title: Inverse electron-demand 1,3-dipolar cycloaddition of nitrile oxide with common nitriles leading to 3-functionalized 1,2,4-oxadiazoles.
abstract: A carbamoyl-substituted nitrile oxide was generated upon treatment of easily available 2-methyl-4-nitro-3-isoxazolin-5(2H)-one with THF (not dried); the reaction proceeded efficiently even in the absence of any special reagents and reaction conditions. The nitrile oxide caused 1,3-dipolar cycloaddition with common aliphatic nitriles or electron-rich aromatic nitriles to afford 3-functionalized 1,2,4-oxadiazoles, which are expected to serve as precursors for the preparation of a variety of functional materials by the chemical transformation of the carbamoyl group. While conventional preparative methods for 1,2,4-oxadiazoles involve the cycloaddition of an electron-rich nitrile oxide with an electron-deficient nitrile or a nitrile activated by a Lewis acid, our method employs the complementary combination of an electron-rich nitrile and an electron-deficient nitrile oxide- the inverse electron-demand 1,3-cycloaddition. The DFT calculations using B3LYP 6-31G* supported the abovementioned inverse reactivity, and also suggested the presence of an accelerating effect by the carbamoyl group as a result of hydrogen bond formation with a dipolarophilic nitrile.
authors.affiliation: School of Environmental Science and Engineering, Kochi University of Technology, Tosayamada Kami, Kochi, 782-8502, Japan. nishiwaki.nagatoshi@kochi-tech.ac.jp
authors.forename: Nagatoshi
authors.initials: N
authors.lastname: Nishiwaki
authors.forename: Kazuya
authors.initials: K
authors.lastname: Kobiro
authors.forename: Shotaro
authors.initials: S
authors.lastname: Hirao
authors.forename: Jun
authors.initials: J
authors.lastname: Sawayama
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Saigo
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Ise
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Okajima
authors.forename: Masahiro
authors.initials: M
authors.lastname: Ariga
mesh_terms: D003500:Cyclization; D004583:Electrons; D015394:Molecular Structure; D009570:Nitriles / Q000737:chemistry*; D010069:Oxadiazoles / Q000138:chemical synthesis / Q000737:chemistry; D010087:Oxides / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D009570:Nitriles; D010069:Oxadiazoles; D010087:Oxides