title: Photosensitized Electron Transfer Promoted Reductive Activation of Carbon-Selenium Bonds To Generate Carbon-Centered Radicals: Application for Unimolecular Group Transfer Radical Reactions.
abstract: The investigation presented in this paper explores the mechanistic aspects and synthetic potentials of photosensitized electron transfer (PET) promoted reductive activation of organoselenium substrates. PET activation of substrates 1-5 is achieved through a photosystem comprised of light-absorbing 1,5-dimethoxynaphthalene (DMN) as electron donor and ascorbic acid as co-oxidant. The fluorescence quenching of (1)DMN by 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 suggests the occurrence of electron-transfer (ET) processes between (1)DMN and 1-5. Steady state photolysis of organoselenium substrates (R(2)CHSePh) in the presence of (1)DMN and ascorbic acid leads to the cleavage of the -C-Se- bond to produce a carbon-centered radical and PhSe(-) species via the intermediacy of R(2)CH-SePh&uprhbr;(-)(*). The mechanistic interpretation for the reductive activation of -C-Se- bonds and the synthetic utility of observed cleavage pattern is extended for the unimolecular group transfer radical sequences.
authors.affiliation: Division of Organic Chemistry (Synthesis), National Chemical Laboratory, Pune 411 008, India.
authors.forename: Ganesh
authors.initials: G
authors.lastname: Pandey
authors.forename: K. S.
authors.initials: KS
authors.lastname: Sesha Poleswara Rao
authors.forename: K. V. Nageshwar
authors.initials: KV
authors.lastname: Rao