3-methyl-3-(o-aryl)-1,2-dioxetanes: Activation parameters and chemiexcitation yields

3-Methyl-3-(o-tolyl)-1,2-dioxetane 1 and 3-methyl-4-(o-bromophenyl)-1,2-dioxetane 2 were synthesized in low yield by the β-bromo hydroperoxide method. The activation parameters were determined by the chemilumin-escence method (for 1 ΔG^? = 24.7 ± 0.3 kcal/mol, ΔH^? = 25.4, ΔS^? = + 1.9 e.u., k₆₀ = 3.4 × 10^?4s^?1; for 2 ΔG^? = 24.7 ± 0.4 kcal/mol, ΔH^? = 24.7, ΔS^? = 0.0 e.u., k₆₀ = 4.1 × 10^?4s^?1). Thermolysis of 1–2 directly produced high yields of excited triplets as expected for this type of dioxetane [triplet chemiexcitation yields (?⁷) for 1 0.03; for 2 0.02; the ?^T/?^S ratios were estimated to be approximately 200 for both compounds]. The effect of ortho-aryl substituents was inconsistent with electronic effects. The ortho substitution in 1–2 resulted in a marked increase in stability of the dioxetanes. The results are discussed in relation to a diradical-like mechanism.     

Efficient trapping of the intermediates in the photooxygenation of sulfides by aryl selenides and selenoxides

Aryl selenides and selenoxides trap efficiently the intermediates in the reaction of singlet oxygen with sulfides. In the co-photooxygenation of 1 equiv of an aryl selenoxide with 1.3 equiv of dimethyl sulfide, the aryl selenone is formed quantitatively. Aryl selenides require 4-5 equiv of sulfide for their complete co-oxidation to selenones.