Radical ions in photochemistry. Sensitised (electron-transfer) photochemical reactions of some 1-phenylcycloalkenes in polar, nucleophilic solvents

Abstract

Irradiation of 1-phenylcyclopentene, 1-phenylcyclohexene, and 2-phenylnorbornene in methanol, acetic acid-dioxan, and aqueous acetonitrile solution, with methyl p-cyanobenzoate or 1-cyanonaphthalene as sensitiser (electron-transfer) , gives fair to good yields of the product resulting from anti-Markovnikov addition of the nucleophilic solvent to the olefin.DIRECT or triplet sensitised irradiation of phenyl cyclic olefins, 1-phenylcyclopentene (I), 1-phenylcyclohexene (11) , and 2-phenylnorbornene (111) , in polar nucleophilic solvents, can lead to mixtures of the reduced olefin, polymer, and the Markovnikov addition pr0ducts.l In contrast we find electron-transfer photosensitised excitation of these olefins is a synthetically useful reaction for preparing the alcohol, ethers, and esters expected from anti-Markovnikov addition.Irradiation (medium-pressure mercury vapour lamp, Pyrex filter, 10') of an aqueous acetonitrile solution of (I)and 1-cyanonaphthalene (XV)t gave cis-(IV; 15%) and trans-2-phenylcyclopentanol (V; 27%). 2 From g.1.c. of the crude reaction mixture we estimated that <5y0 of any other adduct was present. When a similar irradiation was t The sensitiser was usually recovered ; however, in some cases (XV) was partially consumed to give l-cyano-3,4-dihydronaphthalene.$ New compounds (VI), (VII), (XIII), and XIV) gave satisfactory analysis or exact molecular weight for the parent-peak in the This is an expected product from (XV):. mass spectra. The structure of known compounds was confirmed by direct comparison (i.r.).

Direct Catalytic Anti-Markovnikov Addition of Carboxylic Acids to Alkenes

“…In seminal work, Arnold 8 and Gassman 9 have each reported single examples of anti-Markovnikov additions of acetic acid to alkenes employing stoichiometric quantities of single electron photooxidants. Despite the use of acetic acid as solvent, single regioisomers of the hydroacetoxylation adducts were obtained, albeit in modest yields.…”

Addition and cycloaddition reactions via photoinduced electron transfer

“…Arnold and his coworkers reported that the photoaddition of methanol to 1,1-diphenylethene occurs in the presence of methyl p-cyano-benzoate in an antiMarkownikoff manner [33]. Photoaddition of nucleophiles such as water, alcohols, acetic acid, and cyanide anion to electron-rich arylalkenes were also reported [34][35][36][37]. The photoaddition reaction proceeds via the mechanism as shown in Scheme 6.…”

Synthetic Aspects of Photochemical Electron Transfer Reactions

“…It is noteworthy that the corresponding neutral systems in methanol, ether, or cyclohexane, generate the same or similar radicals when irradiated through mechanisms which most likely involve hydrogen atom abstraction. Flash photolysis studies by Kosower(293) with l-ethyl-4-carboethoxypyridinium iodide 401 and by Cozzens(294) with I-methylpyridinium, I-methylcollidinium, and I-methylquinolinium io-dides have shown that these systems undergo intramolecular electron transfer generating iodine atoms and the corresponding heterocyclic radicals [e.g., 402, equation (49) (50) Charge transfer complexes which arise via single-electron transfer are also reported to be responsible for the fluorescence quenching of N-methylacridinium cation by various negatively charged counter ions. (295) Similarly, fluorescence quenching involving electron transfer in pyridinium salts has also been reported by McCall and Whitten.…”