Radical ions in photochemistry. 6. The photosensitized (electron transfer) ring opening of aryloxiranes

1978 ◽  
Vol 56 (23) ◽  
pp. 2985-2993 ◽  
Author(s):  
Angelo Albini ◽  
Donald R. Arnold
Keyword(s):  
Electron Transfer ◽  
Ring Opening ◽  
Radical Anion ◽  
Electron Acceptors ◽  
Radical Ions ◽  
Subsequent Formation ◽  
Carbon Carbon Bond ◽  
Back Electron Transfer ◽  
Carbonyl Ylide ◽  
Cis And Trans

The photosensitized (electron transfer) irradiation of cis- and trans-2,3-diphenyloxirane (1 and 2) led to cleavage of the oxirane carbon–carbon bond and subsequent formation of the carbonyl ylide. The resulting carbonyl ylides have been trapped with the dipolarophiles, acrylonitrile, maleonitrile, and fumaronitrile. The resulting isomeric tetrahydrofuran derivatives have been characterized. Sensitizers (electron acceptors) which are effective include 1,4-dicyanonaphthalene, 1,4-dicyanobenzene, dimethyl terephthalate, and methyl 4-cyanobenzoate; 1-cyanonaphthalene was not effective. The proposed mechanism involves formation and cleavage of the oxirane radical cation followed by back electron transfer from the sensitizer radical anion to give the carbonyl ylide. Electrochemical and photophysical evidence which supports the proposed mechanism was obtained.

Radical ions in photochemistry. 18. The photosensitized (electron transfer) tautomerization of alkenes; the 1,1-diphenyl alkene system

1987 ◽  
Vol 65 (9) ◽  
pp. 2312-2314 ◽  
Author(s):  
Donald R. Arnold ◽  
Shelley A. Mines
Keyword(s):  
Hydrogen Bond ◽  
Electron Transfer ◽  
Radical Cation ◽  
Radical Anion ◽  
Relative Rate ◽  
Radical Cations ◽  
Radical Ions ◽  
Back Electron Transfer ◽  
Ambident Anion ◽  
Determining Factor

The photosensitized (electron transfer) irradiation of several conjugated 1,1-diphenyl alkenes, in acetonitrile with 1,4-dicyanobenzene or 1-cyanonapthalene as electron accepting sensitizer and 2,6-lutidine as base, leads essentially quantitatively to tautomerization to the less stable unconjugated isomer(s). The proposed mechanism for this reaction involves formation of the alkene radical cation and sensitizer radical anion followed by deprotonation of the radical cation, reduction of the resulting radical to the ambident anion by back electron transfer from the radical anion, and reprotonation. There are several steps in this mechanism that could control the ratio of isomers. Evidence is provided that, at least in some cases, it is the relative rate of deprotonation from the isomeric radical cations that is the determining factor. This rate is influenced by the conformation of the radical cation; the carbon–hydrogen bond involved in the deprotonation step must overlap with the singly occupied molecular orbital.

The effect of meta- or para-cyano substitution on the reactivity of the radical cations of arylalkenes and alkanes. Radical ions in photochemistry, Part 34

1995 ◽  
Vol 73 (3) ◽  
pp. 307-318 ◽  
Author(s):  
Donald R. Arnold ◽  
Xinyao Du ◽  
Jing Chen
Keyword(s):  
Electron Transfer ◽  
Molecular Orbital ◽  
Radical Cation ◽  
Radical Cations ◽  
Molecular Orbital Calculations ◽  
Single Electron Transfer ◽  
Radical Ions ◽  
Benzylic Carbon ◽  
Carbon Carbon Bond ◽  
Cis And Trans

The effect of electron-withdrawing substituents, meta- or para-cyano, on the reactivity of the radical cation of arylalkenes and alkanes has been determined. The radical cations were generated by single electron transfer (set) to an electron-accepting photosensitizer. Three reactions were studied: (i) the addition of nucleophile to the radical cation of arylalkenes, (ii) cleavage of the benzylic carbon–carbon bond of the radical cation of arylalkanes; and (iii) the deprotonation of the benzylic carbon–hydrogen bond of the radical cation of arylalkanes. The radical cations of 4-(1-phenylethenyl)benzonitrile (1b), 3-(1-phenylethenyl)benzonitrile (1c), 4-(2-methoxy-1-phenylethyl)benzonitrile (2b), 3-(2-methoxy-1-phenylethyl)benzonitrile (2c), cis- and trans-5-cyano-2-methoxy-1-phenylindane (6b-cis and -trans), and 6-cyano-3-phenylindene (7b) were generated, by single electron transfer to the lowest excited singlet state of 1,4-dicyanobenzene (3), in acetonitrile–methanol. The radical cations of 1b, 1c, and 7b react with methanol to yield the anti-Markovnikov adducts (2b, 2c, and 6b-cis and 6b-trans). The radical cations of 2b, 2c, and 6b-trans cleave at the benzylic carbon–carbon bond to give products derived from the radical and carbocation fragments. The radical cation of 6b-cis deprotonates from the benzylic position with subsequent formation of the diastereomer, 6b-trans. This behaviour can be explained/predicted on the basis of the proposed mechanisms for these reactions. Molecular orbital calculations (AM1) support the conclusions. Keywords: photosensitized, electron transfer, radical ions, radicals, molecular orbital calculations (AM1).

Competing Radical- and Anion-Mediated Pathways in the Reduction of Bridgehead Tosylates with Lithium Aluminium Hydride

1999 ◽  
Vol 52 (5) ◽  
pp. 367 ◽  
Author(s):  
Ernest W. Della ◽  
Wit K. Janowski
Keyword(s):  
Electron Transfer ◽  
Ring Opening ◽  
Radical Anion ◽  
Lithium Aluminium Hydride ◽  
Trans Isomers ◽  
Lithium Aluminium ◽  
Mechanism Of Reaction ◽  
Anion Transfer

Reaction of norborn-1-yl tosylate with lithium aluminium hydride in boiling tetrahydrofuran affords a mixture of norbornan-1-ol accompanied by the ring-opened products 4-methylcyclohexanol and 3-ethylcyclopentanol as their cis/trans isomers, as well as p-thiocresol and p-tolyl disulfide. Evidence strongly suggests that the reaction is mediated by the norborn-1-yloxy radical rather than the norborn-1-yloxy anion. The process is initiated by very slow acyl oxygen fission of the norbornyl tosylate, followed by reduction of the derived p-toluenesulfinate ion to give the p-thiocresoxide anion. Transfer of an electron from the latter to the substrate and decomposition of the derived norborn-1-yl tosylate radical anion leads to the norborn-1-yloxy radical which, upon ring opening, generates the monocyclic alcohols via the corresponding ketones. It is noteworthy that, when norborn-1-yl mesylate is exposed to lithium aluminium hydride, it yields norbornan-1-ol exclusively. In the absence of an efficient electron-transfer agent, the mechanism of reaction of norborn-1-yl mesylate is suggested to involve acyl oxygen fission only.

Radical anion ring opening reactions via photochemically induced electron transfer

1991 ◽  
Vol 32 (10) ◽  
pp. 1315-1316 ◽  
Author(s):  
J. Cossy ◽  
P. Aclinou ◽  
V. Bellosta ◽  
N. Furet ◽  
J. Baranne-Lafont ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Ring Opening ◽  
Radical Anion ◽  
Ring Opening Reactions

The effect of meta- and para-methoxy substitution on the reactivity of the radical cations of arylalkenes and alkanes. Radical ions in photochemistry. Part 26

1991 ◽  
Vol 69 (5) ◽  
pp. 839-852 ◽  
Author(s):  
Donald R. Arnold ◽  
Xinyao Du ◽  
Kerstin M. Henseleit
Keyword(s):  
Electron Transfer ◽  
Radical Cation ◽  
Bond Cleavage ◽  
Cation Radical ◽  
Radical Cations ◽  
Addition Product ◽  
Molecular Orbital Calculations ◽  
Carbon Carbon Bond ◽  
Markovnikov Addition ◽  
Cis And Trans

The effect of meta- and para-methoxy substitution on the reactivity of some radical cations has been determined. The compounds chosen for study were 1-(3-methoxyphenyl)-1-phenylethylene (7), 1-(4-methoxyphenyl)-1-phenylethylene (8), 3-(3-methoxyphenyl)indene (9), 3-(4-methoxyphenyl)indene (10), methyl 2-(3-methoxyphenyl)-2-phenylethyl ether (11), methyl 2-(4-methoxyphenyl)-2-phenylethyl ether (12), cis- and trans-2-methoxy-1-(3-methoxyphenyl)indane (13), and cis- and trans-2-methoxy-1-(4-methoxyphenyl)indane (14). The radical cations of these compounds were generated by photosensitization (electron transfer) using 1,4-dicyanobenzene (3) as the electron acceptor. The three reactions studied were: (1) The addition of nucleophiles (methanol) to the radical cation of the arylalkenes, a reaction that yields the anti-Markovnikov addition product. (2) The carbon–carbon bond cleavage of radical cations, which yields products derived from the radical and carbocation fragments. (3) The deprotonation of the radical cation, a reaction that can be used to invert the configuration at a saturated carbon centre. The mechanisms of these reactions are discussed and the factors that need to be considered in order to predict reactivity are defined. Molecular orbital calculations (UHF/STO-3G) were carried out on the radical cations of the model compounds 3- and 4-vinylanisole and 3- and 4-methylanisole. Key words: photochemistry, photosensitize (electron transfer), radical cation, radical.

Photo-driven electron transfer from the highly reducing excited state of naphthalene diimide radical anion to a CO2 reduction catalyst within a molecular triad

2017 ◽  
Vol 198 ◽  
pp. 235-249 ◽  
Author(s):  
Jose F. Martinez ◽  
Nathan T. La Porte ◽  
Catherine M. Mauck ◽  
Michael R. Wasielewski
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Metal Complex ◽  
Time Constant ◽  
Radical Anion ◽  
Oxidation Potential ◽  
Necessary Condition ◽  
Redox Potentials ◽  
Back Electron Transfer ◽  
Artificial Photosynthetic

The naphthalene-1,4:5,8-bis(dicarboximide) radical anion (NDI−˙), which is easily produced by mild chemical or electrochemical reduction (−0.5 V vs. SCE), can be photoexcited at wavelengths as long as 785 nm, and has an excited state (NDI−˙*) oxidation potential of −2.1 V vs. SCE, making it a very attractive choice for artificial photosynthetic systems that require powerful photoreductants, such as CO2 reduction catalysts. However, once an electron is transferred from NDI−˙* to an acceptor directly bound to it, a combination of strong electronic coupling and favorable free energy change frequently make the back electron transfer rapid. To mitigate this effect, we have designed a molecular triad system comprising an NDI−˙ chromophoric donor, a 9,10-diphenylanthracene (DPA) intermediate acceptor, and a Re(dmb)(CO)3 carbon dioxide reduction catalyst, where dmb is 4,4′-dimethyl-2,2′-bipyridine, as the terminal acceptor. Photoexcitation of NDI−˙ to NDI−˙* is followed by ultrafast reduction of DPA to DPA−˙, which then rapidly reduces the metal complex. The overall time constant for the forward electron transfer to reduce the metal complex is τ = 20.8 ps, while the time constant for back-electron transfer is six orders of magnitude longer, τ = 43.4 μs. Achieving long-lived, highly reduced states of these metal complexes is a necessary condition for their use as catalysts. The extremely long lifetime of the reduced metal complex is attributed to careful tuning of the redox potentials of the chromophore and intermediate acceptor. The NDI−˙–DPA fragment presents many attractive features for incorporation into other photoinduced electron transfer assemblies directed at the long-lived photosensitization of difficult-to-reduce catalytic centers.

1,n-Radical ions. The photosensitized (electron transfer) formation of 1,5-radical cations

1987 ◽  
Vol 65 (12) ◽  
pp. 2734-2743 ◽  
Author(s):  
Donald R. Arnold ◽  
Brian J. Fahie ◽  
Laurie J. Lamont ◽  
Jacek Wierzchowski ◽  
Kent M. Young
Keyword(s):  
Electron Transfer ◽  
Radical Cation ◽  
Phenyl Ring ◽  
Bond Cleavage ◽  
Relative Rate ◽  
Radical Cations ◽  
Carbon Bond ◽  
Trans Isomerization ◽  
Carbon Carbon Bond ◽  
Cis And Trans

The photosensitized (electron transfer) reactions of 3-phenyl-2,3-dihydrobenzofuran (8a), 5-methyl-3-phenyl-2,3-dihydrobenzofuran (8b), cis and trans-2-methoxy-1-phenylindane (9, cis and trans), 3,3-diphenyltetrahydrofuran (10), and 2,2-diphenyl-1-methoxycyclopentane (11) have been studied using 1,4-dicyanobenzene as an electron-accepting photosensitizer and acetonitrile–methanol (3:1) as solvent. These reaction conditions cause carbon–carbon bond cleavage of analogous acyclic β,β-diphenylethyl ethers to give products derived from the diphenylmethyl radical and the α-oxycarbocation intermediates. The purpose of this study was to determine if this reaction could be applied to five-membered cyclic derivatives to give 1,5-radical cations.The primary products from 8a and 8b were the dehydrogenated, aromatized 3-phenylbenzofurans 14a and 14b. These products react further; continued irradiation gave the methanol adducts, cis and trans-2-methoxy-3-phenyl-2,3-dihydrobenzofuran (15a and 15b, cis and trans). The only observed reaction of the indanes (9, cis and trans) was cis-trans isomerization. Deuterium was incorporated at the bis-benzylic position of 8 and 9 when the irradiation was carried out in acetonitrilemethanol-O-d. These results are consistent with reversible deprotonation from the radical cations. There was no evidence for carbon–carbon bond cleavage with either 8 or 9. The relative rate, deprotonation faster than carbon–carbon bond cleavage, is explained in terms of the conformation of the bond that cleaves in relation to the singly occupied molecular orbital (SOMO) of the radical cation. Oxidation potential measurements support the conclusion that the SOMO of 8 and 9 is largely associated with the fused phenyl ring and is therefore orthogonal to the benzylic carbon–carbon bond. Irradiation of cis or trans-2-methoxy-3-phenyl-2,3-dihydrobenzofuran (15a, cis or trans), under these conditions, leads to cis–trans isomerization. The mechanism in this case involves the reversible loss of methanol. There is evidence that the addition of methanol to 14 involves the sensitizer radical anion – 14 radical cation pair.In contrast with the fused bicyclic systems, the monocyclic tetrahydrofuran 10 and the methoxycyclopentane 11 both cleave under these conditions; the products are the expected acetals 22 and 29 formed from the intermediate 1,5-radical cations. In 10 and 11 the SOMO, which is largely associated with the diphenylmethyl moiety, can overlap with the adjacent carbon–carbon bond and cleavage occurs as in analogous acyclic systems. Both 10 and 11 are relatively stable to irradiation under conditions that are identical except with acetonitrile as solvent (without methanol). We found no evidence for cyclization of the intermediates (1,5-radical cation or 1,5-diradical) into the terminal phenyl ring.

Regioselective Dye-Induced Photocleavage of Epoxides as an Alternative Mild Synthetic Route to a Targeted Alcohol Functionality

2015 ◽  
Vol 68 (3) ◽  
pp. 500 ◽  
Author(s):  
Anthony A. Provatas ◽  
Gary A. Epling ◽  
James D. Stuart ◽  
Aliaksandr Yeudakimau
Keyword(s):  
Electron Transfer ◽  
Visible Light ◽  
Ring Opening ◽  
Radical Anion ◽  
Transfer Reaction ◽  
Electron Transfer Reaction ◽  
Hydroxyl Group ◽  
Synthetic Approach ◽  
Synthetic Route ◽  
Toxic Dyes

The regioselective cleavage of epoxides using visible light and a catalytic dye is reported in this study as an alternative mild synthetic approach. The epoxide radical anion is generated via visible light in an electron transfer reaction, induced by non-toxic dyes, leading to ring opening and formation of the corresponding alcohol with the hydroxyl group on the less substituted carbon in excellent yields.

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