title: Palladium(0)-catalyzed intramolecular [2+2+2] alkyne cyclotrimerizations with electron-deficient diynes and triynes.
abstract: In the presence of 2.5 mol % of [Pd(2)(dba)(3)] (dba=dibenzylideneacetone) and 5 mol % of PPh(3), nearly equimolar amounts of dimethyl nona-2,7-diyne-1,9-dioate derivatives (diyne diesters) and dialkyl acetylenedicarboxylates were allowed to react in toluene at 110 degrees C to afford [2+2+2] cycloadducts in moderate-to-good yields. Similarly, dimethyl trideca-2,7,12-triyne-1,13-dioate derivatives (triyne diesters) were catalytically transformed into phthalic acid ester analogues in excellent yields. To gain insight into the mechanism of these intramolecular alkyne cyclotrimerizations, stoichiometric reactions of [Pd(2)(dba)(3)] with a diyne diester and a triyne diester bearing ether tethers were conducted in acetone at room temperature to furnish an oligomeric bicyclopalladacyclopentadiene and a Pd(0) triyne complex, respectively. The structures of these novel complexes were unequivocally determined by Xray structure analysis. The isolated triyne complex was heated at 50 degrees C or treated with PPh(3) in acetone at room temperature to afford the arene product. Furthermore, the same complex catalyzed the triyne cyclization with or without PPh(3).
authors.affiliation: Department of Molecular Design and Engineering, Graduate School of Engineering, Nagoya University, Chikusa, Nagoya 464-8603, Japan. yamamoto@apchem.nagoya-u.ac.jp
authors.forename: Yoshihiko
authors.initials: Y
authors.lastname: Yamamoto
authors.forename: Asako
authors.initials: A
authors.lastname: Nagata
authors.forename: Hitomi
authors.initials: H
authors.lastname: Nagata
authors.forename: Yoji
authors.initials: Y
authors.lastname: Ando
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Arikawa
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Tatsumi
authors.forename: Kenji
authors.initials: K
authors.lastname: Itoh