title: Single electron transfer-promoted photocyclization reactions of linked acceptor-polydonor systems: effects of chain length and type on the efficiencies of macrocyclic ring-forming photoreactions of tethered alpha-silyl ether phthalimide substrates.
abstract: Results of an investigation, aimed at gaining information about the factors governing the efficiencies of single electron transfer (SET)-promoted photocyclization reactions of linked acceptor-polydonor systems, are described. One set of substrates used in this effort includes alpha-trimethylsilyl ether terminated, polymethylene- and polyethylenoxy-tethered phthalimides and 2,3-naphthalimides. Photocyclization reactions of the polyethylenoxy-linked phthalimides and naphthalimides were observed to take place in higher chemical yields and with larger quantum efficiencies than those of analogs containing polymethylene tethers of near equal length. These findings show that the rates of formation of 1,omega-zwitterionic biradicals that serve as key intermediates in the photocyclization processes are enhanced in substances that contain oxygen donor sites in the chain. The findings suggest that these donor sites facilitate both initial SET to acceptor excited states and ensuing intrachain SET, resulting in migration of the cation radical center to the terminal alpha-trimethylsilyl ether position. In addition, an inverse relationship was observed between the quantum yields of photocyclization reactions of the tethered phthalimides and naphthalimides and the length of the polyethylenoxy chain. Finally, the roles played by chain type and length in governing photoreaction efficiencies were investigated by using intramolecular competition in photoreactions of polyethylenoxy and polymethylene bis-tethered phthalimides. Mechanistic interpretations and synthetic consequences of the observations made in this study are discussed.
authors.affiliation: Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National University, Busan 609-735, Korea.
authors.forename: Dae Won
authors.initials: DW
authors.lastname: Cho
authors.forename: Jung Hei
authors.initials: JH
authors.lastname: Choi
authors.forename: Sun Wha
authors.initials: SW
authors.lastname: Oh
authors.forename: Chunsheng
authors.initials: C
authors.lastname: Quan
authors.forename: Ung Chan
authors.initials: UC
authors.lastname: Yoon
authors.forename: Runtang
authors.initials: R
authors.lastname: Wang
authors.forename: Shaorong
authors.initials: S
authors.lastname: Yang
authors.forename: Patrick S
authors.initials: PS
authors.lastname: Mariano