title: Facile photochemical synthesis of 5,10-disubstituted [5]helicenes by removing molecular orbital degeneracy.
abstract: Photocyclodehydrogenation is a key reaction to synthesize helicenes; however, because of overannulation, it is not applicable to the synthesis of [5]helicene. Introduction of a cyano group was found to remove the orbital degeneracy of the low-lying unoccupied MOs; consequently, the lowest excitation comprises a single transition involving the C2-antisymmetric MO. Therefore, the problematic overannulation can be effectively suppressed. Moreover, in combination with the Knoevenagel reaction, a one-pot synthesis of 5,10-dicyano[5]helicene with 67% yield was accomplished.
authors.affiliation: Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University , Katsura, Nishikyo-ku, Kyoto 615-8510, Japan.
authors.forename: Natsuki
authors.initials: N
authors.lastname: Ito
authors.forename: Takashi
authors.initials: T
authors.lastname: Hirose
authors.forename: Kenji
authors.initials: K
authors.lastname: Matsuda