Photochemistry of alkenes. 9. Medium-sized cycloalkenes

1985 ◽  
Vol 63 (7) ◽  
pp. 1845-1849 ◽  
Author(s):  
Paul J. Kropp ◽  
J. Derek Mason ◽  
Gardiner F. H. Smith
Keyword(s):  
Electron Transfer ◽  
Methyl Ether ◽  
Methanol Solution ◽  
Insertion Reactions ◽  
Superoxide Ion ◽  
Hydrogen Shift ◽  
Direct Irradiation ◽  
Nucleophilic Trapping ◽  
Π State ◽  
Cis Isomer

The behavior of the three medium-sized cycloalkenes cyclooctene (10), cyclodecene (17), and cyclododecene (21) on direct irradiation in pentane and methanol solution has been studied. The results are summarized in Tables 1–3. Irradiation of medium-sized cycloalkenes is a convenient procedure for the preparation of bicyclic products (cf. 13, 14, 19, 20, and 23) through transannular insertion reactions of carbene intermediates (cf. 11, 18, and 22) thought to arise from rearrangement of the 1[π,R(3s)] state via a 1,2-hydrogen shift. The formation of trans-decalin (20) is in contrast to the reported formation of the cis isomer on base-initiated decomposition of the corresponding tosylhydrazone. None of the three cycloalkenes 10, 17, or 21 underwent competing nucleophilic trapping of the 1[π,R(3s)] state in methanol, in contrast with other alkenes previously studied. However, cyclododecene (21) afforded the methyl ether 25, which apparently resulted from protonation of the 1(π,π*) state, and the epoxide 26, which is thought to arise from electron transfer to oxygen by the 1[π,R(3s)] state followed by protonation of the resulting superoxide ion and oxidation of unreacted cyclododecene (21).

Synthesis and Photocleavage of Quinoline Methyl Ethers: A Mild and Efficient Method for the Selective Protection and Deprotection of the Alcohol Functionality

2016 ◽  
Vol 69 (7) ◽  
pp. 763
Author(s):  
Anthony A. Provatas ◽  
Gary A. Epling ◽  
James D. Stuart
Keyword(s):  
Electron Transfer ◽  
Visible Light ◽  
Methyl Ether ◽  
Efficient Method ◽  
Substitution Reaction ◽  
Radical Scavenger ◽  
Single Electron Transfer ◽  
Radical Intermediate ◽  
Strong Base ◽  
Selective Protection

The synthesis and photocleavage of quinolinyl methyl ether-protected alcohols is reported in this study. A variety of quinoline methyl chlorides were synthesized, and protection of the various alcohols was performed via a substitution reaction in the presence of a strong base. Photocleavage of the quinolinyl methyl ether moiety proceeded under visible light with the formation of the charged quinolinyl radical intermediate through a single-electron transfer in the presence of a photosensitizer dye leading to the deprotected alcohol in excellent yields. The utility of triethylamine as a sacrificial reductant and d-sorbitol as a radical scavenger were also investigated in this study.

The high pressure photochemistry of alkenes. III. The 184.9 nm photoisomerization processes in acyclic alkenes

1985 ◽  
Vol 63 (7) ◽  
pp. 1424-1430 ◽  
Author(s):  
Guy J. Collin ◽  
Hélène Deslauriers
Keyword(s):  
Ground State ◽  
Internal Conversion ◽  
Rydberg State ◽  
Singlet State ◽  
Hydrogen Shift ◽  
Geometric Isomerization ◽  
Trans Isomerization ◽  
Show Evidence ◽  
Structural Isomerization ◽  
Π State

We have made a systematic study of the 184.9 nm photoisomerization of the gaseous acyclic alkenes. Apart from the cis-trans isomerization (geometric isomerization), we have also observed the formation of products arising from the 1,3-hydrogen and methylene shifts (structural isomerization). 1-Alkenes do not show evidence of structural isomerization. This kind of isomerization increases with an increase in the number of alkyl substituents around the double bond. These observations, combined with those from the literature, may be explained on the basis of the following: (a) the 1π,π* state is involved in the cis–trans isomerization process; (b) the 1π,R(3s) state is responsible for the methylene shifts; (c) another singlet state is required for the 1,3-hydrogen shift; (d) this last state is either at an energy level higher than that of the Rydberg state or the hot ground state. Finally, the photoexcited molecules, through internal conversion, may convert from one state to another, and their lifetime is long enough to be stabilized by collision.

The importance of conformation in the reactivity of radical cations. Changing configuration at saturated carbon centres

1992 ◽  
Vol 70 (1) ◽  
pp. 272-279 ◽  
Author(s):  
Allyson L. Perrott ◽  
Donald R. Arnold
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Molecular Mechanics ◽  
Radical Cation ◽  
Trans Isomer ◽  
Radical Cations ◽  
Singlet Excited State ◽  
Photostationary State ◽  
Configurational Isomerization ◽  
Cis Isomer

Irradiation of an acetonitrile solution of cis 1-methyl-2-phenylcyclopentane (1bcis); 1,4-dicyanobenzene (2), an electron-accepting photosensitizer; and 2,4,6-collidine (3), a nonnucleophilic base, leads to configurational isomerization of the cyclopentane; the photostationary state lies > 99% in favour of the trans isomer. The mechanism proposed for this reaction involves formation of the radical cation of 1bcis by photoinduced electron transfer to the singlet excited state of 2, deprotonation of the radical cation assisted by the base 3, reduction of the resulting benzylic radical by the radical anion [Formula: see text], and reprotonation of the benzylic anion to give both the cis and the trans isomers of 1b. The photostationary state is controlled by the relative rates of deprotonation of the radical cations of 1bcis and trans; these rates are dependent upon the extent of overlap of the SOMO of the radical cation, which is largely associated with the phenyl ring, and the benzylic carbon–hydrogen bond. Molecular mechanics calculations (MM3 and MMP2) are used to calculate the preferred conformations of the isomers. The required orbital overlap is 31% effective with the global minimum conformation of the cis isomer and essentially ineffective for the low-lying conformations of the trans isomer. This proposed mechanism is supported by Stem–Volmer quenching studies, which indicate that both isomers quench the singlet excited state of 2 at the diffusion-controlled rate, and by deuterium incorporation studies. When irradiation of the cis isomer is carried out in acetonitrile–methanol-O-d as solvent, isomerization is accompanied by deuterium exchange at the benzylic position; the trans isomer is stable under these conditions. Keywords: photosensitized electron transfer, radical cation, deprotonation, configurational isomerization, conformation, molecular mechanics (MM3).

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