ISSN:
0009-2940
Keywords:
Photo-electron transfer
;
Pyrylium salts
;
Cation-radical cycloadditions
;
Electron-transfer chain reactions
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Several pyrylium, thiapyrylium, and pyridinium salts have been synthesized and used as sensitizers for photochemically induced electron-transfer (PET) reactions. The salts have been tested in the mixed cycloaddition reactions of styrenes 9 with 1,3-cyclohexadiene (8) or 1,1'-dicyclohexenyl (23). In the case of the PET [4 + 2] cycloaddition of styrene (9a) to 1,3-cyclohexadiene (8), the reaction takes place via the cation radical of the diene. When chloroform instead of dichloromethane is used as the solvent, only [2 + 2] cycloaddition products are obtained. In contrast, if 1,3-cyclohexadiene (8) is replaced by 1,1'-dicyclohexenyl (23), the key step of the reaction seems to be the oxidation of styrene (9). The product ratios depend on the sensitizers used. If solvent-separated ion pairs are formed, styrene reacts as diene to give 1-cyclohexenyloctahydro-phenanthrene derivatives 28; cycloaddition via contact ion pairs leads to the Diels-Alder product with styrene acting as the dienophile.
Additional Material:
11 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cber.19931260726
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