Studies aimed at elucidating factors involved in the control of chemoselectivity in single electron transfer promoted photoreactions of branched-polydonor substituted phthalimides

Factors that govern the chemical selectivities and efficiencies of SET-promoted photocyclization reactions of acceptor-polydonor substrates were explored by using systems comprised of phthalimide acceptors linked via polymethylene or polyethylenoxy chains to α-silylether and thioether donors. A number of linear and branched substrates of this type were prepared and their photochemical behavior was explored. The results of this effort have led to the identification of several key factors that govern the chemoselectivities and efficiencies of the competitive reaction pathways followed. The observations suggest that the length and nature of the chain linking the phthalimide acceptor and α-silyl donor sites are important factors in controlling the rates of formation of zwitterionic biradicals that serve as penultimate intermediates in routes for product formation. In addition, the rates of methanol promoted desilylation at cation radical centers in intermediate zwitterionic biradicals also play important roles especially in cases where chain length/type is not a factor. The results are discussed in terms of both their mechanistic and synthetic significance.