Electron dicyanoanthracene

I. The cleavage of a methylamine can be accomplished photochemically in the presence of an electron acceptor such as 9,10-dicyanoanthracene. ... 

Similarly, the reaction of photoexcited 9,10-dicyanoanthracene (DCA) with a benzylstannane yields the contact ion pair in which the cation radical undergoes rapid mesolytic cleavage of the C—Sn bond to afford benzyl radical and tributyltin cation (which then adds to DCA- )77 (Scheme 14). When such unimolecular processes are faster than the energy-wasting back electron transfer (/cbet) within the contact ion pair, the D/A reactions occur rapidly despite unfavorable driving forces for electron transfer. 

The photooxidation of tertiary methylamines sensitized by electron acceptors such as 9,10-dicyanoanthracene in the presence of lithium perchlorate results in demethylation thus tropinone yields nortropinone257. Photoinduced cyanation of tertiary amines with oxygen, a sensitizer and trimethylsilyl cyanide results in a-cyano nitriles (equation 88)258. 

The photosensitized electron transfer by 9,10-dicyanoanthracene (DCA) has been shown to initiate the addition of the a-silyl amine 44 to 4,4-dimethylcyclohexenone47 (equation 14). Intramolecular addition of a-silyl amine 45 was also shown to be feasible45,46 (equation 15). The primary step is electron transfer to give the aminium... 

The photo-oxidation of the aryl-substituted cycloheptatrienes 7-(/ -methoxy-phenyl)cycloheptatriene and 7-, 1- and 3-(/ -dimethylaminophenyl)cycloheptatrienes to the corresponding radical cations in de-aerated acetonitrile solution was accomplished by electron transfer to the electronically excited acceptors 9,10-dicyanoanthracene, iV-methylquinolinium perchlorate, iV-methylacridinium perchlorate and l,T-dimethyl-4,4-bipyridinium dichloride. In the case of l- p-methoxyphenyl)cycloheptatriene (62), deprotonation of the radical cation occurs successfully, compared with back electron transfer, to give a cycloheptatrienyl radical (63) which undergoes a self-reaction forming a bitropyl. If the photooxidation is done in air-saturated acetonitrile solution containing HBF4 and one of the acceptors, the tropylium cation is formed. Back electron transfer dominates in the / -dimethylaminocycloheptatrienes and the formation of the cycloheptatrienyl radical is prevented. 

Electron-transfer catalytic cycles with oxygen were also discovered in photochemical reactions with participation of an excited sensibilizer (9,10-dicyanoanthracene [DCNA]) and stilbene. The sensitizer assists an electron transfer from the substrate to oxygen. Oxygen transforms into the superoxide ion. Stilbene turns into benzaldehyde. In the absence of the sensitizer, this reaction does not take place even on photoirradiation (when oxygen exists in the first singlet state). In the singlet state,... 

Considering salt-cage effect interplay, it is necessary to go into a possibility of suppressing back-electron transfer during the formation of ion-radicals. One of the most prominent manifestation of this interplay consists in the oxidation of 1,2-diarylcyclopropane (DACP) with oxygen in the presence of photoexcited 9,10-dicyanoanthracene (DCNA) in acetonitrile (Mizuno et al. 1987) (Scheme 5.23). 

Nakamura and co-workers provided detailed mechanistic information for the photoinduced electron transfer from tri-1 -naphthyl phosphate and related compounds to 9,10-dicyanoanthracene yielding binaphthyls The intramolecular nature of the reaction could be established by using laser flash photolysis experiments as well as fluorescence measurements [17],... 

To secure the efficiency of the one electron transfer, electron acceptors like 9,10-dicyanoanthracene (DCA) or quinones in conjunction with UV or visible light irradiation are commonly employed. Although photosensitized reactions are usually associated with a singlet excited state (equations 4 and 5), some processes of this type can occur thermally in the dark. 

Furthermore, the authors were the first to gamer evidence that the back electron-transfer (BET) from the CO2 anion-radical to the cation-radical of the ACT, leading to the formation of the activator s excited singlet state. The AG bet values were calculated on the basis of the CIEEL sequence (Scheme 44), so this finding contributes further to confirm this mechanism. However, data obtained on two less commonly used activators 9,10-dimethoxyanthracene and, particularly, 9,10-dicyanoanthracene do not fit into the correlations obtained for the other activators, implying that details of this mechanism still require clarification. A putative explanation for the fact that 9,10-dimethoxyanthracene and 9,10-dicyanoanthracene do not correlate as predicted by CIEEL is the involvement of an alternative pathway, in which CO2 cation radical and the anion radical of the activator are formed by initial electron transfer from the peroxide to the activator (Scheme 45). ... 

The 9,10-dicyanoanthracene sensitized irradiation of c/i-stilbene results in nearly quantitative isomerization (>98%) to the trans isomer with quantum yields greater than unity. Therefore, the isomerization was formulated as a free radical cation chain mechanism with two key features (1) rearrangement of the c/i-stilbene radical cation and (2) electron transfer from the unreacted cis-olefin to the rearranged (trans-) radical cation. 

Synthetic applications of both intermolecular5-6 and intramolecular7 PET initiated cyclodimerizations have been reported. Common electron acceptors (A) arc neutral compounds such as 1,4-dicyanobenzene, 1,4-dicyanonaphthalene or 9,10-dicyanoanthracene usually dissolved in polar solvents like acetonitrile, or arc cationic compounds such as methylacridinium hexafluorophosphate which is soluble in dichloromcthane. 

The anti-Markownlkov orientation of addition in the presence of electron-acceptor sensitizers applies also to intramolecular reaction, and 5,5-dipheny pent-4-en-1-ol gives a tetrahydrofuran (2.SI) when irradiated in solution with 9,10-dicyanoanthracene, whereas its thermal reaction under proton-acid catalysis leads to 2,2-diphenyltetrahydropyran by Markownikov addition. Sometimes an added sensitizer is not required, if the alkene itself can act as a good electron-donor or electron-acceptor, and this is likely to be the reason why 1-lo-methoxyphenyl)propene adds photochemically to acetic acid (2.52), whereas l-phenylpropene does not. 

C-C Cleavage in Epoxides. Radical cations generated by photoinduced electron transfer from epoxides (130) or aziridlnes (131) also ring open, giving oxidative products in the presence of oxygen. For example, dicyanoanthracene sensitizes the conversion of aryl epoxides to ozonides, eq. 48,... 

The indirect electron transfer sensitization reported earlier when biphenyl was present in dicyanoanthracene-sensitized epoxide openings also finds analogy in the sensitized oxygenation of a mixture of trans-stilbene and tetraphenylethylene, eq. 76 (233) ... 

Electron transfer may also dominate the excited state chemistry of open shell radical ions. The fluorescence of the radical anions of anthraquinone and 9,10-dicyanoanthracene and the radical cation of thianthrene are quenched by electron acceptors and donors, respectively, although detailed kinetic analysis of the electron exchange do not correspond exactly either with Weller or Marcus theory (258). The use of excited radical cations as effective electron acceptors represents a... 

The photolysis of silanorbomadienes such as 344 sensitized by dicyanoanthracene (DCA) induced electron transfer and led to rearrangement affording the products 345, 346, and anthracene181 (equation 40). 

Silyl carbamates have recently been shown to undergo photoinduced electron transfer with substituted alkenes, in the presence of catalytic amounts of dicyanoanthracene and biphenyl (BP), to yield more complex carbamates182. Two examples which illustrate the complex structures created in good yield are shown in Scheme 61. 

A novel synthesis of 5,6-dihydro-4//-1,2-oxazincs (20) is presented via the photo-induced cyclization of y,<5-unsaturated oximes (21) see Scheme 4. Irradiation of (21) in the presence of 9,10-dicyanoanthracene (DCA) led to the heterocycle (20) only. The proposed mechanism proceeds via the radical cation (22), generated by single-electron transfer (SET) from the oxime (21) to the excited sensitizer (DCA. Cyclization of (22) affords the oxazine (20) after proton transfer to the DCA radical anion (DCA ) and H abstraction.61... 

From electrochemical studies it is known that an irreversible oxidation of C6o occurs at +1.76 V vs SCE in benzonitrile [165]. One of the first methods to generate the radical cation by radiation was performed by "/-irradiation of C6o in glass matrix at 77 K [166], A new absorption in the near IR at 980 nm was assigned to the C 6o (Fig. 19) [19]. Despite the sufficiently high reduction potential of +2.0 V of dicyanoanthracene, first attempts to generate the radical cation by photoinduced electron transfer were unsuccessful [Eq. (5)] [19]. One reason may be a fast back-electron transfer that competes with ionic dissociation in benzonitrile [19]. 

Mattay and coworkers extended the investigations of photoinduced electron tansfer from C6o to excited sensitizers and cosensitizers (Scheme 4) [173-175], They used dicyanoanthracene (DCA), dicyanonaphthaline (DCN), A-methylacri-dinium hexafluorophosphate (MA+), and triphenylpyrylium tetrafluoroborate (Tpp+) as sensitizers. In the case of DCA, DCN, and MA+, the addition of a cosensitizer (biphenyl) was necessary to produce the fullerene radical cation in sufficiently high yields [175], Otherwise, fast back-electron transfer seems to be predominant. However, by using TPP+ the formation of Q,o could be detected by EPR measurements even in the absence of a cosensitizer. This can be explained by (1) the high reduction potential (Ejed = 2.53 V vs SCE) and (2) the neutral form of the reduced sensitizer (electron shift) [174-176], Nevertheless, no influence of the cosensitizer on the EPR signal was observed under irradiation [175],... 

As a first example, the photochemical synthesis of substituted 1,2-dihydro-[60]fullerenes will be discussed. These compounds can be synthesized by various photochemical reaction pathways. In the first one the radical cation Qo is involved in the reaction. In 1995, Schuster et al. reported the formation of C6o radical cations by photosensitized electron transfer that were trapped by alcohols and hydrocarbons to yield alkoxy or alkyl substituted fullerene monoadducts as major products [211], Whereas Foote et al. used N-methylacridinium hexafluorophos-phate NMA+ as a sensitizer and biphenyl as a cosensitizer [167], Schuster et al. used 1,4-dicyanoanthracene (DCA) as a sensitizer for the generation of C 6o- The... 

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