PHOTOINDUCED ELECTRON-TRANSFER INITIATED ACTIVATION OF ORGANOSELENIUMSUBSTRATES AS CARBOCATION EQUIVALENTS - SEQUENTIAL ONE-POT SELENYLATION AND DESELENYLATION REACTION

The investigation presented in this paper explores the mechanistic asp ects and synthetic potentials of PET activation of organoselenium subs trates. Fluorescence quenching of (DCN)-D-1 by a number of organosele nium compounds (RCH(2)SeR', 1-4), correlation of the fluorescence quen ching rate constants with the oxidation potentials of 1-4, and the dep endence of photodissociation quantum yields of 1-4 on their concentrat ion suggests the occurrence of electron transfer processes between (DC N)-D-1 and 1-4. Steady-state photolysis of 1-4 in the presence of (DC N)-D-1 leads to the efficient one-electron oxidative heterolytic diss ociation of the carbon-selenium bond to produce the carbocation (RCH(2 )(+) or equivalent) and radical-centered selenium species (R'Se-.) via the intermediacy of cation-radical [(RCH(2)SeR')(+.)]. Nucleophilic a ssistance in the fragmentation of (RCH(2)SeR')(+.) by methanol has bee n suggested on the basis of products obtained from the control PET rea ction of neopentyl phenyl selenide (8). The synthetic utility of these findings has been demonstrated for the deselenylation (Table 4) as we ll as one-spot sequential selenylation-deselenylation (Table 5) reacti ons.