Anthracene endoperoxide

However, even in the latter case (e.g., reaction of 1Oa + anthracene -> anthracene-endoperoxide), there seems to be no direct path from 1X to the stable endoperoxide, since all kinetic results have revealed the participation of two molecules of anthracene in the photooxygenation reaction. This also indicates that the excess energy, contained in 1X after transition from the F state, is used as kinetic energy with which 1S0 and 1Oa fly apart. 

Anthracene (404) and its derivatives are reported to yield 9,10-sndoperoxides (405). No mechanistic studies were made with respect to the influence of substituents and their positions on the reactivity of the anthracenes toward oxygen, except those discussed earlier. However, substituent effects have been observed with regard to the thermal stability of the anthracene endoperoxide and its thermal transformation reactions, which either lead to quinone formation or to evolution of oxygen and reformation of the hydrocarbon (Table XIII). 

Since 5,7,12,14-tetraphenylpentacene endoperoxide does not evolve molecular oxygen on heating, its structure, formerly assumed to be a 5,14-endoperoxide,286 was revised to be a 6,13-endoperoxide (409).267 On the same grounds, structure 411 was assigned to 9,10-diphenyl-tetracene endoperoxide.268 9,10-Diphenyl-ll,12-dichlorotetracene (412) is reported to yield a mixture of endoperoxides containing 20% of the 9,10-endoperoxide and 80% of the 11,12-endoperoxide (413 and 414, respectively).269 Recently, the structure of 9,10-diphenyl-l,4-dimethoxy-anthracene endoperoxide, formerly given as a 9,10-endoperoxide,270... 

Moreover, anthracene UV and IR bands decrease along the reaction because of an anthracene endoperoxide formation (Fig. lb,c). 

For example, irradiation of the anthracene endoperoxide 547 at / irr = 400 nm leads to the. svn-diepoxide 548 at low temperatures (Scheme 6.263). Upon heating, the product isomerizes to the benzocyclobutane derivative 549.1449... 

Reactive sy -h/s-epoxides available from the anthracene-endoperoxides by low-temperature irradiation at long wavelength could be thermally isomerized to benzocyclobutenic diethers and other products. A new kind of isomerization of aromatic endoperoxides, which is initiated by a Grob-fragmentation step, was described recently for anthracene and naphthalene bis-epoxides. The photochemistry of aromatic... 

As discussed in Chapter 2, triplet excited anthracene transfers its energy to oxygen to produce singlet excited oxygen OA,). The singlet oxygen in turn attacks a ground state anthracene to form a 9,10-endoperoxide. 

The amount of this endoperoxide produced depends upon the solvent and the anthracene concentration. 

The energy available from the anthracene triplet (42 kcal/mole) is sufficient to produce either of these states. The singlet excited molecule subsequently attacks a ground state anthracene to produce the observed endoperoxide. The 1Aff state is believed to be responsible for the addition to anthracene to form the endoperoxide since it closely resembles a diradical species, while the 1Ss+ state more closely resembles a dipolar ion. 

Those favoring the singlet oxygen mechanism (mechanism B) counter by asking why, if a mole-oxide is formed, must the oxygen be transferred to another anthracene to obtain a stable product <85) It would appear that if the intermediate has the structure shown below, that a single closure would produce the endoperoxide directly ... 

Oxygen Evolution from Endoperoxides of Substituted Anthracenes... 

The emission spectrum is similar to fluorescence of 9,10-diphenyl-l,4-tiinethoxy anthracene although it is not excited directly. The decomposition of the endoperoxide to (1) and (3) is the excitation producing step in wtcatalyzed cleavage and (2) is activated by energy transfer. The formation of 102 by elimination reaction is a very minor reaction step. 

Anthracene and its 9,10-disubstituted derivatives add singlet oxygen to form the 9,10-endoperoxide,825-827 but strong directing effect is displayed by substituents in the 1,4 positions 827... 

Evidence for adiabatic photolytic cycloreversions at room temperature has been obtained more frequently in recent years [121,122], The adiabatic generation of singlet oxygen by photochemical cycloreversion of the anthracene and 9,10-dimethylanthracene endoperoxides 105 and 106 proceeds with wavelength-dependent quantum yields of 0.22 and 0.35, respectively, and involves the second excited singlet state of the endoperoxides [123]. Photodissociation of the 1,4-endoperoxide from l,4-dimethyl-9,10-diphenylanthracene was found to yield both fragments, i.e., molecular oxygen and l,4-dimethyl-9,10-diphenylanthracene, in their electronically excited state [124]. 

The photooxide of naphthalene (74) on treatment with triphenylphosphine is converted to naphthalene 1,2-oxide (45).40 The photooxide of anthracene (75) is converted to syw-anthracene[4a,10 9,9a]diepoxide (76) in 78% yield by means of an interesting photochemical rearrangement.41 The endoperoxide of... 

The [4 + 2] cycloaddition to conjugated dienes or anthracenes to yield endoperoxides... 

In 2004, a report appeared that 9,10-dimethylanthracene-9,10-endoperoxide (48) arose from an electron-transfer photooxidation of 9,10-dimethylanthracene (38) with the use of the sensitizer Acr+-Mes in 02-saturated CH3CN at 0 °C [32]. Subsequent coupling of the anthracene radical cation and the superoxide ion generated endo-peroxide 48. Endoperoxide 48 was detected during the initial stage of the photooxidation, but was not isolated over time, the reaction yielded 10-hydroxanthrone, anthraquinone, and H202. 

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