title: Azahelicenes from the Oxidative Photocyclization of Boron Hydroxamate Complexes.
abstract: Aromatic hydroxamic acids (Ar-CO-NOH-Ar') were used as bidentate chelating ligands to generate the corresponding boron hydroxamate complexes, which were subsequently transformed into nitrogen-containing helicenes (azahelicenes) using an oxidative photocyclization method that is frequently used for stilbene-type (Ar-CH=CH-Ar') precursors of carbohelicenes. The nitrogen atom of the hydroxamate linker was thus directly embedded into the helicene core without using nitrogen-containing aromatic rings in the stilbene-type precursors. In a batch photoreaction, aza[4]helicenes were readily and efficiently prepared, but aza[6]helicenes underwent severe decomposition upon irradiation. Alternatively, a continuous flow photoreactor was employed to furnish an amide-type aza[6]helicene.
authors.affiliation: Department of Material and Biological Chemistry, Faculty of Science, Yamagata University, 1-4-12 Kojirakawa-machi, Yamagata-shi, Yamagata, 990-8560, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Murase
authors.affiliation: Department of Material and Biological Chemistry, Faculty of Science, Yamagata University, 1-4-12 Kojirakawa-machi, Yamagata-shi, Yamagata, 990-8560, Japan.
authors.forename: Toru
authors.initials: T
authors.lastname: Suto
authors.affiliation: Department of Material and Biological Chemistry, Faculty of Science, Yamagata University, 1-4-12 Kojirakawa-machi, Yamagata-shi, Yamagata, 990-8560, Japan.
authors.forename: Honoka
authors.initials: H
authors.lastname: Suzuki
keywords: continuous flow; helical structures; helicenes; hydroxamic acids; photocyclization