title: Synthesis of 4-chalcogeno-1-aza-1,3-butadiene derivatives by intramolecular cyano-Diels-Alder reaction and borane-coordination-induced fluorescence enhancement.
abstract: 4-Thio-1-aza-1,3-butadiene derivatives 3 incorporating a rigid dibenzobarrelene skeleton were synthesized by the intramolecular cyano-Diels-Alder reaction of 9-anthryl cyanoethenyl sulfides 6. The thermal reaction of 6 afforded an equilibrium mixture of 3 and 6, but the cyclization was effectively promoted by the addition of BF3·Et2O or B(C6F5)3 to yield imine-borane adducts 8 and 9. The imine-borane adducts emit intense blue fluorescence both in solution and in the crystalline state. This is in stark contrast to free imines 3, which are weakly fluorescent. Selenium analogue 4 and N-oxide 12 of 3a were synthesized, along with their B(C6F5)3 adducts.
authors.affiliation: Department of Chemistry, Graduate School of Science and Engineering, Saitama University , 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Ishii
authors.forename: Yutaro
authors.initials: Y
authors.lastname: Aoki
authors.forename: Norio
authors.initials: N
authors.lastname: Nakata