PHOTOSENSITIZED ELECTRON-TRANSFER PROMOTED REDUCTIVE ACTIVATION OF CARBON-SELENIUM BONDS TO GENERATE CARBON-CENTERED RADICALS - APPLICATIONFOR UNIMOLECULAR GROUP-TRANSFER RADICAL REACTIONS

The investigation presented in this paper explores the mechanistic asp ects and synthetic potentials of photosensitized electron transfer (PE T) promoted reductive activation of organoselenium substrates. PET act ivation of substrates 1-5 is achieved through a photosystem comprised of light-absorbing 1,5-dimethoxynaphthalene (DMN) as electron donor an d ascorbic acid as co-oxidant. The fluorescence quenching of (1)DMN b y organoselenium compounds 1-5, correlation of fluorescence quenching rate constant with the reduction potentials of 1-5, and the dependence of photodissociation quantum yields of 1-5 on their concentration sug gests the occurrence of electron-transfer (ET) processes between (1)DM N and 1-5. Steady state photolysis of organoselenium substrates (R(2) CHSePh) in the presence of (1)DMN and ascorbic acid leads to the clea vage of the -C-Se-bond to produce a carbon-centered radical and PhSe(- ) species via the intermediacy of R(2)CH-SePh inverted left perpendicu lar (sic). The mechanistic interpretation for the reductive activation of -C-Se- bonds and the synthetic utility of observed cleavage patter n is extended for the unimolecular group transfer radical sequences.