title: Regioselective haloaromatization of 1,2-bis(ethynyl)benzene via halogen acids and PtCl2. Platinum-catalyzed 6-pi electrocyclization of 1,2-bis(1'-haloethenyl)benzene intermediates.
abstract: [reaction: see text] Treatment of 1,2-bis(ethynyl)benzene (1) with aqueous HX (X = Br, I) in hot 3-pentanone (100-105 degrees C, 2 h) afforded 1,2-bis(1'-haloethenyl)benzene species 2-Br and 2-I in 98% and 95% yields, respectively. The hydrochlorination of endiyne 1 failed to proceed at elevated temperature but was implemented efficiently by PtCl2 (5 mol %) in hot 3-pentanone (100 degrees C, 2 h) to give 1,2-bis(1'-chloroethenyl)benzene 2-Cl in 80% yield. In the presence of PtCl2 (5 mol %), these halides 2-Cl,2-Br, and 2-I were subsequently converted to 1-halonaphthalenes 3-Cl, 3-Br, and 3-I in the mother solution via sequential 6-pi electrocyclization and dehalogenation reactions. PtCl2 (5 mol %) also effected direct haloaromatization of endiyne 1 with HX (X = Cl, Br, I) and gave 1-halonaphthalenes 3-Cl, 3-Br, and 3-I in 64-71% yields. This investigation reports the scope and the regioselectivity of haloaromatization of various enediynes catalyzed by PtCl2.
authors.affiliation: Department of Chemistry, National Tsing-Hua University, Hsinchu, Taiwan 30043, ROC.
authors.forename: Ching-Yu
authors.initials: CY
authors.lastname: Lo
authors.forename: Manyam Praveen
authors.initials: MP
authors.lastname: Kumar
authors.forename: Hsu-Kai
authors.initials: HK
authors.lastname: Chang
authors.forename: Shie-Fu
authors.initials: SF
authors.lastname: Lush
authors.forename: Rai-Shung
authors.initials: RS
authors.lastname: Liu
mesh_terms: D001555:Benzene Derivatives / Q000737:chemistry; D002384:Catalysis; D003500:Cyclization; D006846:Hydrocarbons, Halogenated / Q000138:chemical synthesis*; D010984:Platinum; D011084:Polycyclic Aromatic Hydrocarbons / Q000138:chemical synthesis*
chemical_list: D001555:Benzene Derivatives; D006846:Hydrocarbons, Halogenated; D011084:Polycyclic Aromatic Hydrocarbons; D010984:Platinum